Effect Of Dietary Protein Level On Nutritional Modulation Of Penaeid Shrimp Reared At High Salinity

The effect of salinity on growth and survival of Litopenaeus vannamei, Fenneropenaeus chinensis and Penaeus monodon postlarvae were first investigated. The results showed that L. vannamei was able to tolerance higher salinity (salinity of45) and thus is a suitable candidate aquaculture species in hypersaline environment. Based on the above results, the effects of salinity and dietary protein level on growth and survival of L. vannamei were further conducted. And the nutritional and physiological modulating mechanism was also discussed. The aim of this study was to provide the useful information on optimizing the dietary formulation for L. vannamei cultured in hypersaline environment.A70-day trail was conducted in indoor condition, to compare the growth and survival of L. vannamei, F. chinensis and P. monodon postlarvae in culture medium with salinity of30and45, respectively. Postlarve of three Penaeid species were fed formulated feed containing36.8%protein. The growth and survival of L. vannamei at both salinities were significantly higher than those of F. chinensis and P. monodon (P<0.05), indicating that L. vannamei was more tolerance to the hypersaline environment.A40-day trail was conducted to investigate the effects of salinity (0,30and60, respectively) and dietary protein levels (35%,40%,45%and50%, respectively) on the growth and survival of L. vannamei postlarvae. And the approximate biochemical composition (i.e. moisture content, ash content, crude protein and soluble protein content), enzymatic activities and amino acid composition of the shrimp muscles were analyzed. The results showed:1) Salinity had significant effect on growth and survival of L. vannamei postlarvae. Survival rate was the highest at salinity60and the lowest at salinity0, whilst that at salinity30was in between (P<0.05), which might be attributed by the less ammonia concentration and lower density of pathogenic bacteria in culture medium at salinity60. Growth performance (i.e. individual body weight, body length, weight gain rate and special weight gain rate) at salinity60were significantly lower than that of other two groups (P<0.05), assuming that it should be attributed by the extra energy consumption on osmoregulation.2) Dietary protein level significantly affected the growth performance and survival of L. vannamei at both salinities. The growth performance increased with the increasing dietary protein from CP30to CP45, but decreased slightly at CP50(P<0.05), meaning that the optimal dietary protein level was45%under the experimental conditions.3) Although there was no statistically significant difference among the treatments, relative activity of glutamic oxalacetic transferase (GOT) in shrimp muscles at salinity60was higher than those of other two groups, while relative activity of catalase (CAT) was lower than those of other two groups, indicating that L. vannamei cultured at salinity60were likely exposed in stressful condition. Furthermore, crude protein content and total amino acid content and composition (especially glutamic acid, aspartic acid, lysine and serine) in shrimp muscles at salinity60were higher than those of other two groups, showing that L. vanmimei cultured in hypersaline condition had higher nutritional value and better taste.