盐度对三疣梭子蟹生长、蜕壳及能量利用的影响

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

在实验室条件下,研究了盐度（15,20,25,30,35）对三疣梭子蟹（Portunus trituberculatus）幼蟹生长、蜕壳和能量利用的影响,探讨了三疣梭子蟹生长的最适盐度、蜕壳与生长的关系以及不同盐度水平下蟹的蜕壳同步性。实验时间为50 d,结果显示：1、盐度显著影响三疣梭子蟹的摄食、生长和能量利用。盐度20、25和30组,三疣梭子蟹的日摄食率（FId）较小,但其食物转化效率（FCEd）较高,其中盐度30组蟹的食物转化效率显著高于盐度15和35组（P〈0.05）,与盐度20和25组差异不显著（P〉0.05）。盐度20、25和30组的能量吸收效率（K1）和净生长效率（K2）显著高于盐度15和35组。实验结束时,盐度30组三疣梭子蟹获得了较高的湿重、相对增重率和特定生长率,且显著高于盐度15和35组（P〈0.05）,而与盐度20和25组间的差异不明显（P〈0.05）。回归分析表明,当水体盐度为26.3时,三疣梭子蟹特定生长率（SGRd）最大。2、不同盐度下,三疣梭子蟹幼蟹从Ⅶ期生长到Ⅹ期的蜕壳周期为18.9~23.5 d,各盐度组间的差异不明显（P〉0.05）,但盐度30组三疣梭子蟹蜕壳周期较其他盐度组缩短了3.1~4.6d。低盐（15）下,三疣梭子蟹出现MDS（蜕壳未遂）死亡,蜕壳受到抑制;而高盐（35）则抑制三疣梭子蟹新壳的硬化,盐度20和25组三疣梭子蟹的蜕壳同步性较好。实验结果初步表明,养殖生产中水体盐度控制在25左右有利于三疣梭子蟹的蜕壳同步及生长。

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.