THE EFFECT OF SALINITY ON GROWTH AND SURVIVAL OF PENAEUS-VANNAMEI, WITH OBSERVATIONS ON THE INTERACTION OF IHHN VIRUS AND SALINITY

Penaeus vannamei juveniles (initial mean weight = 1.6 g) were cultured at salinities of 5, 15, 25, 35, and 49 ppt for 35 days. Highest mean final weights and greater than 2 g/week growth were obtained in the lowest salinities tested, 5 and 15 ppt. Mean final weights at 5 and 15 ppt were not significantly different, but were significantly greater than at the higher salinities tested. Mean final weights at 25 and 35 ppt were not significantly different, but were significantly greater than at 49 ppt. Mean final weights by treatment were: 12.4 g (5 ppt), 12.2 g (15 ppt), 10.8 g (25 ppt), 11.1 g (35 ppt), and 9.8 g (49 ppt). Survival was not significantly different among salinity treatments. A second population of juveniles (initial mean weight = 2.2 g), infected with IHHN virus (infectious hypodermal and hematopoietic necrosis virus), was compared concurrently at 25 and 49 ppt. The growth pattern was similar, with significantly higher mean final weights at 25 ppt than at 49 ppt. Additionally, a significant interaction between population and salinity level (two-way ANOVA, P = 0.035) indicated that the IHHN-positive population had relatively lower growth at the high salinity level. Mean final weights in the second population were 10.3 g (25 ppt) and 8.5 g (49 ppt). As in the population not infected with IHHN, survival was not significantly different among treatments.