Effects of salinity at the embryonic stage on salinity tolerance and digestive enzyme activities of striped catfish (Pangasianodon hypophthalmus) in the fry stage
Abstract
The aim of this study was to evaluate the effects of salinity exposure during the embryonic development stage on the salinity tolerance of striped catfish (Pangasianodon hypophthalmus) at the fry stage. The experiment was designed with 2 factors (salinity level at incubation and nursery stage), including 12 treatments and 4 repetitions. After fertilization, eggs were incubated at different salinities 0‰, 1‰, and 2‰, after hatching, larva were nursed at different salinities 0‰, 4‰, 8‰ and 12‰. The results showed that after 35 days of nursing, the salinity level of incubation and nursery did not show to have an effect on the larval growth, but affected on the survival rate, osmolality, and activity of some digestive enzymes such as pepsin, trypsin, chymotrypsin and amylase. Salinity reduces the survival rate of nursed fish, but the group of fish incubated at high salinity (2‰) tends to tolerate salinity better than when reared at high salinity (12‰) (p<0.05). The osmolality of nursed fish increased as salinity increased, and the group of fish incubated at 2‰ salinity had the largest increase in osmolality while rearing at high salinity of 12‰ (p<0.05). The enzymatic activity of nursery fish tends to increase as salinity increases. This study shows that early exposure of fish to salinity can increase the salinity tolerance of fish at the fry stage.
