Study On The Fighting Behavior Of Chinese Mitten Crab (Eriocheir Sinensis) And Procambarus Clarkii Under Different Polyculture Conditions

Ecological polyculture mode,as an environment-friendly breeding mode,which can enhance the efficiency of aquaculture by increasing the effective utilization rate of water bodies.It will be the direction of aquaculture development in the future.Chinese mitten crab and crayfish are two important economic aquatic products in China,the development of the two ecological polyculture can not only make full use of the bait resources,but also promote the transformation from traditional culture model to modern culture model.However,in actual production,the attacking and fighting behavior caused by problems such as breeding density,stocking size,sex ratio and other issues greatly reduce the survival rate of crayfish and crabs,and the attack and defense lead to an increase in physical energy consumption and thus affect their growth.At present,the research focus on polyculture of crayfish and crab in China is mainly on economic benefits,and there are few reports on the behavior of their polyculture.In this study,the fighting behaviors of Chinese mitten crab and crayfish under different polyculture conditions were explored by setting different polyculture sizes and densities,and the key factors affecting the attack and fighting behaviors of crayfish and crab were preliminarily identified by indoor behavioral experiments,which provided some theoretical guidance for actual production.The results are as follows:1.Effects of different polyculture size on fighting behavior between Eriocheir sinensis and Procambarus clarkiiIn this experiment,two kinds of crayfish and crab polyculture methods of the same size and different size were set up,and the approach,contact,alert,attack and fighting behavior of the two were statistically analyzed under four conditions,such as initial encounter during the day,encounter at night,hunger and re-feeding.The results showed that under the condition of equal size,the attack and fighting behaviors of 25 g crayfish and crab were higher than those of 10 g crayfish and crab,but there was no significant difference(P > 0.05).Larger crayfish and crab were more likely to deter each other than smaller crayfish and crab,and the difference in deterrence behavior during the initial encounter during the day and in the state of starvation is significant(P < 0.05),while others were not.However,smaller crayfish and crab were more likely to approach and touch,but this difference is not significant.In addition,when the size of crayfish was the same,the larger the size of the crab,the more times they attacked and fought,and the number of fights between 10 g crayfish and 10 g crab was significantly higher than that of 10 g crayfish and 5 g crab during the initial encounter of the day and the night(P< 0.05),and there was no significant difference among other groups.When the size of the crab was the same,the variation of crayfish’s size,which has no significant effect on the attack,fighting and other behaviors between them.The fighting times of each size group at the initial encounters in daytime were higher than those at night,but the difference was not significant.When crayfish and crab which starved for 48 hours were re-fed with compound feed,the fighting times of polyculture crayfish and crab in each group were fewer than those starved for 48 hours,but there was also no significant difference.To sum up,under the condition of polyculture,the change of light was not the key factor that causes the change of shrimp and crab behavior.In addition,with the increase of crab specifications,the number of fights and the risk of killing each other between crayfish and crab may increase.2.Effects of different polyculture densities on the fighting behavior between Eriocheir sinensis and Procambarus clarkiiIn this experiment,on the basis of the size experiment,the Chinese mitten crab and crayfish with specifications of about 12 g were selected for polyculture experiment according to the densities of 1:1,1:2,1:4 and 1:8,and the control group was crab kept alone.Fighting behaviors of each group were statistically analyzed,and the lactic acid content of hemolymph and cheliped muscle of crabs was measured.The results showed that with the increase of the density of crayfish,the times of contact,alerting and attack between crayfish and crab showed an increasing trend.Moreover,the times of contact,vigilant and assault at the density 1:8 group were significantly higher than other four groups(P < 0.05),while the number of approaching and fighting first increased and then decreased with the increase of density.Both hemolymph and cheliped muscle lactic acid levels were consistent with the trends of fighting behavior.Males fight more than females at all polyculture densities.In addition,when the shooting was divided into two stages of 30 minutes,it was found that each group had a higher number of fights in the first 30 minutes than in the last 30 minutes.In summary,in the polyculture of Chinese mitten crab and crayfish,the fighting behavior between crayfish and crab may decrease with the initial establishment of the social hierarchy of crayfish.Moreover,appropriate sex ratios and appropriate increase of crayfish density can alleviate the pressure of crayfish and crab fighting,but whether it is feasible in actual production still needs further study.3.Food source analysis of Eriocheir sinensis and Procambarus clarkii under different polyculture densitiesIn this experiment,the same specifications and density condition as the indoor density experiment were set,and mixed culture of Chinese mitten crab and crayfish was carried out in outdoor ponds for 60 days.At the end of the polyculture,samples of Chinese mitten crab were collected to measure their growth performance and conventional biochemical composition,and the food sources of crab and crayfish under mixed culture were analyzed by using stable isotope technology.The results showed that as the density of crayfish increased,the male and female crabs’ survival rate first decreased but then increased.The muscle yield of male crabs at the group of 1:4 was significantly higher than muscle yield of the control group and density 1:1 group,while there was no significant difference in muscle yield among female crabs,and all of them were lower than that of male crabs.Under the condition of polyculture,the top three recipes of Chinese mitten crab and crayfish were compound feed,snails and Elodea nuttallii.However,with the increase of polyculture density,the contribution rate of feed to Chinese mitten crab showed a trend of first decreasing and then increasing.When the density was 1:4,the contribution rate of feed was the lowest,while the contribution rate of crayfish to Chinese mitten crab increased significantly compared with that of 1:2.