Minerals (OTHER ESSENTIAL INORGANIC ELEMENTS)

Dietary requirements of fish for most of the trace mineral elements have not been established. Iron deficiency in the red sea bream results in a form of microcytic, hypochromic anaemia similar to iron deficiency anaemia in land animals. Common carp fed a semi-purified diet without supplementary iron grew normally but exhibited sub-clinical symptoms of hypochromic microcytic anaemia. Iodine deficiency produces a goitrous condition in trout. Rainbow trout fed a semi-purified diet deficient in zinc (1 ppm) had increased mortality rate, cataracts in the eyes and erosion of the fins and of the skin. Protein digestibility was also reduced. Manganese has also been shown to be essential for growth and survival of Tilapia mossambica and the rainbow trout.
The roles of trace elements in fish, although not clearly defined, are probably similar to those described for land animals. Fish in their natural habitats are probably adequately provided for to meet the requirements for all the mineral elements. However, the intensive culture of certain fish species in man-made ponds and raceways, together with reliance on artificial feeding, make it necessary to incorporate adequate quantities of mineral nutrients in the feed. For the most part, where exact requirements are not known, levels are arbitrarily based on land animal requirements.