Discus Culture...七彩魚飼育...
Water
Water is as important to the discus as air to us. It is the media in which it lives, grows, reproduces and dies. Water affects discus by both its physical and chemical properties. It is the most important environmental factor to account for success in both the culture and breeding of discus.
Physical Property
Water Temperature
Wild discus prefers to live in floodplains (igapós in Portuguese) and flooded forest which are always connected to a large body of water. These lentic habitats have soft and acidic water which are almost free of suspended materials. Some populations are found in alkaline water but this is the exception. The Amazon River basin is very close to the equator where the climate is hot and humid year round. Its mean water temperature from Belém to Manaus is 29-30°C.
Optimum Temperature Range for Discus
Discus is a poikilothermic organism. This means it cannot regulate its body temperature. Metabolism of the fish speeds up and slows down together with the changes in water temperature.
In the aquarium, discus can survive within the temperature range of 20-38°C. It can live for a few hours in 38°C water, provided there is good aeration in the tank. The discus' body systems begin to shut down at 15-16°C. Death occurs at around 13°C.
Discus is best maintained at 27-32°C. Adults are best kept below 30°C; 27-29°C is ideal. Youngsters grow faster at the higher temperature range of 30-32°C. As soon as they reach puberty, which is around the age of 16-18 months, they should be kept below 30°C. It is not necessary to maintain a very steady temperature in the aquarium. A healthy discus can take a sudden change of 4-5°C without any problem.
Breeding is another matter. A lower temperature is favourable. The optimum range is 26-28°C. Temperature changes of a few °C help to induce spawning. In the late afternoon, a 20% water change with cooler water (3-4°C) is helpful. The addition of new and cool water mimics rain in nature.
Discus stops spawning and the hatching rate of the fertilized eggs decreases rapidly when subjected to a water temperature of over 30°C for more than a week. The use of a water chiller in places that have a hot summer is a must to ensure breeding success.
Dissolved Gases: Oxygen
Discus obtains its oxygen from water through its gills. While land animals have 20% oxygen to breath from the atmosphere, there is only a few parts per million (ppm) of dissolved oxygen in water. The amount of oxygen that can dissolve in water is dependent on several factors. The value is inversely proportional to the amount of dissolved substances in water and its temperature. The amount of dissolved oxygen is increased by an increase in water pressure.
Aeration
In the aquarium, gaseous exchange at the water/air interface is insufficient to supply enough oxygen to discus in any tank having a realistic stocking density. When the dissolved oxygen value drops to 2 ppm, signs of hypoxia appear, specifically rapid breathing, flared opericula, head turned upwards gasping for air at the water surface. Discus dies in water with a dissolved oxygen value of 1.5 ppm.
Aeration is necessary to increase the surface area where gaseous exchange can take place. An air stone producing small bubbles aeriates better than the one with large bubbles since small bubbles have more surface area. Another function aeration serves is to drive away dissolved carbon dioxide (CO2), a toxic metabolic waste produced by discus.
Other Dissolved Gases
Besides oxygen, water also contains other dissolved gases. Rain water and surface water contain a lot less dissolved gases in comparison to ground water. Ground water should be aerated for a day to expel dissolved gases and then passed through active carbon to make it suitable for discus culture.
Buoyancy of water
Water is a lot more buoyant than air, hence, aquatic organisms do not need a strong skeleton to support their body weight. They have evolved into many bizarre body forms as well as grow to enormous sizes. The price to pay for life in water is its viscosity. It takes a lot more effort for aquatic life forms to move around and that means a streamlined body is essential to minimize friction. Therefore, a high fin, high body discus incapablre of swimming fast to avoid predators is unfavorable for survival in nature.
Chemical Properties of Water
Total Dissolved Solids and Water Hardness
Conductivity
Water is a universal solvent. Almost anything can dissolve in it to a certain degree. A sample of 100% pure water does not conduct electricity. Its conductivity increases with the amount of substances the water contains. Conductivity is measured by the conductivity meter. The readings are in microsiemens per square centimeter, abbreviated as μS cm-1 or μS/cm.
Total Dissolved Solids
Total dissolved solids (TDS) is the term used to describe the inorganic salts and small amounts of organic matter present in solution in water. The principal constituents are usually calcium (Ca), magnesium (Mg), sodium (Na), potassium (K) cations and carbonate [CO3(2-)], bicarbonate [HCO3(-)], chloride (Cl-), sulfate [SO4(2-)], nitrate [NO3(-)] anions. The unit of TDS is milligram/liter (mg/L).
Water Hardness
General hardness (GH) measures the amount of magnesium and calcium ions dissolved in water. Carbonate hardness (KH) represents the amount of carbonates and bicarbonates. Water hardness is often not expressed as a molar concentration, but rather in various units, such as degrees of general hardness (dGH), German degrees (°dH), parts per million (ppm, mg/L, or American degrees), etc.
Osmosis and Active Absorption
Dissolved substances increase osmotic pressure of water which has profound effects on all aquatic life forms. The most important effect is water balance. Since there is no danger of dehydration in the aquatic environment, a water tight skin is not necessary. This means water can enter into or pass out of the body of an aquatic organism. The direction of water flow is governed by the difference in osmotic pressure. Law of physics states when two solutions of different strengths are separated by a semipermeable membrane, the thinner solution goes into the thicker one until an equilibrium of osmotic pressure is achieved. The body fluid of discus has a higher osmotic pressure than the environment to result in water entering its body continuously. The excess water is excreted by the kidney to maintain an osmotic balance. A discus dies from dehydration when put into a marine tank because water is constantly being extracted from its body at a rate that exceeds its osmoregulation capability.
The semipermeable nature of discus skin also allows substances to pass out or go into the fish. Gaseous exchange takes place at the gills through the thin walled blood vessels where oxygen diffuses into while carbon dioxide and ammonia leave the blood simultaneously. Discus, like other freshwater fishes, tends to lose salts to the water. These are replaced by active absorption at its gills and the skin inside the buccal cavity.
Optimum Conductivity Range for Discus
In its natural habitat of the Amazon River basin, the water source is either rain or surface runoff. Discus inhabits all three kinds of black-, white- and clear water rivers. Both the black and clear water habits have water with a conductivity of 10-20 μS cm-1 while those in white water rivers are higher at 40-140 μS cm-1.
In captivity, discus can survive in a very wide range of conductivity ranging from distilled water (5-15 μS cm-1) to about 20% sea water (8,000-10,000 μS cm-1) for a day or two. The optimum range for growth and keeping is 50-180 μS cm-1. There is no real problem up to about 300 μS cm-1. Discus begins to suffer above that value. Keeping discus in water with a conductivity below 50 μS cm-1 is perfectly fine for the fish, however, the lack of buffers in the soft water often kills the discus when the pH value falls to below 4.0. A conductivity of 60-100 μS cm-1 is best for breeding.
