A 2-week research was carried out to
assess water salinity (WS) effects including 0, 15,
35, and 50‰ on osmoregulatory mechanisms and
stress indices in Asian sea bass (34.4 g) juveniles.
Except for fish reared at 50‰, in the other treatments,
it gradually decreased to the prescribed WS
during a 10-day period (− 5‰ a day). After a 10-day
acclimation period, fish were reared at the prescribed WS for 2 weeks. Fish reared at 15 and 35‰ had
higher chloride cell (CC) counts in the interlamellar
region. The number of CC in the interlamellar
region elevated with increment of WS up to 35‰,
but they were pronouncedly reduced in 50‰ group.
The diameter of CC in the interlamellar region was
not affected by WS. The smallest nucleus diameter
of CC in the interlamellar region was observed in
fish reared at 15‰ (P < 0.05). The largest and the
smallest amounts of serum aspartate aminotransferase
were observed in fish reared at freshwater and
15‰, respectively. Fish reared at 35‰ had the highest
serum sodium and potassium contents. Serum
chloride content and total osmolality increased with
increment of WS (P < 0.05). Serum cortisol and
glucose contents gradually increased with elevation
of WS up to 35‰; then, their contents remarkably
decreased. The relative expression of insulin like
growth factor-1 in the liver of fish reared at 35‰
was strikingly higher than that in the other groups.
The relative expression of HSP70 gene in fresh water
group was pronouncedly elevated compared to other
treatments. The relative expression of interleukin-1β
in 15 and 35‰ groups was higher than that in the
other groups; however, the relative expression of
lysozyme gene in the liver of fish reared at fresh
water was pronouncedly lower than that in the other
treatments. The results of this study suggested rearing
L. calcarifer at 15‰ closer to the isosmotic point
and better provide its welfare.