Growth and tissue mineralisation of Atlantic cod (Gadus Morhua) fed soluble P and Ca salts in the diet

Triplicate groups of 150 g Atlantic cod juveniles (Gadus morhua) previously fed a phosphorus (P) depleted diet for 19 days, were fed 1 of 6 experimental diets with variable P and calcium (Ca) supplementation levels for 91 days. Fish muscle meal, low in P and Ca, was used as basal protein raw material in the diets, whereas additional P and Ca were supplemented as soluble minerals (KH2PO4, NaH2PO4, CaSO4). Diets 1 (D1) and 2 (D2) were not supplemented with P. Diet 3 (D3) was supplemented with 0.3% P and diets 4 (D4) and 5 (D5) with 0.6% P. D2, D3 and D4 were supplemented with 0.88% Ca. Fish from all diets at least doubled their weight during the experiment, but no significant differences in daily growth or feed intake were found among the different treatments (P > 0.05). With increasing dietary supplementation of P, significant increase in fork length (P < 0.05) and a tendency for higher growth rate and improved feed efficiency was observed. Calcium supplementation had no effect on growth rates, feed efficiency or P utilisation efficiency. Dietary P and Ca supplementations significantly affected whole body and vertebrae proximate composition, fish morphometrics and apparent digestibility coefficients (ADC) of protein, lipid, energy, P, Mn, Fe, Ca and Se (P < 0.05) and further significantly affected macro- and micro-mineral status in whole body and vertebrae, but not in plasma. A large number of deformed fish were identified by radiography, but there were no significant differences in the occurrence of vertebral deformities between dietary groups. However, it was obvious from the X-rayed fish that all fish fed the P deficient diets had poor bone mineralisation status whereas all those fed the P supplemented diets had apparently adequate bone mineralisation status.