Demineralization and Purification of Water
Reverse Osmosis
There are several methods to remove dissolved substances in water. The first one is by reverse osmosis. In the reverse osmosis machine, water is forced through a membrane that only allows water molecules to pass through. The effluent is pure water in theory. In practice, some leakages at the membrane always occur. Conductivity of RO (reverse osmosis) water is 10-20 μS cm-1.
Ion Exchanger
By passing water through anion ion and cation ion exchange resins, all the charged molecules can be removed. Substances which are not charged remain in solution but some non charged molecules are also removed by adsorption on the surface of the resins. Conductivity of the deionized water has a higher range of variation as a result.
Distillation
Distillation makes use of the phenomenon when an aqueous solution is heated to 100°C at sea level, water becomes steam and rises to leave the solution. Steam when cooled down is pure water. Distilled water of average quality has a conductivity of 5-15 μS cm-1.
RO, distilled and deionized water contain too little minerals for both the culture and breeding of discus. It has to be mixed with tap or natural water containg a sufficient amount of minerals to obtain the desired conductivity value. It is safer to pass tap and natural water first through active carbon to remove contaminants before use.
Chemical Filtration: Active Carbon
Active carbon can be used to remove a lot of substances dissolved in water, such as pesticides, heavy metals and medications. Active carbon is most useful to remove chlorine (Cl) and chloramine (NH2Cl) in tap water or drugs in aquarium water. Very active, active carbon can even remove a certain amount of heavy metal. Active carbon works by adsorption which is the phenomenon molecules in the gaseous, liquid and solid state tend to adhere to a surface. Active carbon is carbon possessing a very large surface area for adsorption to take place.
Most active carbon contains ash. New carbon has to be washed with phosphoric acid before use. The best active carbon for discus is coconut shell carbon which is best suited to remove minute quantities of dissolved substances in water.
Active carbon dumps most adsorbed substances back into solution upon saturation. Changing the carbon as frequently as possible is the only way to prevent this from happening. For this reason, it is not recommended to use active carbon in the filter continuously. Active carbon should be used for a few hours in the aquarium to remove drugs. The carbon is then removed and discarded. For treatment of new water, pass it through active carbon very slowly only once.
pH
Definition
pH is - log 10 of the hydrogen ion concentration in moles per liter. It represents the acidity and alkalinity of a solution on which 7 is neutral, lower values are acid and high values are alkaline.
Mineral salts and many other substances separate into its anion and cation components when in solution. The electric charges carried by these ions change the pH of the solution.
Buffer
There are groups of compounds in water working together to maintain pH. These are called buffer systems. The most important buffer system in the aquarium is the carbon dioxide, carbonate and bicarbonate system. Carbon dioxide produced by aquatic organisms becomes carbonic acid in water to produce a pH drop. The system works by neutralizing the carbonic acid with bicarbonate ions in water.
pH is very important in the physiology of discus. A few of the most important examples are:
1) The first effect of pH is on the hydrolysis of ammonia, a toxic bi-product of metabolism. Dissolved ammonia (NH3) is converted into the harmless ammonium ion (NH₄⁺).
2) The majority of fish enzymes, including those of discus, have an optimum pH to work. These enzymes act as catalysts in the synthesis of all kinds of body substances such as hormones, fats, proteins and other body tissues. They also facilitate catabolism reactions such as the breaking down of food to generate energy.
3) pH also affects availability of certain nutrients. Metals, such as iron, gradually go out of solution as the pH rises to become unavailable to aquatic organisms.
Optimum pH Range for Discus
Wild discus are found mainly in acid water habitats with a pH value as low as 4.2. In the aquarium, discus can survive within the pH range of 3.6-8. Optimum range for keeping is 5-6.5. Optimum pH range for breeding is 4.5-6. All my best strains were bred in water with a pH value 5.5-6. A low pH has an inhibitory effect on the growth of microorganisms. The mucus of discus is also thicker in an acidic environment.
Discus can live in alkaline water but it is suffering all the time, especially from ammonia poisoning. It is more prone to diseases. Please remember, the fact that wild discus is found in alkaline water does not mean it is living in an optimum environment. All my experience indicated discus grows and breeds better in acidic water.
A sudden change in pH is to be avoided at all times. It produces severe damage to the skin, eyes and gills of the discus. Discus adjusts better to a sudden lowering of pH rather than the reverse.
Adjustment of pH
The easiest method is to use phosphoric acid. This can be carefully added directly into the tank 1 milliliter (ml) at a time with a plastic syringe. It is safer to dilute the acid with five times water to avoid an accidental overdose. For our purpose, the food grade is pure enough.
Sources of Pollution in Aquarium
There are two major sources of pollution in the discus aquarium. The first is metabolic wastes of the fish which are carbon dioxide, ammonia and urea. The second are solid wastes.
Carbon dioxide and ammonia are released into the water by diffusion at the gills. Urea passes out of the discus body through the anus. Urea is hydrolyzed into ammonia and carbon dioxide by microbes.
Ammonia is converted into nitrate in a two steps aerobic process known as nitrification by two genera of gram-negative chemoautotrophic bacteria as follows:
1) Nitrosomonas bacteria oxidize ammonia into nitrite in a process known as nitritation.
2) Nitrobacter bacteria convert nitrite into nitrate.
N.B.
Nitrification is performed by fungi in most discus habitats in the Amazon River basin because bacteria do not grow well in acidic water. The optimum pH for Nitrosomonas bacteria is 6.0-9.0 and 7.5-8.5 for Nitrobacter bacteria.
Biological Filter
A working biological filter is essential to maintain water quality in the discus aquarium. Its three major components are: the filter medium, the container and the power source.
Filter Medium
Nitrosomonas bacteria are photophobic organisms. They generate a biofilm matrix or form clumps with other microbes to avoid light. Nitrobacter bacteria are sedentary organisms. A good filter medium must have a large surface area versus volume for the bacteria to attach and grow. While pebbles, coarse sands, chopped plastic pipes or ceramic rings will work, the bio ball performs much better. It is designed to have a lot of internal surfaces for the bacteria to attach and its spherical shape also facilitates air circulation.
Filter Container
The other important design parameter for a biological filter is an amply oxygen supply. In this respect, the totally enclosed Eheim type is a poor design: water has only a few parts per million (ppm) dissolved oxygen while air has 20% oxygen.
Power Source
A biological filter can be operated by air or a pump. Air operated filters are the sponge filter and under gravel filter. They are cheap and economical to run but are not powerful enough to handle the wastes produced in a well populated aquarium of growing discus. The Japanese design consisting of a rectangular plastic box, a removable lid, a spray bar and a small pump sitting on top of the aquarium is most useful for discus.
