Study On Biology And Population Dynamics Of Macrobrachium Nipponense In Liangzi Lake

In recent years,with the deterioration of the water quality of Liangzi Lake,it has had a certain impact on the biological community inhabiting it.Macrobrachium nipponense is widely distributed in Liangzi Lake and occupies an important position in the ecosystem of Liangzi Lake.The study aims to find out the growth pattern of M.nipponense population in Liangzi Lake,and thus provide a scientific basis for its resource protection and the analysis of the ecological system of Liangzi Lake.From November 2020 to October 2021,M.nipponense were collected using ground cage at10 sampling points of Qianjiang Dahu and Dongliangzi Lake in the Liangzi Lake.And the collected 45160 M.nipponense samples were used to analyze and study their growth characteristics,reproductive characteristics,temporal and spatial distribution.The mian results are as follow:（1）The growth characteristics of M.nipponense in Liangzi Lake.There is no significant difference in the distribution of body length between male and female M.nipponense,and the population composition is complex;The relationship between body length and body weight of male and female are positive allometric growth,male:W=1.01636×10^-5L^3.1955;female:W=9.7350×10^-6L^3.2028.Taking May as the starting point of a new generation,the Von Bertalanffy growth equation of M.nipponense between 2and 10 months of age was fitted as:male:L_t（mm）=44.56^{[1-e-0.28（t+0.5213）]},W_t（g）=1.889[1-e^{-0.28（t+0.5213）}]^3.1955;female:L_t（mm）=32.30[1-e^{-0.58（t+0.4841）}],W_t（g）=0.664^{[1-e-0.58（t+0.4841）]3.2028}.The growth inflection point of male was estimated to be 3.4months,corresponding to body length and body weight of 29.70 mm and 0.52 g.There was no growth inflection point for female,and the growth rate continued to slow down after 2 months of age.（2）The reproductive characteristics of M.nipponense in Liangzi Lake.The species of M.nipponense in Liangzi Lake were divided into spring-summer population and autumn population.The annual sex ratio ranged from 0.2 to 0.87,and the sex ratio（♀/♂）in the breeding period was smaller than that in the non-breeding period.The breeding season is obviously divided into two stages,which are April to June in spring and summer and July to September in autumn.The breeding populations in spring and summer were mainly medium-sized and large-sized overwintering prawns,and the breeding populations in autumn were mainly small-sized current-year prawns.The absolute fecundity of female shrimp of spring-summer population is significantly higher than that of female shrimp of autumn population.The relationship between the number of eggs（F）and body length（L）and body weight（W）is:spring-summer population:F=0.036L^2.8038,F=858.32W+88.564;autumn population:F=0.0659L^2.594,F=820.07W+66.645.The relative fecundity R_L increased with the increase of body length,and the R_W did not change much with the increase of body weight.Both R_L and R_W of spring-summer population were significantly higher than those of autumn population.The volume of mature eggs ranged from 0.0472 to 0.1269 mm³,with the mean value is 0.0850±0.0142 mm³.The results show that although the population of M.nipponense in Liangzi Lake is in a relatively stable state,the breeding population tends to be miniaturized,and the fecundity is at a low level.（3）The temporal and spatial distribution characteristics of M.nipponense population in Liangzi Lake.In terms of spatial,the annual average of CUPE in Qianjiang Dahu was 30.06 tail/d,and the annual average CUPE in Dongliangzi Lake is44.82 tail/d.The total annual distribution of M.nipponense in Dongliangzi Lake is significantly larger than that in Qianjiang Dahu.Among the 10 sampling sections,the total annual distribution of M.nipponense was the largest in S6 and the smallest in S4;In terms of time,the annual change of the total distribution of M.nipponense in the whole lake is increase first and then decrease.It was at a low level from March to April,began to grow rapidly in early-May,reached a maximum in mid-June,then gradually decreased,and stabilized after November.Comprehensive analysis showed that the spatio-temporal distribution characteristics of M.nipponense were mainly determined by the reproductive characteristics of the population,the ecological environment characteristics and hydrological conditions of Liangzi Lake.