OXYGEN-CONSUMPTION AND AMMONIA EXCRETION OF PENAEUS-SETIFERUS, P-SCHMITTI, P-DUORARUM AND P-NOTIALIS POSTLARVAE FED PURIFIED TEST DIETS - EFFECT OF PROTEIN LEVEL ON SUBSTRATE METABOLISM

Taking into account that the relationship between metabolic substrate and the characteristics of the diet is essential for understanding the mechanisms associated with the use of the components of a certain foo d substance, the aim of this study was to examine the metabolic substr ate used by Penaeus setiferus, P. schmitti, P. duorarum and P. notiali s postlarvae PL 35-40 (35-40 days after metamorphosis) fed purified di ets with different levels of proteins (40, 50, 60 and 65%). Oxygen con sumption and ammonia excretion were measured in animals in intermoult which had been acclimatized to each diet over a minimum of 5 days. Mea surements were taken on fasted (24 h) and fed animals. Oxygen consumpt ion of fasting animals increased with a rise in the proteins of the di et in the four species. In the fed animals, this tendency was observed in P. setiferus and P. notialis, while in P. schmitti and P. duorarum oxygen consumption was a weak relationship, decreasing or increasing with a diet with 50% protein. Both in fasting and feeding animals, the ammonia excretion increased with the increase in proteins in the diet . The O:N atomic ratios of the four species decreased (between 30 and 3), according to increase in dietetic protein:energy ratio, (10.4 to 1 7.0 mg protein/kcal). The highest value of O:N ratio was observed in P . setiferus (40% of protein requirement, O:N=24 to 34) and lowest in P . schmitti (60% of protein requirement, O:N=4 to 11), with intermediat e values in P. duorarum and P. notialis (50% protein requirement, O:N= 8 to 14 and 13 to 19, respectively). These results support previous re search that showed that the omnivorous-herbivorous species, like P. se tiferus, use protein-lipids normally as energy source in contrast to o mnivorous-camivorous species such as P. duorarum which use protein pre ferentially as a source of energy.