Water Change
A second source of pollution is faeces and other solid wastes including uneaten foods, mucus of discus, its dead skin cells, unfertilized eggs and the occasional carcass of a dead discus. These are the food for a plethora of other organisms that also live in the aquarium. The end product of their metabolism are many compounds which are all released into the water.
While ammonia can be removed by the biological filter, carbon dioxide by aeration, but all the other pollutants can only be diluted by water change.
With regard to the amount of water change, change as much and as frequently as you can.
Discus Food
All animals need food. It serves the dual function to supply energy and also as the source of raw materials for growth, reproduction and tissue repair. Food has to be available not only in an adequate amount but it must also contain all the essential nutrients. A deficiency in one or more of these results in poor health conditions, diseases or death.
Like every other animal, discus needs carbohydrates, proteins and fats in its diet. It also requires a small amount of vitamins and trace elements to stay healthy. Extensive research on the nutritional need of fish has been done only on a few economically important food species such as the common carp (Cyprinus carpio) and salmon (Salmo salsa). No scientific study has ever been made on discus.
Carbohydrates
Carbohydrates are a group of organic compounds made up of carbon, hydrogen, and oxygen. The general empirical structure for carbohydrates is (CH2O)n. The building blocks of all carbohydrates are simple sugars called monosaccharides. The saccharides are divided into five chemical groups: monosaccharides, disaccharides, trisaccharides, oligosaccharides, and polysaccharides.
Carbohydrates perform numerous roles in living organisms.They are the most abundant and accessible dietary source of energy for various metabolic activities. Monosaccharides are the major fuel source for metabolism, being used both as an energy source and in biosynthesis. The most important monosaccharide is glucose which is metabolized by nearly all known organisms. The fuel value of the three categories of foodstuffs are as follows:
carbohydrates 4.l Kcal ( l Kcal= 1,000 cal)
Proteins* 5.6 Kcal (in animal the protein value is 4.1 because urea and some other products of protein metabolism are not "burned".)
Fats 9.0 Kcal
*Proteins are not burnt unless carbohydrates are not available.
Carbohydrates also serve as energy storage. Dietary carbohydrates are broken down in the intestine by digestion into simpler forms. When monosaccharides are not immediately needed by many cells, they are often converted to more space-efficient polysaccharide forms. In discus they are stored as glycogen in liver and muscle cells.
In addition, carbohydrates are intermediates in the synthesis of fats and proteins.
The 5-carbon monosaccharide ribose is the backbone of the genetic molecule ribonucleic acid (RNA) and the related deoxyribose is a component of deoxyribonucleic acid (DNA). Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system, fertilization, preventing pathogenesis, blood clotting, and development.
A good discus diet should contain at least 20% carbohydrates, mostly as glycogen.
Proteins
Proteins are the main constituent of the discus' body. The whole fish carcass contains on average 75% water, 16% protein, 6% lipid, and 3% ash. With the exception of water, proteins are among the most important constituents of all living cells and represent the largest chemical group in the animal body.
Proteins are made up of amino acids which contain amine (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. Besides the key elements carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), other elements are found in the side chains of certain amino acids. About 500 naturally occurring amino acids are known but only 20 of them, known as proteinogenic (protein creating) amino acids are encoded directly by triplet codons in the genetic code and are known as "standard" amino acids. Some proteins are made up to as many as a hundred amino acids.
Dietary protein may be catabolized as a source of energy. However, animals (including discus) will only burn its body protein for energy only in the absence of carbohydrates, specifically under starvation. Dietary protein is required within the animal body for the formation of hormones, enzymes and a wide variety of other biologically important substances such as antibodies and haemoglobin.
Proteins are essential components of both the cell nucleus and cell protoplasm. The bulk of the muscle tissues, internal organs, brain, nerves and skin are made of proteins. Proteins also serve as a substrate for the formation of tissue carbohydrates or fats. They are used to repair worn or wasted tissue and to build new tissues for growth.
An ample supply of proteins must be provided in the discus diet. Studies indicate fish need at least 30-36% protein in its diet in order to grow well. Discus needs at least 40% proteins in its diet to stay healthy.
Two factors have to be considered when selecting the protein source for discus. Firstly, there are ten essential amino acids (EAA) that fish cannot synthesis in its body or at a rate sufficient to meet its physiological needs, which are: threonine, valine, leucine, isoleucine, methionine, tryptophan, lysine, histidine, arginine, phenylalanine. The discus diet must contain a sufficient amount of all of them. Another factor is protein digestibility since not all proteins are equally digested and absorbed by discus.
Fats (Lipids)
Fats (lipids) are the third main macronutrient groups in discus diet. The main difference between fats and lipids is lipids are a broad group of biomolecules while fats are a type of lipid.
A fat is made of two kinds of smaller molecules: glycerol and fatty acids. Glycerol is a simple polyol compound with chemical formula C3H8O3. A fatty acid is a chain of carbon atoms, joined by single, double, or (more rarely) triple bonds, with all remaining free bonds filled by hydrogen atoms. An important classification of fats is according to how the carbon atoms are linked, which are: saturated, unsaturated and trans fats.
Saturated Fats
The fatty acid chains in the saturated fats have all or predominantly single bonds. Where double bonds are formed, hydrogen atoms are subtracted from the carbon chain. Saturated fats have the maximum number of hydrogens bonded to the carbons, and therefore are "saturated" with hydrogen atoms. Most animal fats are saturated.
Unsaturated Fats
Unsaturated fats are fats or fatty acids in which there are at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated (ω−7 ω−9) if it contains one double bond, and polyunsaturated (ω−3 ω−6) if it contains more than one double bond. The fats of plants and fish are generally unsaturated.
Trans fats
Trans fat is a fat molecule that contains one or more double bonds in trans geometric configuration which means the carbon chain extends from opposite sides of the double bond to result in a straight molecule. Trans fats occur in a small amount in animal fats.
Important Roles in Animals
1) Fats (lipids) are a major and dense source of food energy. Each gram of fat when burned or metabolized releases about 9.0 kcal. Free fatty acids derived from triglycerides (tri-esters consisting of a glycerol bound to three fatty acid molecules) are the major aerobic fuel source for energy metabolism of fish muscle. Under such a circumstance, dietary lipids can be used to spare the more valuable protein for growth. Excess dietary fats are stored in body tissues. Animals can also convert excess ingested carbohydrates to be stored in a more compact form as fats and oils. (The only difference between fats and oils is that the latter are liquid at room temperature, whereas fats are semi-solid at room temperature.) The actual rate of fatty acid synthesis de novo is inversely related to the level of lipid in the diet.
2) Other functions:
A) Fats (lipids) are essential components of all cellular and subcellular membranes.
