Effects of Salinity on Survival and Growth of Postlarval Penaeus vannamei

Eight and 22-day-old Penaeus vannamei postlarvae were exposed to several salinities for 24 hours and 120 hours by direct transfer from 32 ppt salinity to lower salinity waters. The challenge study included six experiments conducted on 8-day-old postlarvae (PL-8) and five experiments conducted on 22-day-old postlarvae (PL-22). Each experiment consisted of ten replicates of ten animals each. Shrimp were held in 1 L plastic containers with 500-ml of seawater. Lowered salinity resulted in lower survival for shrimp of both ages. Longer exposure time resulted in lower survival for shrimp of both ages. Younger shrimp exhibited lower survival than older shrimp. Survival of 8-day-old postlarvae after 24-hour exposure to salinities of 32, 16, 8, 4, and 2 ppt was 97.3%, 92.8%, 19.8%, 8.2% and 1.7%, respectlvely. Survival of 22-day-old postlarvae after 24-hour exposure was 99.2%, 97.8%, 83.8%, 63.4% and 40.2%, respectively. A second series of experiments investigated the effect of salinity upon growth of 22-day-old postlarvae which had been acclimated to four different salinities (16, 8, 4, and 2 ppt). Thirty shrimp were stocked in triplicate into 113 L (30 gal) aquaria and fed a prepared commercial feed. Growth was determined after 30 days at 16oC and 28-30oC. Growth was greatest at higher temperatures, but statistically significant differences due to salinity were not detectable. Nonetheless, best observed growth occurred at the intermediate salinities of 8 and 4 ppt.