Agricultural Reviews

An element is considered as dietary essential when its absence or insufficiency in diet causes deficiency syndrome and supplementation in normal level brings back normal health. An organism can neither grow nor remain healthy without the element in question. The element should have a direct influence on the organism and involved in the metabolism. Effects of the essential elements cannot be wholly or partly replaced by any other elements. All forms of aquatic inhabitants require some inorganic elements in little or trace amounts for their normal growth and metabolism. Trace minerals do not exist only by themselves but in combination with others. Therefore too much of one element may lead to imbalances in others resulting in disease or adverse effect in metabolism. Factors such as diet, absorption ability, toxicities and drug-nutrient interactions may play a role in maintaining a balance of trace minerals in the animal body. In comparison to the farmed animals, the knowledge on dietary essentiality of minerals in fish is scarce being mainly restricted to iron, copper, manganese, zinc, iodine, selenium, cobalt and chromium as components of body fluids, co-factors in enzymatic reactions, structural units of non-enzymatic macromolecules, etc. Investigations in fish are comparatively complicated as both dietary intake and its uptake from availability in water have to be taken in account for determining the total mineral budgets. The importance of trace minerals as essential ingredients in diets, although in small quantities, is also evident in fish. Though requirements of trace minerals have been studied in some species, still research work needs to be intensified for other freshwater fish species.