B) Lipids serve as biological carriers for the absorption of the fat soluble vitamins A, D, E and K.
C) Fats are a source of essential steroids, which perform a wide range of important biological functions.
Warm freshwater fishes, including discus, have a requirement for polyunsaturated fatty acids. Saturated and trans fats have little value in fish nutrition. The diet for discus should contain at least 15% fats and the minimum amount of saturated and trans fats.
Vitamins
Vitamins are organic molecules that an organism needs in small quantities for the proper functioning of its metabolism. Certain vitamins exist in a chemically closely related set of molecules known as vitamers.
There are thirteen vitamins : vitamin A , vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), vitamin B7 (biotin), vitamin B9 (folic acid or folate), vitamin B12 (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones).
Vitamins have diverse biochemical functions. Vitamin A acts as a regulator of cell and tissue growth and differentiation. Astaxanthin is the precursor of pro Vitamin A which helps the discus to see better in the dark environment. It is also essential for the development of red color in discus. Astaxanthin is a substance that discus cannot synthesize and must be obtained from its diet. It is a blood-red keto-carotenoid pigment with a chemical formula C40H52O4. Astaxanthin is produced naturally by various freshwater microalgae and fungus.
Vitamin D provides a hormone-like function, regulating mineral metabolism for bones and other organs. The B complex vitamins function as coenzymes or the precursors for them. Vitamins C and E function as antioxidants.
Minerals
These can be divided into macro minerals and trace minerals according to the amount needed by the discus.
The macro minerals are: sodium, potassium, chloride, calcium, phosphorus, magnesium, sulfur.
Trace minerals (microminerals) are: iron, zinc, iodine, selenium, copper, manganese, fluoride, chromium, molybdenum.
Other trace nutrients known to be essential in tiny amounts include nickel, silicon, vanadium, and cobalt.
Diet of Wild Discus
Discus is a carnivorous, opportunistic feeder. The diet of discus in nature consists mainly of shrimps and bloodworms. It will eat other small organisms such as small fishes, crustaceans, insects, annelids, isopods, gastropods, etc., whenever there is the opportunity.
World Wide Fish Farm Discus Food Recipes
First Recipe
The first recipe was a mixture of minced half-and-half trimmed beef heart/marine shrimp meat, which was fortified with vitamins and minerals. (Beef heart was replaced in the later years by lean beef.) Shrimp meat, besides its nutritional value, also serves to bind the mixture together. I have substituted the Macrobrachium shrimp with marine shrimps (Penaeus and Parapenaeopsis spp.) to avoid the introduction of parasites. Parasites carried by marine organisms usually cannot infect fresh water fishes. I did not use fish meat for the same reason. Discus grows very fast on this food mixture but cannot breed well. Why is it so? Fish in general have difficulty in digesting saturated and trans fats which amounts to roughly 40% of the fats in beef.
Second Recipe
The final modification of the formula was to replace beef with scalded bloodworm (cook in boiling water for 1-2 minutes or until the color changes from red to grey). 2-3% of marine crab eggs was also added for an additional source of astaxanthin and nutrients. When crab eggs were unavailable, we added a small amount of synthetic astaxanthin which was first dissolved in hot water to the food mixture. This fortified half-and-half bloodworm/shrimp meat formula was the staple food in WWFF from 1986 to 2005.
Breeders were fed twice daily with bloodworm which is essential for successful breeding, especially for delicate inbred strains. The other meal was the regular food mixture. To make the bloodworm more safe to feed, we purchased the best quality live worms and washed them really well with tap water to remove all dead worms and debris. The washed worms were then stored in the deep freezer for three weeks at -18°C. This process should kill all the parasites but not their eggs.
NB.
Do not add the vitamins and astaxanthin to the food mixture if it is going into the deep freezer. Add them after the mixture has thawed, immediately before feeding.
Disease
ABOVE: Discus infected with "Discus AIDS"
Discus diseases can be classified into four main categories: environmental diseases, nutritional diseases, toxicity diseases and parasitic diseases.
Environment Diseases
Poor Water Conditions
Most environmental diseases are the result of poor water conditions.
Temperature
Discus is a poikilothermic organism which means its metabolism goes up and down according to the variation in water temperature. A low metabolism weakens the discus to make it more susceptible to diseases. External wounds are more likely to be infected by bacteria and fungi when a discus is subjected to low temperatures.
High temperatures were used to treat parasitic infection in discus for many years. German breeders subjected discus to 38°C water for 7-8 hours. All parasites were killed but the discus became sterile: its gonads were destroyed by the heat.
pH
Alkaline water is an extreme torture to discus. Discus in alkaline water is weaker and is in a constant danger of ammonia poisoning. If a discus is transferred suddenly from acidic water to alkaline water, severe damages occur at the gills, eyes and skin. Such burns are analogous to pouring concentrated hydrochloric acid or caustic soda solution onto our skin.
Pollutants
Toxic metabolic wastes such as carbon dioxide, ammonia and nitrite can debilitate or even kill discus at high concentration. An excess of uneaten food and a dirty filter can create hypoxia or even death when the putrefying processes take up too much oxygen in the water. Ectoprotozoan parasite infections are usually triggered by dirty aquarium water.
Confinement and Excess Light
Confinement is a strong stress to newly captured wild discus. All discus, domestic and wild alike, do not like strong light from the sides and direct sunlight. They also have a rapid escape response to shadow. In nature, a shadow means an approaching predator.
Photoperiodism
Photoperiod acts as the biological clock for the discus to synchronize its metabolism. There is approximately 13 hours of daylight year-round in the Amazon River basin. Adult discus can adapt to do well in 18 hours of light in captivity but it needs at least six hours of rest in darkness to stay healthy. Young discus (free swimming stage to two months old) tolerates continuous light. It grows faster by feeding non stop. The young discus gradually loses this ability over the next few months to behave like an adult at around six months of age.
Nutritional Diseases
Nutritional diseases occur when the discus is fed on imbalanced or deficient diets.
Fatty Acid Degeneration (FLD) or Hepatic Steatosis
FLD is a disease beginning with saturated fats (triglycerides) are deposited inside the cytoplasm of the liver cells. Small fat vacuoles occur around the nucleus at the beginning. In this stage, liver cells are filled with multiple fat droplets that do not displace the centrally located nucleus. In the late stages, the size of the vacuoles increases, pushing the nucleus to the periphery of the cell to result in its death. Massive liver cell loss and inflammation at the advanced stage of FLD lead to failure of liver function. Death is imminent.
The exact cause of FLD in discus is unknown. It occurs when discus is fed with too much fats, especially those that contain a lot of saturated fats, such as beef/beef heart, tubifex, white and grindal worms. The best discus diet should contain minimum saturated fats and not more than 15% fats.
