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.
A summary of available information on mineral requirements of fish is given in Table 1.
|Mineral element||Principal metabolic activities||Requirement symptoms||Requirement / kg dry diet|
|Calcium||Bone and cartilage formation; blood clotting; muscle contraction||not defined||5g|
|Phosphorus||Bone formation; high energy phosphate esters; other organo-phosphorus compounds||Lordosis, poor growth||7g|
|Magnesium||Enzyme co-factor extensively involved in the metabolism of fats, carbohydrates and proteins||Loss of appetite, poor growth, tetany||500 mg|
|Sodium||Primary monovalent cation of inter cellular fluid; involved in acid-base balance and osmoregulation||not defined||1-3g|
|Potassium||Primary monovalent cation of intra-cellular fluid; involved in nerve action and osmoregulation||not defined||1-3g|
|Sulphur||Integral part of sulphur amino acids and collagen; involved in detoxification of aromatic compounds||not defined||3-5g|
|Chlorine||Primary monovalent anion in cellular fluids; component of digestive juice (HCl); acid-base balance||not defined||1-5g|
|Iron||Essential constituent of haeme in haemoglobin, cytochromes, peroxidases, etc.||Microcytic, homochronic anaemia||50-00 mg|
|Copper||Component of haeme in haemocyanin (of cephalopods); co-factor in tyrosinase and ascorbic acid oxidase||not defined||1-4g|
|Manganese||Co-factor for arginase and certain other metabolic enzymes; involved in bone formation and erythrocyte regeneration||not defined||20-50 mg|
|Cobalt||Metal component of cyanocobalamin (B12). Prevents anaemia; involved in C1 and C3 metabolism||not defined||5-10 mg|
|Zinc||Essential for insulin structure and function; co-factor of carbonic anhydrase||not defined||30-100 mg|
|Iodine||Constituent of thyroxine; regulates oxygen use||Thyroid hyperplasia (goiter)||100-300 mg|
|Molybdenum||Co-factor of xanthine, oxidase, hydrogenases and reductases||not defined||(trace)|
|Chromium||Involved in collagen formation and regulation of the rate of glucose metabolism||not defined||(trace)|
|Fluorine||Component of bone appatite||not defined||(trace)|