Effects Of Shelters On Molting,Survival,Growth And Culture Performance Of Portunus Trituberculatus

The study is designed to select the shelter that prevents cannibalism of Portunus trituberculatus,and on this basis,we study the effects of shelter on molting,survival,growth and culture performance of P.trituberculatus,together with an analysis of the economic-benefit involved.The primary results of these studies are listed below.1.Effects of different shelters on the molting and growth of P.trituberculatus in laboratory.In this study,we select two types of materials(polyethylene net and plastic basket)as potential shelters to evaluate their differences on the molting and growth of swimming crab with body weight of 25.15±0.22 g in laboratory conditions.Shelter 1(S1)was made into Z-like shape by polyethylene nets while shelter 2(S2)was made by a half plastic basket.The results showed that 15% of the swimming crabs preferred to complete the molting in the shelter of S1,while 45% tended to complete the molting in the shelter of S2.Compared with S1,crabs in S2 showed a significantly higher hiding rate and molting rate(P < 0.05).In particular,shelter 2 can effectively shorten the molting period and improve both the weight growth rate and the specific growth rate of crabs after molting.Moreover,S2 can well prevent the cannibalism because crabs in this group performed a significantly higher survival rate and lower disabled rate than those both in the S1 group and in the control group(P < 0.05).2.Study on the hiding and mating behaviors of P.trituberculatus with different sizes in laboratory.Previous research results showed that S2 can well prevent the cannibalism,on this basis we had to change the size of the shelter and set up six groups of swimming crabs with sizes of 3.2±0.5g,9.4±1.0g,30.7±2.2g,50.3±2.8g,90.4±3.4g,170.6±5.5g,researched the differences of hiding with different sizes of swimming crabs and the female crabs(170.8±15.3g)mating behaviors under the shelter condition(after the transformation of the shelter,the same as below).The main results showed that: There were significant differences in the hiding and mating behaviors of different sizes of swimming crabs.The hiding rate of small-sized swimming crabs was significantly lower than that of large-sized(P<0.05).Small-sized swimming crabs exhibited obvious constellation effect(multiple individuals occupy the same shelter)and had poor territory and hidden consciousness,most of the large-sized swimming crabs were independent and had a strong sence of territory.In addition,during the mating period,56.7% of the female swimming crabs chose to complete the reproductive molting in the shelter,while 43.3% of the female swimming crabs chose to carry out the molting activity outside the shelter,the difference between the two groups was significant(P<0.05).Meanwhile,there was a significant difference between 63.3% of the female swimming crabs that completed the molting chose to complete the mating activities in the shelter and 36.7% of the female swimming crabs chose to complete the mating outside the shelter.3.Effects of different numbers of shelters on survival,growth and hidden behavior of swimming crabs in laboratory.In this experiment,four quantitative gradient groups of shelters were set(group A: 40pcs;Group B: 30pcs;Group C: 20pcs;Group D: 10pcs)in laboratory culture pond.The purpose was to evaluate the effects of difference numbers of shelter on growth,molting,survival and hidden behavior of swimming crabs.The main results showed that the survival rate of swimming crabs in group A was as high as 73.3%,while that in group D was only 41.7%,the difference between the two groups was significant(P<0.05).The weight gain rate of each group was significantly different(P>0.05)and the weight gain rate of group A was the highest,Meanwhile,the specific growth rate of swimming crab in group A was significantly higher than that in group D,but there was no significant difference between group B and group C(P > 0.05).Finally,the number of the shelters had no significant effect on the molting cycle of the swimming crabs.4.Effects of different numbers of shelters on the culture performance and economic-benefit of swimming crabs under the condition of outdoor cultured pond.Set up four quantitative gradient groups of shelters in outdoor culture ponds(Group A: 300pcs/mu;Group B: 420pcs/mu;Group C: 540pcs/mu;Group D: 660pcs/mu)to study the effects of different numbers of shelters on the culture performance and benefit of swimming crab to further verify actual breeding efficiency of the shelter developed in laboratory.The results showed that the amount of the shelters had no significant effect on the weight gain rate and specific growth rate of swimming crabs in outdoor culture pond(P>0.05),but the survival rate and yield of group D significantly higher than that of group A,group B and group C(P<0.05),the survival rate and yield of group A was the lowest,however,there was no significant difference between group B and group C(P>0.05).In addition,the feed coefficient showed an obvious decreasing trend,the feed coefficient was the highest in group A,the lowest in group D,there were differences between the two groups(P<0.05),but there was no significant difference between group B and group C(P>0.05).It was proved that the shelter developed in laboratory had good function of preventing cannibalism,the more of shelters the higher of the survival rate and yield of swimming crabs.