Deficiency Diseases
A common dietary problem is amino acid deficiency. Beef heart/beef and the annelid foods (tubifex, white and grindal worms) are deficient in some essential amino acids for fish. Discus can grow very fast and big on such diets but it is less colorful as well as more prone to diseases. Male fertility is generally low too. For discus, adult artemia is also deficient in some amino acids while the nauplius is a complete, balanced food organism. Discus needs at least 40% proteins in its diet to stay healthy.
When there are insufficient carbohydrates in the diet, the discus is forced to burn its precious proteins for energy. It is not only wasteful but the catabolic process produces a lot more toxic by-products as well. Turkey heart, a common ingredient of discus food recipes in America and Europe, contains very little carbohydrates. It is a deficient food for discus. Discus needs at least 20% carbohydrates (mostly as glycogen) in its diet.
Vitamin deficiency is a common problem for discus fed on dry foods. Vitamins are fragile compounds that cannot withstand high heat or extreme cold. The high heat necessary in the manufacturing process had destroyed all the vitamins in dry foods. Frozen foods can also be vitamin deficient for the same reason.
Another common deficiency disease is insufficient food. The discus must be able to obtain sufficient quantities of all the essential nutrients every day for it to reach its full potential in growth and reproduction. Many breeders underfeed their discus on purpose with the presumption that large discus breed poorly. This is only true for fishes that have FLD.
In WWFF, we fed our growing discus six times a day on an amount that was consumed in 10 minutes. Pairs were fed three times a day. Immediately after each meal, the aquaria were siphoned clean, followed by a big water change.
Toxicity Diseases
Toxins in Water
The most common toxins are those found in water. With pollution getting worse rapidly worldwide, water without toxins is as precious as gold. Surface water often contains pesticides, industrial wastes and heavy metals. Ground water can contain hydrogen sulphide as well as excessive amounts of carbon dioxide and nitrogen gas.
Most city water contains chlorine as the sterilization agent. Chlorine reacts with organic compounds (naturally occurring or as a result of pollution) in water to produce trihalomethanes (THMs), which are suspected carcinogenic agents. In many countries, chloramine (NH2Cl) is used instead which is produced by injecting chlorine together with ammonia into the water simultaneously. To prevent the formation of THMs, an excess of ammonia is utilized resulting in many cases up to 1 ppm of residual ammonia in the tap water. Ammonia, chlorine and chloramine are extremely toxic to discus. While chlorine can be driven out from solution by aeration or neutralized with sodium thiosulphate (Na2S2O3), chloramine is a stable compound which can remain in water for weeks. It can only be removed by active carbon. Ammonia is removed by the biological filter. Heavy metals can be chelated with 0.5-1 ppm (0.5-1 mg/L) EDTA (ethylenediaminetetraacetic acid, C10H16N2O8).
Drug Toxicity
All discus medications were orginally developed to treat human or livestock parasites belonging to different species or even different genera as those found in discus. High concentrations of these antihelminthics had to be used to control discus parasites. Vital organs such as the liver, spleen and kidney are damaged due to drug toxicity. Most of the sudden deaths of discus in the aquarium is the result of organ failure. Damaged gonads result in a reduction in fertility or even sterility if they are destroyed. Use all drugs with extreme caution and never use them together. Always allow a rest period of 5-7 days between treatments.
Head Standing
Discus sometimes becomes head standing. The condition is produced by an inflammation of the duct that connects the swim bladder to the intestine. The blockage of the duct makes the discus unable to regulate the amount of gas in the swim bladder. The cause for the inflammation in discus is most probably a result of drug toxicity and genetics. Some strains became head standing after receiving the all-in-one flubendazole, metronidazole and acetone treatment but no heading standing occurred in other similarly medicated strain. There is no cure for head standing
Food Poisoning
An excess amount of vitamins and astaxanthin in the food is toxic to discus. Dry foods contain preservatives, artificial favors and coloring agents that are harmful to the discus.
Food poisoning can occur when the discus is fed with contaminated food. Food organisms living in rivers and shallow seas near cities are consuming foods that are loaded with industrial wastes and pesticides. When fed to discus, these toxins are accumulated in the body tissues and eventually will affect its health. Till now we know almost nothing about the amount of each toxin the discus can tolerate.
Sex Hormones
The sex hormones, androgen (testosterone), oestrogen and progesterone has been used for decades to enhance colors in discus. The damage to the gonads is dependent on the dosage and the age of the discus when the hormone treatment is administered. A massive dose given to 6-10 weeks discus will lead to sterility. An adult discus can tolerate several mild doses without any ill effects. Many breeders, including Dr. Schmidt-Focke, believe the development of a streamer on the dorsal fin is produced by sex hormones in its beef heart food, nonetheless, there are wild discus having such an extension and hybrid discus raised without beef heat possessig a streamer on both the dorsal and anal fins.
Dropsy/Bloat
Feeding tubifex can result in a condition known as bloat or dropsy which is incurable. The discus suffering from this disease has a swollen abdomen together with raised scales and eventually becomes head standing. Bloat is thought to be caused by the bacteria and virus as well as toxins inside the tubifex food.
Parasitic Diseases
Parasitic disease is the number one problem in discus culture. There are two reasons. Firstly, brooding discus feed their larvae with their skin cells. While this is a brilliant survival tactic in nature, the close relationship between parents and offspring facilitates transmission of hexamita, capillaria and gill flukes. These are very debilitating discus parasites which are capable of direct fish to fish transmission without the need of an intermediate host.
Secondly, even though almost all wild discus have parasites, they can harbour them without much of a problem in the Rio Amazonas. The parasite/host relationship begins to shift in favor of the parasites only after the discus has been captured and is weakened by hunger and stress during the long journey to the exporter's facility. A bigger problem occurs when the debilitated discus arrives at the importers' aquarium which is loaded with different strains or even other species of capillaria, hexamita, gill worms and other pathogens. All these critters are brought in together with fishes from many parts of the world. The wild discus succumbs to the combined attacks of the old and new parasites. The new pathogens are a lot more damaging because the discus has no immunity against them. The same is equally true for tank raised varieties that had spent some time in a wholesaler's facility.
Although the solution to parasite infections is artificial raising, very few breeders are able to master this decades old technique well enough to have good results. Nearly all the world's discus are bred naturally and are all sick.
Parasites are brought into the hatchery together with new discus if they are quarantined for only a few days and the breeder replies merely on external symptoms to judge their health condition. Such a practice is not reliable. A healthy looking discus can harbour parasites. However, the proper quarantine procedures are lengthy and demanding. While the detection of gill fluke and capillaria is easy, it is very difficult for hexamita which can only be seen under the microscope at high magnification and that requires considerable training to become proficient. The new discus had to be treated if they have parasites. This prolongs the quarantine period from three weeks to 2-3 months.
