Growth, survival, and osmo-ionic regulation in post larval and juvenile Indian white shrimp, Penaeus indicus, reared under three levels of salinity in a semifloc system

Three sets of experiments were conducted to determine the short- and long-term effects of salinity (3, 25, and 48 ppt) on the post-larval (PL), nursery, and grow-out phases of Penaeus indicus. In Exp I, the salinity acclimation (3 or 5 ppt day- 1) effects on the survival of PL4 and PL12 were studied at 3, 25, and 48 ppt. In Exp II, nursery rearing (30 days) of PL12 (0.02 & PLUSMN; 0.01 g) was carried out at 1000 PL m � 3. In Exp III, the long-term effects of salinity on osmo-ionic regulatory mechanism of P. indicus juveniles (0.40 & PLUSMN; 0.05 g) was studied at 200 PL m � 3 in a semifloc system for 50 days. Exp I revealed that early PL (PL4) was best acclimatized at 25 (79-81%) followed by 3 (61-62%) and 48 ppt (54-56% survival) with no significant effect (p > 0.05) on the rate of acclimation (3 and 5 ppt day � 1). Similarly, the advanced PL (PL12) exhibited the highest survival (p < 0.01) at 25 (97 & PLUSMN; 9%), followed by 3 (87 & PLUSMN; 2%) and 48 ppt (81 & PLUSMN; 3%). However, in Exp II, the final body weight (0.23-0.29 g) or survival (74-89%) did not vary (p > 0.05) among the treatments. In Exp III, the juvenile P. indicus recorded the highest (p < 0.01) final body weight at 25 (3.2 & PLUSMN; 0.3 g), followed by 3 (3.0 & PLUSMN; 0.6 g), and 48 ppt (1.9 & PLUSMN; 0.1 g). The serum osmolality of juvenile shrimps (270 to 1400 mOsm/Kg) was a positive linear function of medium osmolality (128-1604 mOsm/Kg). The serum ionic profile, muscle moisture content, microbial and microalgal communities varied (p < 0.05) among the treatments. The immunofluorescence assay could localize higher Na+, K+-ATPase reactive cells on the shrimp gill at 3 and 48 ppt. The histological architecture of the hepatopancreas exhibited enlarged and increased B cells (p < 0.01) at higher salinity (48 ppt). The present study suggests that although P. indicus had the best performance at 25 ppt, the shrimp can effectively osmoregulate and cope with wide salinity fluctuations (3 to 48 ppt) through physiological and functional adaptations.

Automated summary

This study examined the effects of salinity on the post-larval, nursery, and grow-out phases of Penaeus indicus through three sets of experiments. The results showed that the larvae adapted best to 25 ppt, and the juvenile shrimp also performed best at 25 ppt. However, different salinity levels had significant effects on the growth, ion concentration, and organ structure of the shrimp in the nursery rearing and osmo-ionic regulatory mechanism experiments.