THE EFFECT OF DIETARY-PROTEIN CONTENT ON GROWTH, DIGESTION EFFICIENCYAND NITROGEN-EXCRETION OF JUVENILE KURUMA PRAWNS, PENAEUS-JAPONICUS

The effect of dietary protein contents on growth, digestion efficiency and ammonia and urea excretion of juvenile kuruma prawns, Penaeus jap onicus, was investigated. Isocaloric, crab-protein-based, dry diets co ntaining five protein contents (21 to 61%) were formulated and fed to prawns (initial mean wet wt 0.4 g) at a ration level of 6% body weight per day for 30 days. At the end of the trial, intermolt-staged prawns (0.5 to 2.0 g wet weight) were used for determination of digestion ef ficiencies for dry matter and protein, and ammonia and urea excretion rates. Weight gain, specific growth rates (SGR) and feed conversion ef ficiency (FCE) values for prawns fed diets containing 21 and 31.4% pro tein were significantly lower than those for prawns fed diets containi ng higher protein contents. There was no significant difference in wei ght gain, SGR and FCE values among prawns fed the 41.6, 50.3, and 60.7 % protein diets. Digestion efficiencies for dry matter and protein ran ged from 73 to 77% and 93 to 96%, respectively. After a 1-h feeding pe riod, cumulative ammonia excretion over a subsequent 5-h period increa sed with increasing dietary protein content, and ammonia excretion rea ched a peak within the first 3-h period in all treatment groups. In co ntrast, ammonia excretion rates of prawns initially fed on diets with different protein contents then starved for 24 h, were constant at abo ut 10 mug/g h-1, indicating that a 24-h starvation period eliminated d ifferences in ammonia excretion rates due to variation in dietary prot ein content. Urea excretion rates were much lower than ammonia excreti on rates in this species. Results indicated that 42% dietary protein s ustained maximum growth of kuruma prawns under the conditions employed in this study, and that there was a positive correlation between SGR and ammonia excretion for juvenile P. japonicus.