The control of hexamita, capillaria and gill flukes is very difficult in a discus hatchery. Hexamita has been the main problem due to its resistance to metronidazole, the most widely used drug to control the parasite. A complete cure is rarely achieved and relapses are the rule. The treatment of gill worms and capillaria is complicated by their eggs which are found everywhere in the aquarium. The anthelmintics only kill the adult but the egg can survive from the protection of its shell. This means multiple treatments are necessary to control these parasites.
Hexamita (Hexamita spp.)/Spironucleus (Spironucleus spp.)
The correct name of hexamita is spironucleus. It is a flagellate having a spindle shaped body and eight flagellates, two anterior and six posterior. It has two nuclei, each one is associated with four flagellates. Hexmita moves around in a jerky, spiral manner performed by beating it flagella. It is only visible under the microscope at high magnification (600-800X) as a very motile organism. The flagellates are only visible at much higher magnification (1,500X and above).
Hexamita is found in a small number in the intestine of nearly all captive bred discus. This small population is well tolerated by the host. When the discus becomes weak, the parasite multiples very quickly and begins to migrate from the intestinal tract into the internal organs and tissues. Renal tubules and gill capillaries are blocked by crystalline deposits. Severe damages to these vital organs occur at this advanced stage of infection.
Hexamita multiplies asexually by binary fission under favourable conditions. Sexual reproduction has never been observed. Under adverse conditions, some of them shed the flagellates and develop a thicker cell wall. This encapsulated form is thought to enable the organism to survive dryness for a short period of time. Hexamita can survive outside of the host in the aquarium water for 2-3 days.
Hexamitasis, the disease produced by hexamita infection, has no distinctive symptoms. Conditions such as emaciation, black eyes and loss of appetite are symptoms common to both hexamitasis and capillaria infection.
Hexamitasis is often confused with hole-in-the-head (HITH) disease. The latter is often thought to be a form of hexamitasis, but the parasite has never been found inside the holes or in the pus extruded from these crevices. The condition is most probably a form of lateral line erosion, a deficiency disease.
Treatment
Metronidazole is the drugh of choice to treat hexamitasis till today. Unfortunately, its effectiveness has gradually decreased year by year since the late 1970s. In order to be effective, the drug has to be administered at a high dosage of 7 ppm (7 mg/liter) together with high water temperatures of 33-35°C. This treatment becomes very damaging to the gonads. Many discus have a reduction in fertility or become sterile after several doses.
It was only in the mid 1990s when a young German scientist discovered metronidazole is metabolized within a few hours by microbes inside the aquarium's biological filter. Hence, the latest and most effective treatment for hexamita is a bath of metronidazole* at a concentration of 4 ppm (4 mg/L) in the aquarium water for three days at the normal water temperature of 28-30°C with the biological filter switched off.
* metronidazole: 1-(b-Hydroxyethyl 1)-2-methyl-5-nitroimidazole
Capillaria pterophyllum (thread worm)
C. pterophyllum is a nematode found in the intestine of the discus. It is several centimeters long, translucent, very thin, tapers at both ends and thus gives rise to the common name of thread worm. The parasite feeds on tissues of the intestine. The female worm, after copulation with a male, lays many eggs which pass out to the aquarium water together with the host's feces. The egg of Capillaria is visible under the microscope at 100X. It is translucent, oval in shape and the cell wall is thickened at both ends, which is a distinguishing feature of thread worms. Depending on water temperature, the egg develops into a larva in 10-20 days which is viable for months in the aquarium. At this stage, the larva containing egg becomes infective if ingested by the discus.
Capillaria is a very debilitating parasite due to the heavy damages inflicted to the intestinal wall when it feeds. Discus with a mild capillaria infection has a slightly distended abdomen and faces the back wall of the aquarium all the time. The long, stringy feces consists of alternate dark and light colored segments which is attached to the anus of the infected discus for a long time. As infection advances, the fish stops eating and becomes emaciated. It is not unusual for a discus to be heavily infected with both hexamita and capillaria.
Treatment
Flubendazole: methyl N-[6-(4-fluorobenzoyl)-1H-benzimidazol-2-yl]carbamate
The treatment for capillaria is 1/2 teaspoon of the 5% Flubenol powder per 100 liters of water for three days. The drug is best repeated three more times at a week's interval. The discus has to be transferred to a sterilized aquarium after each treatment.
Dactylogyrus spp. (gill flukes)
Gill flukes are minute monogenetic trematodes (flatworms). At a maximum length of 2-3 mm, they are visible to the naked eye. Monogeneric trematodes live on the gills of the discus but they are also found inside the buccal cavity and on the skin of heavily infected fish. They have four anterior eyes-spots and a mouth that is armed with teeth. The posterior end of the worm is equipped with suckers that have hooks for anchorage.
The hermaphroditic adult is oviparous and releases eggs into the water at the rate of 4-10 eggs per day. The egg hatch in 2-3 days and develops into a free swimming ciliated larva (oncomiracidium). Reinfection is frequent in the crowded aquarium when the oncomiracidium comes into contact with a discus.
Heavily infected discus breathes rapidly and even rises to the water surface with its mouth pointing upwards gasping for air. This is the result of the damages done by the worms feeding on the gills. Heavily infected discus invariably die of hypoxia.
Gill worms are a major problem for discus larvae, especially so when they are still feeding on the parent's body. The infected larva has flared gills, breaths very rapidly and scraps its body against objects in the aquarium. Death comes within a few days.
Treatments
1) The first method is to use Flubenol in the same way as for treating capillaria. However, the drug became ineffective after the mid 1990s.
2) The second treatment is a formalin** bath. Use 14-16 milliliters (ml) of 37% formalin per 100 liters of water (180-200 ppm) for one hour, followed by a 100% water change and salt for 1-2 days. Up to 300 grams of common rock salt can be added per 100 liters of water. Do not use formalin on discus with external wounds. The treatment can be repeated once after 3-4 days.
3) The best cure for gill worm is praziquantel*** applied in a bath of 0.5 ppm (0.5 mg/liter)concentration in the aquarium water for three days. The treatment is repeated at least once after a week. The drug can be dissolved in 5 milliliters (ml) propylene glycol (propane-1,2-diol) but this is not a must.
** formalin: a water-based saturated solution of formaldehyde gas (CH2O), which contains about 40% formaldehyde gas by volume or 37% formaldehyde gas by weight, as well as a small amount of stabilizer.
*** praziquantel: 2-(cyclohexylcarbonyl)-1,2,3,6,7,11b-texahydro-1H-pyrazino[2-1a]isoquinolin-4-one
Ectoprotozoan Parasites Infection (Trichodina spp., Cryptobia spp., Chilodonella spp.)
