Summary
The development of commercially manufactured fish food could be considered as one of the contributing factors to the tremendous growth of the aquarium hobby over the past 50 years. However, most information on the nutrient requirements of aquarium fish is derived principally from research carried out by the aquaculture industry. These results do however, have limitations in their applicability for feeding rainbowfishes because it is based on intensive cultured conditions aimed at maximum growth in a short time period. This might be of value for the commercial farming of aquarium species, but would be unsuitable for rainbowfishes kept in home aquaria.
Not only do rainbowfishes have different nutrient requirements, but also the digestibility of various components of the diet will differ depending on their natural diet. In nature, rainbowfishes feed mainly on aquatic insect larvae, microcrustaceans, food from terrestrial origin (mainly terrestrial insects), and many other items that they encounter in their environment. When confined to an aquarium these supplemental food items are no longer available.
In captivity their survival dramatically depends on exogenous food. Hence, complete and balanced nutrition is critical for their wellbeing. However, despite the wide range of food items consumed in their natural diet, under aquarium conditions they are forced to feed on a very limited number of food items (two or three) which frequently are not part of their natural food and hence their nutritional composition is not always the most suitable for maximum growth, development and survival.
The nutritional requirements of most rainbowfish species is poorly understood. Rainbowfishes are essentially omnivorous and for this reason, it is a good management practice to feed a variety of foods to captive fish. Omnivores, by definition, eat a wide variety of food items including plant and animal material, and some detritus as well. Physical characteristics of the diet also play an important role. Food particles need to be small enough for the smaller species to ingest, but large enough to be identified and eaten by the larger species. The availability of a suitable diet is critical for successful transition of larvae to juvenile and juvenile to adult stages.
Moreover, the development and survival of rainbowfishes in the wild undergo several morphological and physiological changes which in nature are simultaneous with changes in behaviour and even habitat and type of food consumed. All these changes will affect the nutrient availability and feed utilisation by the fish in order to match their nutritional requirements. In practice, most of these problems could be simplified by the proper development of inert diets which are able to cover nutritional requirements at different stages of development. In order to achieve those diets we need, among many other important things, is to have a complete knowledge of the nutrient requirements for the different rainbowfish species.
Unfortunately, most hobbyists do not research the fish they keep, and consequently, do not provide an appropriate diet for the species they are trying to maintain.