Improving the survival, growth and hemolymph ion maintenance of early juvenile blue swimmer crabs, Portunus pelagicus, at hypo- and hyper-osmotic conditions through dietary long chain PUFA supplementation

Abstract

Blue swimmer crab, Portunus pelagicus, juveniles are weak osmoregulators leading to reduced survival and growth outside salinities of 15–35‰. Therefore improving the performance of this commercially important crab at sub-optimal salinities through diet manipulation will likely benefit the aquaculture industry. The aim of the current experiment was to determine whether increased dietary LC-PUFA, in the form of fish oil, could improve the survival, growth and hemolymph ion maintenance of early P. pelagicus juveniles at salinities of 14, 30 and 42‰. Crabs were fed five diets containing 0, 3, 6, 9 and 12% fish oil inclusion levels (% dry diet weight) and their survival and growth were measured over 20days. After 20days, the hemolymph Na+, K+ and Ca2+ levels of the crabs were measured. Seven replicates, with three crabs in each replicate, were used in each salinity/dietary treatment (total of 315 crabs). Results showed diets containing 0% fish oil inclusion led to the lowest survival in all salinities, although this was only significant (p<0.05) for the crabs cultured at a high salinity of 42‰. Further, a salinity of 42‰ generally caused lower growth, compared to 14 and 30‰, however the highest fish oil inclusion level of 12% (or 3.73% LC-PUFA) caused no significant growth or development difference (p>0.05) compared with those fed the same diet but at a salinity of 30‰. Between salinities of 14 and 30‰, no significant growth difference was detected although the growth benefit to increased dietary LC-PUFA at 14‰ was more obvious than at 30‰. Meanwhile, at salinities of 14 and 42‰, hemolymph Na+ regulation was significantly improved through dietary LC-PUFA supplementation, indicating that LC-PUFA is an essential nutrient for undisrupted ion-regulation. These findings indicate that the productivity of P. pelagicus juveniles may be increased at sub-optimal salinities through dietary LC-PUFA supplementation, which may be linked with improved hemolymph ion maintenance.