Nutrition is a critical factor in the longevity of decorative fish in aquariums. Since the greater majority of fish are caught in the wild, the aquarist faces the problem of providing foods that are good substitutes for those normally eaten in the natural habitat. The diet must include enough variety to supply the appropriate proportion of nutrients.
Satisfying the requirements of freshwater fish can be sometimes problematic. Many species have strict requirements for only certain types of foods. For example, some species will eat only live foods. There are species of fish that are so specific in their feeding habits that they should never be purchased for a home aquarium. Though the study of freshwater fish nutrition is in its infancy, research to date has provided information on their generalised requirements.
The health and longevity of aquarium fish largely depend on the quality and quantity of the diet. The nutritional needs of fish are not static, but change especially during demanding physiological periods. To ensure normal growth, structural tissue and organ integrity, reproduction, physiological function, and disease resistance, fish must have nutritionally sound diets.
To minimise deficiencies under aquarium conditions, freshwater fish diets must be varied; the diet can include frozen foods, live foods, and prepared dry foods. Each of these types will be examined later.
Food furnishes usable energy for growth, tissue repair, swimming, and other essential activities. The rate at which energy is used, called the metabolic rate, is a function of various factors, including temperature, the species of fish, its body size, and its physical condition.
You must understand that water temperature is the most important factor affecting a fish's metabolic rate. This is due to the fact that a fish's body temperature is always close to the ambient water temperature. Therefore, if the aquarium water is 80 F (26.6°C), the fish's body temperature will also be close to 80°F (26.6°C). As the water temperature increases, so does the metabolism of the fish and its energy requirements.
Aquarium fish also have variable energy requirements depending on the species. In order to maximise growth, young fish require more calories than older fish.