Effect of food ration on estrogen and vitellogenin plasma levels, fecundity and larval survival in captive sea bass, Dicentrarchus labrax: preliminary observations

Abstract

Adult two-year-old broodstock sea bass (Dicentrarchus labrax), raised in captivity, were fed ad libitum a natural diet (trash fish) until the end of their first spawning, and maintained under natural conditions of light and temperature. Six months before the second spawning, fish were randomly separated in two tanks with running sea water (salinity 37.80‰, pH 8.3) and maintained under similar environmental conditions. Fish were fed two different ration levels: group F, 1.04%, and group H, 0.45% body weight/day. The Jow ration supplied affected broodstock growth as indicated by decreased growth rates in weight and condition factor in group H, when compared to group F. The mean fecundity per female (No. eggs/female) in group H fish was similar to that from F group, while the relative fecundity (No. eggs/kg female) was more elevated in the H group. However, group H showed a delay in spawning time and slightly higher number of spawnings per female and larger spawning period, when compared to group F fish. In addition, group H females had reduced 17β-estradiol (E2) plasma levels and presented vitellogenic oocytes in the ovary a month later than group F females. By contrast, the vitellogenin (VGT) plasma levels remained similar between groups over the reproductive cycle. The egg quality (i.e. percentage of buoyant eggs), the egg biochemical composition and larval survival at hatching were similar between the two groups. The larvae from both groups also exhibited the same survival after 40 days of culture, although group H produced smaller eggs that yielded smaller newly-hatched larvae. Although the low ration supplied significantly reduced the growth and E2 plasma levels of sea bass, these preliminary results suggest that these changes do not dramatically affect the egg viability or the survival of larvae 46 days after hatching.