| Portunus trituberculatus is aggressive in nature and the phenomenon of cannibalism is extremely serious,resulting in its extremely low yield.And the installation of shelter is considered to be an effective way to prevent P.trituberculatus from cannibalism.This study will investigate the shelter habits of P.trituberculatus with different body weight,mating behaviors of P.trituberculatus and effects of shelter on the survival and growth of the polyculture species(Penaeus japonicus)of P.trituberculatus under the presence of shelter,so as to enrich the theoretical knowledge of behavioral ecology and reproductive biology of P.trituberculatus,and provide the scientific basis for further elucidating the mechanism of shelter in the cultivation and production of P.trituberculatus and optimizing the application technology of shelter in the cultivation and production.Based on our previous research,this study took the specially designed and customized plastic basket as the anti-injury shelter to explore the hidden behavior and molting growth of P.trituberculatus with different body weight(Group A: 5.80 ± 0.10 g,Group B: 12.10 ±0.25 g,Group C: 24.88 ± 0.08 g,Group D: 49.50 ± 1.27 g,Group E: 94.55 ± 1.27 g)under the presence of shelter.The results showed that: P.trituberculatus with different body weight had a higher occupancy rate of shelter in the daytime,and the occupancy rate of shelter increased with the increased body weight,among which the occupancy rate of shelter was as high as 71.52% in Group E.Under the conditions of the presence of shelter,P.trituberculatus with smaller body weight(Groups A,B,and C)had poor territorial awareness,and there were multiple individuals occupied the same shelter at the same time,while P.trituberculatus with the weight of 50 g or more(Group D,E)had strong territorial awareness,and most of them occupied one shelter alone.For molting,more individuals in each group chose to molt in the shelter,and the rate of molting in the shelter of Group B was as high as 81.15%,and that in the other groups was approximately 60%.Although the existence of shelter had no significant effect on the molting interphase and growth of P.trituberculatus(P > 0.05),the body weight,carapace width,weight growth rate and carapace width growth rate of each group of P.trituberculatus were slightly increased after molting.The existence of shelter could improve the survival rate of P.trituberculatus in each group,and the effect of shelter was relatively more obvious in individuals with large body weight,among them,the survival rate of P.trituberculatus was significantly improved in Group D(P < 0.05).In this study,the mating behavior of P.trituberculatus under indoor conditions and the role of shelters in its mating process were systematically studied by using behavioral observation methods.The results showed that the mating behavior of P.trituberculatus mainly includes pre-copulatory guarding,reproductive moulting,copulation,and post-copulatory guarding.P.trituberculatus in the no shelter group(NSG)usually preferred to gather at the edges or corners of the cement tank,while P.trituberculatus in the shelter group(SG)preferred to hide in the shelters.During the whole experiment,the shelter occupancy rate of P.trituberculatus during the day(57.40%)was significantly higher than that at night(38.08%)(P < 0.05).In terms of hiding rate,the hiding rate was as high as 63.32% during the day,which was significantly higher than that at night(37.70%)(P < 0.05).The copulation time of the SG was similar to that of the NSG.However,the duration of the pre-copulatory guarding period and post-copulatory guarding period of the SG were shorter than those of the NSG,indicating that the presence of shelters could shorten the total mating time of P.trituberculatus.The mating rates of NSG and SG were100% and 97.22%,respectively,with no significant difference between the two groups(P >0.05),showing that the presence of shelter did not prevent the occurrence of mating behavior.In addition,in this study,it was found that there was certain cannibalism during the reproductive moulting of female crabs,which could lead to the death or injury of some individuals.However,the survival rate of the SG(89.58%)was significantly higher than that of the NSG(72.92%)(P < 0.05).Moreover,the injury rate in the SG was only 14.13%,which was significantly lower than that in the NSG(31.31%)(P < 0.05).In general,shelters have obvious protective effect on P.trituberculatus during mating,shortening the total mating time,and can effectively reduce the incidence of intraspecific cannibalism during mating and improve the survival rate of P.trituberculatus.This study continued to investigate the effect of P.trituberculatus shelter on the hidden behavior and molting growth of polyculture P.japonicas based on the above study.The study showed that,in addition to P.trituberculatus,P.japonicas also had hidden behavior,but the hidden awareness of P.japonicas was poor,and its daytime hidden rate was only approximately 37%,which was significantly lower than that of P.trituberculatus(69.76%)(P < 0.05).In addition to intraspecific cannibalism,P.japonicas was subjected to predation by P.trituberculatus during the polyculture process,resulting in a low survival rate of less than 25%.Although the presence of shelter improved the survival rate of P.trituberculatus(NSG: 58.33%;SG: 72.22%),the presence of shelter had no significant protective effect on P.japonicas(NSG: 21.30%;SG: 23.15%).In addition,although there was no statistically significant difference in body weight,carapace width/body length,body weight growth rate,carapace width/body length growth rate,body weight specific growth rate,and carapace width/body length specific growth rate of P.trituberculatus and P.japonicus after molting between the SG and the NSG(P > 0.05),these growth indicators were slightly higher in the SG than that in the NSG. |
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