Preliminary Study On Breeding Strategy Of (Scomberomorus Niphonius) In Xiangshan Bay

Blue point mackerel(Scomberomorus niphonius)is one of the few important economic fish species with continuous high yield under the background of the decline of offshore fishery resources.The reproductive strategy of its spawning population is the key to the control of reproductive success,which determines the reproductive success rate,thus affecting the supplement of fishery resources of blue point mackerel.Research on reproduction strategy can better serve fishery resource management.Based on the research status of fish reproduction at home and abroad,this study summarized the biological characteristics,reproductive strategies and research methods of Marine fish,enriched the biological characteristics of blue mackerel in Xiangshan Bay of East China,and provided theoretical basis and important basis for population identification,life history research,resource development and rational utilization of blue mackerel in Xiangshan Bay of East China.It is suggested to continue to focus on the conservation policy of "Blue Point Horse mackerel National Aquatic Germplasm Resources Conservation Area",strengthen the breeding and release,ecological control,restoration and protection of Xiangshan Bay,and scientifically protect the breeding parents of blue point horse mackerel entering the spawning ground of Xiangshan Bay.In this paper,samples collected at Xiangshan Bay from March to May 2016 were first used as research objects,and biological characteristics such as fork length,body weight,sex ratio,sexual maturity,fork length at initial sexual maturity,feeding intensity and fatness were studied,aiming to further understand the growth rules and population characteristics of blue mackerel in breeding season.The results showed that the fork length range of Xiangshan Bay blue point horse mackerel was 400～1050mm,the average fork length was 634.32±142.09 mm,the dominant fork length group was450～699mm and 750～899mm,accounting for 84.43%.The univariate analysis of variance showed that,The fork length distribution of male and female populations of blue point mackerel was significantly different(P < 0.05).The weight range was900-7900 g,the average weight was 2352.74±1437.63 g,and the dominant weight group was 1000-2999 g,accounting for 76.35%.There were statistically significant differences in the weight distribution of male and female populations of blue point mackerel as a whole(P < 0.05).The b value of the fork length-body weight relationship was 2.0561,and the b value was less than 3,indicating that the blue point mackerel was in negative allometric growth,and the effect of sex on the fork length-body weight relationship was significant(P < 0.05).The ratio of male to female was 1:0.52,and the difference between male and female ratio and 1:1 was significant(P<0.05).The gonad maturity was mainlyⅤ stage,and there were four stages of gonad development,maturity,postoviposition and recovery stage.Multivariate variance analysis showed that there were significant differences between fork length and body weight on maturity(P < 0.05).The first fork length of sexual maturity(L50)was 486.34 mm.There were significant effects of fork length and body weight on feeding intensity(P < 0.05),and there was significant correlation with sex(P < 0.05).The fatness ranged from 0.41 to 2.73,with an average of 0.91.Female fatness was lower than male fatness.With the increase of fork length and body weight,the fatness of blue point horse mackerel decreased,and there was a significant correlation between the fatness and fork length and body weight groups(P<0.05).The generalized additive model based on Poisson distribution,the finite mixed model based on binomial distribution and the generalized linear model based on binomial distribution were used to analyze the changes of sex and body size and sex ratio of blue point mackerel.The results showed that in the early breeding stage in late March,when the sea temperature was relatively low(12-14.2 ℃),the population of blue mackerel from the East China Sea migrated to the waters of Xiangshan Bay one after another.The number of male mackerel entering Xiangshan Bay was higher than that of females,and the females were mainly large individuals.In mid to late April,the sea temperature gradually increased to the optimal temperature(14.2～19.4℃)of blue point mackerel.The number of female and male groups gathered in the spawning ground at the same time reached the peak,and the sex ratio was close to 1:1.In early May,the sea temperature continued to rise(19.6～21.5℃),and the number of males and large females decreased significantly,while the number of small females was relatively stable.In late May,only a small group of individual females remained.Analysis showed that males arrived at the spawning ground before females.In females,larger individuals arrive before smaller ones.This spawning and migratory rhythm is consistent with a reproductive strategy that maximizes generation replenishment and reproductive returns.According to the research,the spawning period of blue point mackerel in Xiangshan Bay is from late March to the end of May,and the peak spawning period is from mid to late April.Therefore,it is suggested that the fishing closure period in Xiangshan Bay Reserve should be from April 1 to May 31.