Discus is occasionally attacked by ectoprotozoan parasites, especially in spring. They are brought into the aquarium together with live freshwater foods. Nonetheless, a small number of them are always present in the tank. They can multiply very quickly under favourable conditions, specifically water containing high amounts of organic materials.
The symptom of the disease is either white or yellowish spots or a cloudy slime on the skin and fins. The discus twitches its fins and scrapes its body against objects in the aquarium. An infected discus often turns black and its fins are all closed when the infection is heavy.
1) The same treatment with formalin as for gill fluke is effective.
2) A bath in acriflavine**** with salt ( 200 grams/100 liters of water) for three days.
Malachite green is not recommended due to its high toxicity.
****acriflavine: 3,6-Diamino-10-methylacridinium chloride mixt. with 3,6-acridinediamine
Cestodes (tapeworms), Digenetic Trematodes (liver flukes) and Acanthocephalans (spiny- headed worms)
Other less common discus aprasites are cestodes, digenetic trematodes and acanthocephalans. These parasites have complex life cycles involving one to several intermediate hosts to make them incapable of spreading in the aquarium. They can all be treated with praziquantel in the food at the concentration of 1.5 mg/kg food.
Cestodes (tapeworms)
Cestodes are long ribbon-like parasites commonly found inside the intestine of the host. They have a head (scolex) that is permanently attached to the intestinal wall of the discus. Connected to the scolex is the neck, which is a region for growth. Posterior to the neck is a long chain of segments called proglottids. Cestodes are hermaphrodites. Each proglottid includes both male and female gonads and generates both sperm and eggs. Tapeworms can reproduce sexually, either through self-fertilization or cross-fertilization with another tapeworm. Some species can reproduce asexually by breaking off a section of proglottids which then regenerates into a complete worm. Cestod absorb nutrients, perform gaseous exchange and excretion through their tegument.
The species infecting discus is white, 5-10 mm wide, 8-12 cm long. Up to 10 worms have been found in a discus. The most heavily infected variety is Red Royal Blue. The infection should come from the wild moina food.
Tubifex is the intermediate host of some tapeworm species.
Discus tolerates tapeworms well. They are far less devastating parasites than capillaria, hexamita and gill flukes.
Digenetic Trematodes (liver flukes)
These are parasitic flatworms or flukes having a syncytial tegument. Most species have two suckers, one ventral and one oral. They are found in every organ and tissue of the host, including the eyes and brain.
Digenetic trematodes are rarely a problem for discus unless they are fed on large quantities of wild moina or other freshwater crustacean food infected with the intermediate stages of these parasites.
Acanthocephalans (spiny-headed worms)
Acanthocephalans live within the small intestines. They have a retractable proboscis armed with spines that is inserted into the mucosa as a holdfast. They have separate sexes and lack a digestive system. Acanthocephalans obtain nutrients, exchange gases and excrete wastes through its body wall.
Bacteria Infection
Discus rarely have bacteria problems. When it does occur, the infection is in the form of reddening and fraying of the fins and gills, body ulcer, swollen abdomen and also expophthalmos. The antibiotics treatments are as follows:
1) Vibramycin hydrochloride—15 ppm for seven days.
2) Erythromycin—15 ppm for seven days.
For the best result, a daily water change of 25% coupled with a 25% replenishment of the antibiotics. Systemic bacteria infections are usually incurable.
Saprolegnia Infection (water fungus)
Discus is rarely infected by fungus except when it is weak and has external wounds. The infection takes the form of a turf of cotton wool like structure that is attached to the fins and the wounded skin. The mycelium (plant body) of saprolegnia is visible under the microscope at low magnification (60X-100X).
Treatments
1) High water temperature of 32-33°C together with salt (up to 300 grams of rock salt per 100 liters of water) for a few days.
2) 5% solution of acriflavine or mercurochrome applied directly to the infection once per day until cured.
***** mercurochrome: (2,7-Dibromo-9-(2-carboxyphenyl)-6-oxoanthen-4-yl]mercury)
Virus Infection
Discus Plague or Discus AIDS
A new discus disease appeared in 1986. It was the dreadful Discus AIDS or Discus Plague orginated from the angel fish farm in Singapore and soon spreaded to infect discus outside of the country.
The disease begins with a white mucus film on the whole body looking very similar to an ectoprotozoan parasites infection. The discus twitchs its fins and scraps its body against objects in the aquarium. Within a few hours, all the discus in the tank turn black and clumps together. Some fish even lie flat on the tank floor.
There is no treatment. What we could do is to keep the tank as clean as possible by performing large daily water changes. A formalin bath is often helpful. The fish begin to recover after 5-6 days. Survival rate is over 90% for adults yet the mortality rate for youngsters (below 7 cm) is 100%. Infected discus could transmit the disease for as long as 10-12 weeks after recovery.
The Discus Plague was a big problem for more than five years after its first appearance in 1986. The disease gradually disappeared after all discus had developed immunity.
No pathogen has been identified to be responsible for the Discus Plague which is most probably a virus disease.
Quarantine
Prevention is the best cure for diseases. All newly acquired discus should be quarantined in a sterilized and isolated aquarium for at least three weeks. During this period of time, the discus should be examined frequently with a microscope. Skin and gill smear will reveal the presence of gill flukes. The eggs of intestinal parasites are found in the faeces. It is really worthwhile for a serious discus enthusiast to buy a microscope. A second hand one having a magnification of 600X is sufficient. Most discus parasites, with the exception of hexamita and bacteria, are visible below 200X. Diagnosis for hexamitasis is best done by sending a faeces sample to a veterinary laboratory. This is also true for suspected bacteria infections.
Always clean your hands thoroughly with water and detergent and then rubbing alcohol (isopropyl alcohol) before handling healthy discus.
Sterilization of Aquarium System
The cheapest way is by Clorox®. Before applying the bleach, remove the nylon wool in the biological filter and any other objects that cannot withstand bleach, such as sponge filter and heater. Wipe carefully all surfaces with Clorox® that get wet when the system is running, such as the top of the aquarium, surfaces of the filter box, air hose, etc. Use 200-300 milliliters (ml) of Clorox® per 100 liters of water for at least eight hours. If the dirt and algae on the glass are still brown, add more bleach and wait a few more hours. When everything has turned white, the water is drained completely and refilled. A tablespoon of sodium thiosulphate per 100 liters of water should be sufficient to neutralize the residual bleach. If in doubt, use more. The water is drained completely after the system has been running for 10-15 minutes and then refilled to complete the sterilization process. To sterilize the nylon wool and sponge filter, they should be cleaned first and then boiled in boiling water for 10 minutes. The heater is cleaned thoroughly with water and detergent and then soaked in rubbing alcohol for 2-3 minutes.
