Introduction

The feeding of rainbowfishes is one of the most important factors in keeping them healthy. In captivity, maintaining good health and growth in your rainbowfishes depends directly on the quality and quantity of the nutrients received through their daily diet.

Rainbowfish keepers determined to raise and maintain the finest specimens must provide a nutritionally balanced diet for their rainbowfishes throughout their entire life cycle. Obviously, no single food will meet their needs at all life stages, and the best way to ensure that they are getting a well-balanced diet is to feed them as wide a variety of food as possible.

Rainbowfishes can generally be classed as omnivorous as they have intestinal tracts that can digest both animal and vegetable material. They are opportunistic feeders and can be seen around sub-surface aquatic vegetation feeding on a variety of terrestrial insects, small aquatic crustaceans, insect larvae, worms, phytoplankton, zooplankton, aquatic plant material, detritus (inanimate suspended matter principally of organic origin), and where the opportunity occurs, smaller fish will also be consumed. The size and variety of their diet can differ widely from one species to another and from one habitat to another.

The best food for rainbowfishes in captivity is of course, to duplicate their natural diet. To give you some idea of their natural diet, a stomach analyses taken from a sample of rainbowfishes showed that their diet consisted of 40% terrestrial insects, 37% small aquatic crustaceans, 18% aquatic insects and 5% algae, pollen, seeds and miscellaneous organic matter. Scientific data from stomach content analyses in wild populations can be helpful in selecting the right type of diet for your fishes. However, it is unlikely that you will be able to match that diet in captivity.

Rainbowfishes in the wild, particularly the Australian species, usually exist under feast or famine conditions, which relates to the prevailing season. The season of greatest feeding activity in tropical rivers is the wet season. Feeding activity increases most dramatically between the late-dry season and the early-wet season. By the mid-wet season feeding activity had peaked, and then decreased slightly by the late-wet to early-dry season. An examination of variations in body condition indicated that most species obtained their best condition from the mid-wet to the mid-dry season, with a peak in the late-wet early-dry season. During the dry season, when the water volume of their habitat is greatly reduced, the only food they get is whatever happens to fall into the water.

Under aquarium conditions we normally have to rely on "unnatural" foods. Therefore it is necessary to provide favourably aquarium conditions and careful feeding with specially formulated diets in an attempt to satisfy all their nutritional requirements. Rainbowfish can be maintained on a diet consisting totally of manufactured dry foods such as flakes, pellets and granular formulations. The better known brands have been formulated so that the basic nutritional content is at the proper levels. Such feeds however, need to be not only nutritious and palatable, but also capable of floating or sinking slowly. Rainbowfishes are primarily surface feeders so feeds that sink too quickly will become wasted in the gravel substrate.

All fish species in our care require a balanced diet and for best results, some live or frozen foods such as bloodworms, whiteworms, daphnia, mosquito larvae, moina etc., should be an integral part of feeding. 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 (you wouldn't like to eat frozen food for dinner, would you?). Many frozen foods available from aquarium suppliers contain a lot of water or processing liquid and this has no nutritional value at all and will only pollute your aquarium. If you are in a hurry, as most of us are these days, then place the frozen food in a sieve or strainer and run it under the cold water tap. You may be surprised just how much food is left for feeding.

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.

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.

Live foods are not necessary but if you have access to them then this is by far the best food that you can feed to your fishes. However, most of us do not have that luxury so other forms of foods must be found. 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. I do not like to feed my fish with animal meats as these meats are normally very high in saturated fats. Saturated fats are not easily digested by fish and I believe they are detrimental to the long term health of rainbowfishes or for that matter, any aquarium fish. Experiments on fats required by fish have revealed a need for omega-3 fatty acids. These are normally available in fish or other seafood. You can supplement the formulated mixture with live foods, and a good quality bite-sized pellet.

Feeding research has shown that fish need a wide range of essential nutrients to remain healthy. Without the right amount of nutrients, fish may cease to grow, lose colour, stop breeding, become susceptible to disease and, in certain circumstances, might even die. Due to advances in the aquacultural industry, the nutritional requirements for feeding commercial food fish species are well documented. Nevertheless, there are still many unanswered questions when it comes to the nutritional requirements of rainbowfish species. Feeding trials with other aquarium fish have shown 30 to 35% digestible protein is sufficient. However, not all proteins are easily digested and utilised by fish. The quality and digestibility of the protein present in fish food is therefore critically important.

In captivity, rainbowfishes are inclined to overeat and one has only to observe rainbowfishes in the wild to realise that most captive specimens are overfed and overweight. If fed the wrong sort of foods (those rich in saturated fats) they are prone to obesity and may develop lipodosis (fatty degeneration of the internal organs) and eventually die. Experiments on fats required by fish have revealed a need for omega-3 fatty acids. These are normally available in fish or other seafood.

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 function of foods and feeding will help in the choice of the most suitable commercial food available for your aquarium fishes or in formulating your own mixture.

© Copyright Adrian R. Tappin
Updated July, 2005.