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   While the total nutritional requirements of fish are still largely unknown, some generalizations can be made to help the hobbyist in the selection of foods for tropical fish. 

   Let's review what is known about the nutritional requirements of fish. All nutrients necessary for health can be categorized as protein, fats, carbohydrates, vitamins, minerals or water. Water is rarely a problem nutritionally for fish because of its absorption from the environment. Vitamins and mineral requirements are virtually unknown for most fish, and are assimilated through the gill membranes rather than introduced with foods. For this reason, we look to the natural mineral content of water to supply the necessary vitamins and minerals. 

Proteins make up most of the body tissues of fish. When ingested, they are converted to amino acid compounds which are used for energy and to build new proteins and tissue. It has been found that protein levels from 36% to 60% are the most adequate for the growth of fish. 

Fats, both solid and liquid oils, supply twice the energy of proteins and are stored in tissues for reserve energy. Solid-type fats are not effectively used by fish. However, most liquid oils are readily digested and used. Rapidly growing fish like cichlids use oils over carbohydrates for their energy. Optimum levels of fatty oils range from 15% to 25%. The presence of oxygen reacts with oils, turning them rancid and unusable. It's reasonable to believe breeder fish need even higher levels of oils in their diets since eggs are mostly stored oil. 

Carbohydrates may be in the form of starches or sugars. Starches are not easily digested and are not used for energy by most fish. Low levels of sugar are utilized best by fish. Less than 10% is recommended. 

In nature, fish feed on a wide variety of organisms to assure they get all their nutritional requirements. Know fishes' eating habits. Do they feed at the surface level or bottom, and are the predators insect feeders or herbivores (vegetarians)? 

There are four basic rules of fish feeding: 

1) Tailor a diet to the fishes' natural food.

 2) The more you demand of the fish, the better nutrition the fish will require. 

3) Be aware of deficiencies resulting from processing. 

4) Feed as varied a diet as possible.

   In order to choose among the forms of fish food, we need to examine the pros and cons of each: 

Flake foods: Dry flake foods are popular because they are easy to use and store. They are adequate for most fish nutrition needs, providing proteins, carbohydrates, vitamins and minerals. However, vitamins may be destroyed if excessive heat is used during processing. Since oils rapidly turn rancid when exposed to oxygen, they are not present in dry foods in quantities high enough to provide optimum nutrition. Also, carbohydrate levels are often too high. 

Freezing: This method efficiently and effectively preserves all the nutrients present in the organism(s) being processed. The nutritional benefit of the frozen product will be limited only by the natural content of the live food. For example, brine shrimp are deficient in vitamin A, so this deficiency is present in frozen shrimp. Freezing is the best method of preserving oils. Because some people object to the storage of such products in the home freezer, keeping these foods may not be practical. 

Freeze-drying: This method preserves all the natural nutrients present in the organism except fats (oils). As with dry foods, contact with oxygen during or after processing turns oils rancid. Again, some nutrient deficiencies may exist due to deficiencies in the food being processed. Freeze-dried foods are easy to store, although expensive to purchase. 

Live food: Live foods contain all the nutrient classes including oils. As stated previously, deficiencies may be present in individual foods. However, since fish are instinctively attracted to live food, they tend to eat more and receive better nutrition. Unfortunately, culturing a variety of live food is difficult because of the time and expertise required. If purchased, live foods are often very expensive and the supply can be undependable. In conclusion, we find there is no single perfect food or method of preservation. For this reason, we should feed as wide a variety as possible, using as many forms of food as we can.


 -Many thanks to Biotope Research for their assistance with this article.

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