Although ornamental fish have been kept for more than three centuries, the feeding of aquarium fishes is mainly based on calculations of nutrient requirements and practices derived from food fish under intensive cultured conditions aimed at maximum growth in a short time period. This might be of value for the commercial farming of ornamental species, but would be unsuitable for fish kept in home aquaria.
The formulation of adequate diets for organisms in an aquatic environment gives a greater challenge to those involved in their care, compared to terrestrial species. In general the maintenance energy requirement of fish is <10% of the maintenance energy required by birds or mammals. The low maintenance energy requirement is partly due to the poikilothermic nature of fish. Fish also exert less energy on posture and have an energetic advantage over mammals in their nitrogenous waste management as they excrete mainly ammonia instead of urea or uric acid, thus losing less energy in protein catabolism and excretion of nitrogenous waste. The provision of energy and other nutrients to poikilothermic animals can take many forms and is generally chosen by reference to their natural ecology. However, it is pertinent to note that feeding diets high in protein to herbivorous and omnivorous fish may result in increased tank pollution with no real gain in food utilisation. Feeding strategies and anatomical differences between fish species make formulation of one diet for a community of species quite difficult.
Some research on the nutritional requirements of freshwater ornamental species (live-bearers) in a production environment has been conducted, mainly in Singapore. Protein requirements varied from around 30% dietary protein for growing omnivorous goldfish (Carassius auratus) to 50% for the carnivorous discus (Symphysodon aequifasciata). Whereas, mineral (phosphorus, iron, magnesium, zinc) requirements have received some attention in feeding Poecilia reticulata, few researches have concentrated on vitamin requirements of ornamental species. Maintenance energy levels of ornamental fish varied from 0.068 kJ per day for Paracheirodon innesi to 0.51 kJ per day for Trichogaster microlepis, kept at a water temperature of 26°C. However, large commercial producers of aquarium fish in Singapore emphasise the importance of regular supplementation of formulated feeds with live feed, as the inclusion of live feed improves growth.
For general aquarium maintenance, most of the commercial feeds are adequate. However, it is advisable to give your rainbowfishes an occasional feeding of green food. A lack of green food is detrimental to their health. The best, because it is the most natural, is duckweed (Lemnaceae). Duckweed has higher concentrations of the essential amino acids, lysine and methionine, than most plant proteins and more closely resembles animal protein in that respect. Newly harvested duckweed contains up to 43% protein by dry weight with little to no indigestible material. Cultured duckweed also has high concentrations of trace minerals and pigments, particularly beta-carotene and xanthophyll that make duckweed an especially valuable supplement for rainbowfishes. The fairly high concentrations of these pigments deepen the overall body colouration of rainbowfishes. Duckweed can also be a rich source of ascorbic acid (2.78~4.90 mg/100 grams dry weight). The smaller species like Wolffia and Lemna are better for rainbowfishes and most will eat it avidly. When this is not available good substitutes are boiled and finely chopped spinach or zucchini.
It has been shown that duckweed is very efficient in removing ammonia and other dissolved nutrients from the aquarium water. Research results suggest that approx. 50% (± 20 %) of the total nitrogen load is assimilated by duckweed. However, duckweed produce spreading floating masses of foliage, and if not introduced with some caution, can become a nuisance, carpeting the surface of the pond or aquarium, excluding light, and causing the submerged aquatics beneath to deteriorate or die out. As with most free-floating aquatic plants they are not stable in the water, drifting around, and under heavy aeration they can form into floating masses on the perimeter of the aquarium or pond.
In a well-established planted aquarium, rainbowfishes will always fine some green food among the aquatic plants, but a feed of duckweed, or spinach, at least once or twice a week is to be recommended. If duckweed is taken from natural waters it should be thoroughly cleansed before giving it to the fish. Failure to take this precaution may result in undesirable parasites being introduced into the aquarium.
To keep rainbowfishes in foremost breeding condition you should be aware that nutritional deficiencies may exist in prepared foods. An ideal aquarium diet for rainbowfishes could include foods such as live and frozen daphnia, bloodworms and other aquatic invertebrates, chopped fish or shrimp, blanched zucchini, spinach and duckweed. Spirulina-based foods, flake, and bite-sized pellets designed for ornamental fishes are also acceptable. Avoid feeding large amounts of dried feeds developed for the aquaculture industry, which can cause health problems in rainbowfishes over the longer term.
Freeze dried foods are another type of food that can be fed to rainbowfishes. The process of freeze-drying is to remove only the water content, leaving the nutrients content intact. If you feed freeze dried foods all the time then it would be best to pre-soak them in water before feeding to your fishes.
Frozen foods can be a more natural source of nutrients than dry manufactured foods. When feeding frozen foods, always thaw them to room temperature before feeding your fishes. Many frozen foods available from commercial suppliers often contain liquefied nutrients or processing water that may pollute the aquarium water and contribute to bacterial growth when thawed. The best way to defrost frozen foods quickly is to place the frozen food into a strainer and run it under a cold water tap. This will also wash away the dissolved nutrients or any processing liquid that will remain uneaten if fed to your fishes. Although freezing does not significantly alter the nutritional content, nutrients do leach out rapidly into the water. Nearly all of the enzyme activity is lost within ten minutes after introduction into water. After one hour, all of the free amino acids and many of the bound amino acids are lost.
