Effects of dietary protein level on growth and utilization of protein and energy by juvenile haddock (Melanogrammus aeglefinus)

초록

In order to determine the optimum level of protein required in the diet of juvenile haddock, 750 fish with an average weight of 6.9 g were randomly distributed into each 15 tanks (320 1). Haddock were fed one of five isoenergetic diets containing 45%, 50%, 55%, 60% and 65% protein to satiation. All fish fed the experimental diets for 6 weeks had more than a three-fold increase in body weight, although no significant difference in weight gain was found among treatments. Feed/gain ratio decreased from 0.76 for fish fed 45% protein to 0.62 for fish fed 65% protein. Nitrogen (N) intake increased with an increase in dietary protein, which, in turn, resulted in an increase in N gain of fish whole body. Fish fed 45% protein gained 0.37 g N, which was not significantly different from that of fish (0.40 g) fed 50% protein. Nitrogen gain for fish fed the remaining two diets (55% and 60% protein) had the same value (0.43 g); that was significantly (P < 0.05) higher than fish fed the diet containing 45% protein. The broken-line regression of N gain against dietary protein level yielded an estimated protein requirement of 53.8% (Y = 0.43 - 0.006(R - X<inf>LR</inf>), R = 53.8 ± 2.08) on a dry-matter basis. Gross energy intake of fish varied from 283 to 229 kJ for fish fed 45% and 65% protein, respectively. The highest energy gain of 119 kJ was obtained with fish fed 50% protein, resulting in the highest energy retention efficiency of 44.1%. The hepatosomatic index of fish significantly (P < 0.05) decreased from 10.7% to 7.3% as dietary protein level increased. © 2001 Elsevier Science B.V.

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