| The growth of any organism needs an appropriate temperature.As a breeding object with high economic benefits,the scale of Chinese moped crab(Eriocheir sinensis)is increasing day by day,and temperature as one of the most important factors affecting its growth and molting plays a crucial role in the breeding process.However,the optimal temperature for the molting growth of Chinese mitten crab has not been accurately studied.In this paper,the optimal molting temperature of Chinese mitten crab was accurately analyzed by using the individual culture system with constant temperature,and the influence of temperature about the gut microbiome of Chinese mitten crab was discussed,which provided an important reference for the culture and production practice.The main results were presented as follows:1.Effects of water temperatures on molting,growth and feeding rate of Chinese mitten crabIn order to investigate the effects of different water temperatures on the molting,growth and feeding rate of juvenile Chinese mitten crab(Eriocheir sinensis),the survival rate,molting number and interval,weight gain rate,condition factor and feeding rate were analyzed by using the constant-temperature individual culturing system of crabs under different water temperatures.The results show that: during the 133-day experiment,the survival rate of Chinese mitten crab under different water temperatures was more than89 %;the experimental crabs only molted one time at the water temperature of 10 ℃ and15 ℃,two times at 20 ℃ and 25 ℃ three times at 30 ℃;the average molting interval of the five water temperature groups were 109.39 d,67.92 d,46.63 d,43.69 d and 38.01 d,respectively.The weight gain rate increased gradually with the increase of water temperature,and the weight gain rate in 30 ℃ was significantly higher than that in other water temperatures(P < 0.05).The average absolute growth rate and relative growth rate increased gradually with the increase of water temperature,and there were significant differences among the water temperature groups(P < 0.05).However,the condition factor decreased with the increase of water temperatures.The average feeding rate of the five water temperature groups from 10 ℃ to 30 ℃ was 1.58 %,1.97 %,3.54 %,4.79 % and5.25 %,respectively.Microscope observation of leg muscle sections showed that the diameter of muscle fibers in the low water temperature groups(10 ℃,15 ℃,20 ℃)was significantly larger than that in the high water temperature groups(25 ℃,30 ℃)(P <0.05).This study shows that the molting speed of crabs was accelerated,the weight gain rate would increase,the condition factor would decrease,and the feeding rate of crabs would increase when water temperature was increased.This study indicated that the better water temperature should be 30 ℃ for molting and growth in juvenile Chinese mitten crab.2.Effects of water temperatures on growth and enzyme activity of Chinese mitten crabIn order to verify the optimal growth temperature of crabs,this chapter further refined the temperature gradient based on the results of the last chapter.Four different water temperatures(26 ℃,29 ℃,32 ℃,35 ℃)were set for 121 days rearing,and the effects of different water temperatures on the growth,molting,feeding rate and digestive enzyme activity were analyzed.The results showed that the water temperature group at 26 ℃,29 ℃ and 32 ℃ molted twice,while the water temperature group at 35 ℃ molted only once.The survival rate of crabs in the 26 ℃,29 ℃ and 32 ℃ water temperature groups was more than 80 %,while the survival rate of crabs in the 35 ℃ water temperature group was just only 25 %.The molting interval in 26 ℃ water temperature group was significantly higher than that in the other three water temperature groups(P < 0.05).With the increase of water temperature,the weight gain rate of molting decreased first and then increased,and the weight gain rate of molting in 29 ℃ and 32 ℃ groups was significantly higher than that in 26 ℃ and 35 ℃ groups(P < 0.05).With the increase of water temperature,the absolute growth rate and relative growth rate also increased at first and then decreased,and the growth rate of 29 ℃ and 32 ℃ water temperature groups was significantly higher than that of 26 ℃ and 35 ℃ water temperature groups(P < 0.05).There was no significant difference in the condition factor of crabs among four water temperature groups(P > 0.05).With the increase of water temperature,the feeding rate of crabs was also increased,the feeding rate of 32 ℃ and 35 ℃ water temperature groups was significantly higher than that of 26 ℃ and 29 ℃ water temperature groups(P < 0.05),and the feeding rate of 29 ℃ water temperature group was significantly higher than that of 26 ℃ water temperature groups(P < 0.05).The activities of digestive enzymes also showed a similar trend,that with the increase of water temperature,they increased first and then decreased.The activities of enzymes were higher in the water temperature groups of 29 ℃ and 32 ℃.The results showed that the higher the temperature in a certain temperature range,the better the crab growth.3.Effects of temperatures on gut microbiota of Chinese mitten crabTo explore the relationship between gut microbiota and growth of Chinese mitten crab(Eriocheir sinensis)under different water temperatures,16 S r RNA high-throughput sequencing was used to analyze the growth performance and gut microbiota composition of this crab under four kinds of water temperatures(26 ℃,29 ℃,32 ℃,and 35 ℃)in this study.The sequencing results of the gut microbiota showed that 929,744,680 and518 Operational Taxonomic Units(OTU)were obtained for the 26 ℃,29 ℃,32 ℃ and35 ℃ water temperature groups,respectively.The Ace,Chao and Shannon indexes showed a decrease,but increase of Simpson index with the increase of water temperature.The results of β diversity(ANOSIM)analysis showed that there were significant differences(P < 0.05)for the gut microbiota composition among the four water temperature groups.At the phylum level,the dominant gut microbiota for the four water temperature groups were Firmicutes,Bacteroidota and Proteobacteria,which accounted for 96.26 % of the total microbiota.The abundance of Chloroflexi,Patescibacteria and Verrucomicrobia in the 26 ℃ was significantly higher than that in the other water temperature groups(P < 0.05),the abundance of Firmicutes and Actinobacteriota in the29 ℃ was significantly higher than that in the other water temperature groups(P < 0.05),and the abundance of Bacteroidota in the 32 ℃ was significantly higher than that in other water temperature groups(P < 0.05).At the genus level,the abundance of Gemmobacter in the 26 ℃ was significantly higher than that in the other water temperature groups(P <0.05),the abundance of Genus Candidatus-Hepatoplasma in the 29 ℃ was significantly higher than that in the other water temperature groups(P < 0.05),the abundance of Pragia in the 32 ℃ was significantly higher than that in other water temperature groups(P <0.05),and the abundance of Psuedomonas in the 35 ℃ was significantly higher than that in other water temperature groups(P < 0.05).The results of this study indicated that: the best water temperature should be 30 ℃ for growth of Chinese mitten crab and its growth would be inhibited when temperature is over 32 ℃.The diversity and abundance of gut microbiota would decreased with the increase of water temperature,the appropriate bacterial population ratio is conducive to the molting and growth of Chinese mitten crab.Under high temperature condition,some harmful flora,such as Campilobacterota and Malaciobacter,would be dominated and affect the molting and growth of Chinese mitten crabs. |