Care must be taken to overcome the leaching properties of certain foodstuffs, especially in aquariums, where the volume of water is small. Once the nutrients are released from the diet into the water they are lost to the fish. Any vitamins or nutrients that are leached into the water are not known to be taken up through the skin or gills by freshwater fish species which, in a hypo-osmotic environment, do not drink.
I formulate my own food mix which is a gelatine-based blend consisting of about 90% equal portions of fresh/frozen whitebait, shrimp, and mussel plus about 10% of beef liver and spinach. Small additions of other items such as dried mosquito larvae or similar dried foods, spirulina, fish roe, and a host of other gourmet delights can be added to the mix. Food sources of marine origin are often utilised in fish foods because they are an excellent source of essential amino acids, fatty acids, vitamins and minerals, and because they generally enhance palatability.
Vitamin supplementation is not necessary. Water-soluble vitamins are most vulnerable to nutrient leaching. A large percentage of B-complex vitamins and vitamin C are lost in water within 30 seconds of feeding some commercial flake diets. Fat soluble vitamins such as A, D, E, and K may cause problems if given in large doses. However, over supplementation with the aim to overcoming vitamin degradation and leaching should be avoided to limit the risk of hypervitaminosis. Although, overdose of most vitamins is unlikely to occur as excess vitamins are removed from the body via the kidneys. Brewers yeast, cereals, fish liver and various fish meats and oils contain most of the essential vitamins when fresh, and are key ingredients in most formulated foods. The quality of ingredients in the food will have an effect on the adequate delivery of key nutrients to the fish especially in relation to all the water-soluble components of the diet.
The formulation of a nutritionally balanced diet for your rainbowfishes requires efforts in research and evaluation. Inadequate nutrition obviously impairs fish growth and reproduction, and can result in deterioration of health until recognisable diseases ensue. The borderlines between reduced growth and diminished health, on the one hand, and overt disease, on the other, are very difficult to define. There is no doubt that as our knowledge increases, the nature of the departures from normality will be more easily explained and corrected. However, the problem of recognising a deterioration of performance in its initial stages and taking corrective action will remain an essential part of the skill of the aquarium hobbyist.
The first consideration for the formulation of a successful diet is the quality of the feed ingredients. Diets produced with poor quality raw materials and under adverse processing conditions have inferior nutritive value and adverse effects on fish health. The composition of the ingredient obviously plays a determinant role in the quality. However, biological aspects, such as digestibility and utilisation of nutrients are most important and often overlooked.
The use of a good quality food will provide the fish with all the nutrients that they need to remain healthy and to grow. However, you should note that even good quality food will deteriorate if improperly stored or kept too long. Storage time for most commercial fish foods will vary depending upon environmental conditions; however, as a rule of thumb, 90 days is normally the maximum safe storage time for fish feed. Fish foods should be stored in a cool and dry place (refrigerator), and used within 30 days of opening, particularly in hot, humid climates. Never feed mouldy, discoloured or clumped feed. Moulds on feed may produce aflatoxins, which can kill fish. Only buy large containers of food if you have a large number of fish.
Whatever choices you make regarding feeding your fishes, remember that variety is not only the "spice of life", but is the best way to provide them with the essential nutrients to give energy and build tissue. With proper feeding and aquarium management, most rainbowfishes will have the opportunity to live a longer life in captivity than they would in the wild. A reasonably knowledge of the nutritional value of foods will therefore help in the choice of the most suitable food available for your rainbowfishes or in formulating your own mixture.
Literature
Cowey, C. B. and C. Young Cho (1993) Nutritional requirements of fish. Proceedings of the Nutrition Society 52:417-426.
Hillman, W.S. and Culley, D.D. (1978) The Uses of Duckweed. American Scientist, 66: 442-451.
Leng, R. A., Stambolie, J. H. and Bell, R. (1995) Duckweed a potential high protein feed resource for domestic animals and fish. Livestock Research for Rural Development Vol.7, No.1, New England.
Pannevis, M. C. and K. E. Earle (1994) Nutrition of Ornamental Fish: Water Soluble Vitamin Leaching and Growth of Paracheirodon innesi. Journal of Nutrition 124: 2633S-2635S.
Pannevis, M. C. and K. E. Earle (1994) Maintenance Energy Requirement of Five Popular Species of Ornamental Fish. Journal of Nutrition 124: 2616S-2618S.
Sales, J. and G. P. J. Janssens (2003) Nutrient requirements of ornamental fish. Aquatic Living Resources 16: 533-540
Tacon, A.G.J. (1987) The nutrition and feeding of farmed fish and shrimp - A training manual 1: The essential nutrients. Food and Agriculture Organization.
© Copyright Adrian R. Tappin
Created December, 2008.
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