Effects of salinity on growth, molt and energy utilization of juvenile swimming crab Portunus trituberculatus

Abstract

We evaluated the effects of salinity on the growth,molt,and energy utilization of juvenile Portunus trituberculatus.The crabs were held at five salinities(15,20,25,30,and 35) and cultured in rectangular aquari-ums.Each treatment group was quadruplicated,with each replicate consisting of 3 stages(7 juveniles/stage).During the 50-day experiment,mortalities and incidence of "molt death syndrome" were recorded daily,while the intermolt period,carapace length,carapace width,and wet weight were measured at each molt.Salinity had a sig-nificant effect on growth and energy utilization.At salinities of 20,25,and 30,food intake(FId) was lower and food conversion efficiency(FCEd) was higher than in the control.At 30,FCEd was significantly higher than in crabs held at 15 and 35,but not different from those held at 20 and 25.The assimilation efficiency(K1) and net growth efficiency(K2) of crabs held at 20,25,and 30 were significantly higher than in the remaining groups.At the end of the experiment,crabs held at 25 and 30 had a higher wet body weight,relative body weight gain,and SGR.The difference was significant when compared to crabs held at 15 and 35 ppt,but not 20 and 25 ppt.Re-gression analysis suggested that maximum SGRd would occur at salinity 26.3.The molt recycle(MC) between instars VII–X ranged from 18.9 to 23.5 d,and was not different among the groups.Nevertheless,MC was 3.1-4.6 d shorter in crabs held at 30 than the remaining groups.MDS was observed at 15,suggesting that the lower salin-ity plays a role in inhabiting the molt of P.Trituberculatus.Conversely,new shell hardening was inhibited by higher salinity.Our results indicate that the culture water should be maintained at about 25 salinity to improve growth and molt success.