Automated Aquarium System
ABOVE: Diagram 1. Automatic Aquarium System
The backbone of a modern discus hatchery is the automatic aquarium systems.
Diagram 1 is a typical system installed in my hatchery in Taichung, representing the last stage in the evolution of my design. The large central vat has a 25% holding capacity of the whole system. Inside it are the biological filters and the oxygen reactor.
The aquarium tanks are placed on iron stands with its bottom 40 cm higher than the central vat.
Water is circulated to the tanks by a small pump (A) through a manifold. A plastic ball valve is installed to regulate the water flow, which is adjusted to a turn-over rate of a 100% of the system's total capacity in 20-30 minutes. A separate pump (B) sends water from the vat to the oxygen reactor.
The intake of the pumps is located in the optimum positions in the vat so as to ensure clean filtered water is sent back to the aquarium and dirty water from the aquarium is delivered to the oxygen reactor. The oxygen reactor also works as the second biological filter.
There are two stand pipes in the central vat. The larger one controls the water level of the vat which can be removed for draining the vat completely. The shorter stand pipe is a part of the automatic water changing system. It is connected to a solenoid valve. A timer is set to open the value at specific time intervals in the day to drain water from the vat. Water coming from the fresh water supply pipe fill up the vat after the solenoid valve is closed.
The system is heated by hot water from a boiler passing through the stainless steel coils. A thermostat regulates the water temperature by opening and closing the solenoid valve at the intake of the heating coil.
A stand pipe is installed in each tank by drilling through the bottom glass. The stand pipe can be made in two sections. The whole pipe can be unscrewed for a full 100% drainage or a partial discharge by unscrewing only the top portion.
A pipe of a larger diameter surround the stand pipe. Holes are drilled in it at the end near the tank bottom. Water from the tank is forced to go through these holes, carrying with it the discus feces and other solids to exit the tank through the opening at the top of the inner stand pipe. This outer pipe also serves very conveniently as the spawning cone in the breeding tank.
The water from all the aquarium is returned to the central vat after passing through the biological filter. The filter material is bioball. Several layers of filter floss are placed on top of the bioball which are cleaned daily.
Supersaturated Oxygen System
This is an American technology invented by the US government in the '80s. Please refer to diagram 1 for the construction of a simple oxygen reactor.
Water and oxygen enter the 2 meters tall reactor at the top. The amount of oxygen is regulated by an oxygen meter. The incoming water is dispersed by trickling down a column of bioballs and then exits the reactor at the bottom which is submerged to a depth of 20 cm below the water level in the receiving vat. The reactor must be air tight so that it can be pressurized.
The working principle is that there is 100% oxygen gas inside the reactor but only a few ppm in the aquarium water. Under the pressurized condition in the reactor, water can be supersaturated with oxygen gas up to a concentration as high as 20 ppm.This valve is impossible to achieve under atmospheric pressure.
If pure oxygen is replaced by air, the reactor become a very good biological filter.
Artificial Raising
Benefits
Firstly, there is at least a ten fold increase in productivity to make mass production without the use of drugs a reality.
Secondly, artificial raising conserves the energy of valuable specimens. Discus ages very quickly after feeding its body tissues to its offspring. The process is a tremendous stress that it can never fully recover from, especially when the discus harbours parasites and its vital organs were damaged by drugs.
Thirdly, many valuable strains have very weak larvae that do not have the strength to swim to their parents to feed when they become free swimming. They swim around aimlessly at the bottom of the aquarium and soon die from starvation. This is especially true as inbreeding proceeds in a strain. In the artificial raising process, there is an abundance of food around the mouth of the larva so that there is no need for it to seek for food.
Lastly, artificial raising stops the transmission of parasites having a direct life cycle, such as hexamita, capillaria and gill flukes which are the scourges of all discus in captivity. Discus grows a lot faster when healthy.
Theory of Artificial Raising
In the aquarium, discus larvae always swim to feed on the skin of their parents immediately after becoming free swimming. They only begin to eat other foods after 3-4 days. In their natural habitat, the environment is very different from the peace and tranquillity in the aquarium. It rains almost daily in the Amazon River basin. The deluge creates a lot of noise when the raindrops hit the water surface. It is non-stop for weeks during the wet season. Water level of the river rises for 10-15 meters together with a much stronger current and faster rates of water flow. Flooding of the forest results in an abundance of nutrients in water to allow planktons to multiply rapidly. Discus, as well as other fishes, breeds a lot more frequently to take advantage of the abundant food organisms to feed itself and its offspring. Surrounding the discus pairs are plenty of other fishes which are also breeding, many are as territorial as the discus. There are also predators both inside and above the water. The discus habitat during the wet season in the Amazon River backwater is as hectic as a Persian market. Will the larva die if the parents are eaten by a predator or are driven away by a bigger fish? If the discus larva can only live on its parents' skin, then none of the artificial raising methods will work. But the fact that discus larva can be raised artificially makes me believe some discus larvae do survive in nature on other kinds of food.
History
In the late 1950s or early '60s, Harry Matson in Chicago, USA, already had some success to rear discus larvae away from their parents. A friend, Mr. Swegles, suggested Harry to test the commercial baker's egg yolk powder. Mr. Matson soon succeeded to breed thousands of discus by smearing the egg yolk on the aquarium wall at the water meniscus. In 1961-'63, he published the whole process in the popular tropical fish magazine called "Tropical". Carroll Freswold in Los Angeles, California read Harry's article and started immediately to apply it to breed discus. He also uses the special egg yolk powder made for the bakery industry. The egg yolk is mixed with water and is kneaded into a tacky consistency. It is smeared as a 1-1.5 cm wide stripe onto the inside of a white enamel pan. Water is filled up to this level. The discus larvae are placed into the pan to feed for a few hours and then moved to a new prepared pan to resume feeding or a major water change is made, the egg yolk is reapplied after the old one is removed, water is then added up to the correct level. The whole procedure is repeated several times per day.
Jack Wattley learned everything about artificial raising from Carroll Friswoll but he made some small improvements by adding other ingredients into the egg yolk.
Discus larvae fed on egg yolk grow very slowly. If the raising process is not perfect, the discus becomes deformed and ugly, speccifically, big eyes, a long body form and very short fins. Other breeders who feed the larvae with small organisms such as rotifers and protozoans also have no good results.
The Artemia Method
In 1987 Dick Au, an American discus friend, told me artemia nauplii can be used as the larva food. Success in artificial raising finally came in April, 1990. Artemia nauplii were added to a small tank in abundance so that the larvae bump into the artemia in every direction they swim. The larvae ate the nauplii and grew.
Discus larvae grow a lot faster when feeding continuously under 24 hours light.
Whenever their is a problem, switch the artemia cysts. It may be deficient in nutriets or toxic.