| Aquaculture is one of the sectors in the world that is contributing to world food production by increasing significantly over the years nearly half of the total supplies of fish,shellfish,crustaceans,and many aquatic species consumed by humans today.In the year 2018,the total output of aquaculture in China exceeded 50 million tons,accounting for more than 78%of the total output of aquatic products in China.It is the only major fishery country in the world where the total amount of aquaculture products exceeded the total amount of capture fisheries.However,Fish growth,feed utilization,and the gross fish yield are affected by stocking densities as one of the most important factors in fish farming practices.Also,fish reproductive behavior Studies are significant and a basic requirement for improvement and effective fishery resources management and conservation.This study investigates the stocking density and reproduction characteristics of GIFT strain Nile tilapia.The research was conducted at an experimental location Shangdou East Road,Qiting,Yixing City,Tilapia Genetic Breeding Center of China.To investigate the reproduction characteristics of GIFT strain Nile tilapia,two hundred and forty hapas were set in concrete ponds in the greenhouse with the same conditions,the water temperature was about 28℃ the same for all.The fish were given feed once a day.The breeders with higher breeding value to the lower breeding value were listed and divided into three groups were group1 from number 1 to 34 as higher,group2 from number 35 to 68 as a medium,and group3 from number 69 to 102 as lower respectively.The body weight,fecundity and hatching rate of female breeder parents were compared and analyzed.In order to study the effect of stocking density on growth,the body weight gain,yield per unit area,body weight and body length,body size and feed conversion ratio were analyzed.The results were as follows.(1)The Experiment of reproduction comparing with different breeding values①the weight of breeding parents and their genetic breeding values.The average bodyweight of Group 2 has the highest breeding value of 549.24±253.37g,Group 1 with minimum breeding value of 517.50±197.37g,and Group 3 with the lowest breeding value of 506.56±178.20g respectively.There was no difference in the analysis of variance of weight between Group 1-group2 and Group 1-Group 3(P>0.05),while there was difference between Group2-and Group 3(P<0.05)②Genetic breeding value and fecundity.The absolute fecundity of Group2(1755.21±830.53)was higher than that of Group1(1715.21 ±819.26)and Group3(1510.03±7285.59),the variance test showed no significant difference among the three groups(P>0.05).The relative fecundity of Group1(3.21 ±2.18)was higher than that of Group2(3.08±2.28)and Group3(2.94±2.39).The variance test showed no significant difference among the three groups(P>0.05),and there was no correlation difference between genetic breeding value and absolute fecundity and relative fecundity.③ Genetic breeding value and hatchability.Group1 had the highest hatching rate(0.4616±0.1339),followed by Group2(0.300±10.1661),and Group3 had the lowest hatching rate(0.2435±0.1149).According to variance analysis,there were significant differences among the three groups(P<0.05),and there was a significant correlation between the hatching rate and the genetic breeding value of the population.(2)The effect of parental weight and fecundity①Correlation analysis of maternal weight and fecundity.In the correlation analysis between body weight and absolute fecundity,the P-value was 5.529E-4(P<0.05),and the P-value of relative fecundity was 0.001871(P<0.05).The results showed that both absolute fecundity and relative fecundity were significantly related to maternal body weight.②Correlation analysis between maternal weight and hatchability.The P-value of correlation between maternal weight and hatchability was 0.2094(P>0.05),which indicated that the hatchability was not correlated with maternal weight.(3)Regression analysis of maternal body weight and fecundity.The regression analysis of maternal weight and absolute fecundity,the regression coefficient R-squared is 0.5040,which is higher than that of maternal weight and relative fecundity(R-squared=0.1588).The results showed that maternal body weight was correlated with relative fecundity and absolute fecundity,but it was more correlated with absolute fecundity.(4)The effect of stocking density on growthIn order to study the effect of stocking density on the growth of tilapia species,360 species of GIFT tilapia were stock-fed in hapa-nets in concrete ponds at four treatment densities of 15,25,35 and 45 fish/m3,with each treatment repeated three times.In order to evaluate the growth performance of the fish,the fish were fed with the daily feeding amount of 5%of body weight at 40%,40%and 20%of the diet three times a day(8 AM,12 PM and 5 PM).The total weight of each treatment and replicate was measured before feeding,and the weight was weighed every 10 days for a consecutive month.In the final stage,the individual’s weight and body length were also measured and recorded.During the period,the water temperature was 28.5±2.1(mean ± 2SD)℃,the dissolved oxygen was 6.2±2.5(mean± 2SD)mg/L,the water depth of the hapas were 0.7 m,and the pH value was about 7.5-8.① Body weight and body length growth.The average body weight and body length of 15 fish/m3 were the largest(33.45±7.78g and 95.2±6.16mm),while the average body weight and body length of 45 fish/m3 were the smallest(27.25±5.64g and 88.59±5.70mm),with significant differences among all levels(P<0.05).There were significant differences in body length between 15,25 and 35 fish/m3 levels(P<0.05),and no significant differences between 35 and 45 fish/m3 levels(P>0.05).The relationship between body weight and body length was a power function,and it was not affected by stocking density.② Output per unit area.With the increase of stocking density,the fish size decreases gradually but at the same time the yield increases gradually.The output per unit area of 15 fish/m3,25 fish/m3,35 fish/m3 and 45 fish/m3 were 501.75,775,988.4 and 1226.25 grams,respectively.③ Feed coefficient and survival rate.Variance analysis of feed conversion ratio and survival rate among all treatments showed that P values were all less than 0.05,and there were no significant differences in feed conversion ratio and survival rate among all treatments(5)Coefficient of variation of individual growth.The analysis of body length variation coefficient,the 45 fish/m3 treatment was the smallest(6.43%),and the 35/m3 treatment was the largest(6.88%),and there was no significant difference in the variation coefficient among all treatments(P>0.05).In the analysis of coefficient of variation of body weight,45 fish/m3 treatment had the largest body weight(20.69%),and 35/m3 treatment had the smallest body weight(23.29%),and there was no significant difference among all treatments(P>0.05). |
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