Effects Of Different Feeding Frequency And Dietary DHA/EPA Ratio On The Reproductive Performance And Offspring Quality Of Litopenaeus Vannamei Broodstock

To study the feeding strategy and nutritional requirement of Litopenaeus vannamei broodstocks in their nutrient enrichment phase,we explore the effects of different feeding frequency and dietary DHA/EPA ratio on the reproductive performance and offspring quality of broodstock.The results showed that:1.Effects of different feeding frequency on the reproductive performance and offspring quality of Litopenaeus vannameiA study was conducted to investigate the effect of feeding frequency on growth,reproductive performance,body composition and digestive enzyme of broodstock Litopenaeus vannamei.Experimental broodstock were fed with Nereis succinea for30 days.Before the start of the experiment,the unilateral eye socket of each broodstock was placed on the eye as an individual marker and the initial body length and weight of each female were determined.The average initial body weight was41.78 g and the average initial body length was 15.80 cm.The broodstock were randomly divided into three round pools,each with 40 shrimp.Three groups of broodstock were fed to satiation in two times per day,three times per day and four times per day,which were represented by F2,F3 and F4 groups,respectively.Results showed that the feeding amount of broodstock increased gradually with the increase of feeding frequency,and the F2 group was significantly lower than that in group F4(P <0.05),but there was no significant difference between the F3 group and the F2 group(P>0.05).The weight gain and body length growth of broodstock increased first and then decreased with the increase of feeding frequency,but there was no significant differences among treatments(P>0.05).Reproductive performances of Litopenaeus vannameimei were not affected by different feeding frequency in currentstudy(P>0.05).There were no significant differences in single fecundity,relative fecundity,the number of nauplius stage I,hatching rate,the number of zoea stage metamorphosis rate(N1-Z1),gonadosomatic index(GSI),first spawning time and the spawning intervals(P>0.05).The body composition of Litopenaeus vannamei including water content,crude protein,crude fat and ash were not affected by feeding frequency(P>0.05).The results showed that the activity of trypsin and lipase of hepatopancreas in the F2 group was significantly lower than that in the F3 and F4groups(P<0.05),but there was no significant differences among the activity of pepsin and amylase in different experimental groups(P>0.05).Based on the results of this experiment and the actual production conditions,the optimum feeding frequency of nutrient fortification in Litopenaeus vannamei broodstock is suggested to be 2 times per day.2.Effects of dietary DHA/EPA ratio on the reproductive performance and offspring quality of Litopenaeus vannameiFour isonitrogenous and isolipidic experimental diets were formulated to contain different DHA/EPA levels:group DHA/EPA-0.47,group DHA/EPA-0.78,group DHA/EPA-1.34 and group DHA/EPA-2.07.Nature DHA/EPA-0.47,baits Nereis succinea as the control group were used in the experiment.The nutrient enrichment stage lasted for 75 days with the Litopenaeus vannamei of 4th months.After nutrient enrichment,the weight gain rate of the control group in female broodstocks was the highest,followed by the DHA/EPA-1.34 group.And the group significantly higher than that of the DHA/EPA-2.07 group(P<0.05);the weight gain rate of the male broodstocks had no significant differences(P > 0.05)between contrast group,but it was significantly higher than that of the other groups(P<0.05).The hepatopancreas index of the female DHA/EPA-1.34 group was the lowest,significantly lower than that of the DHA/EPA-2.07 group(P<0.05).However,there was no significant difference with the other groups(P>0.05).The hepatopancreas index of male broodstocks had no significant difference among the groups(P>0.05).As to GSI,there was no significant difference between DHA/EPA-1.34 group and contrast group(P>0.05),but there here was significant difference with the other groups(P<0.05).The content of estradiol inserum had no significant differences between contrast group,DHA/EPA-0.78 group and DHA/EPA-1.34group(P>0.05),but significant difference with the other two groups(P<0.05).The fecundity has no significant difference between the feed DHA/EPA-1.34 group and the control group(P>0.05),but it is significantly higher than that of the other groups(P<0.05);There was no significant difference in spawning rate between the control group and the feed DHA/EPA-0.78 group(P>0.05),but it was significantly higher than that in the other groups(P<0.05).However,continuous spawning rate of the feed DHA/EPA-0.78 group was the lowest,and it was significantly lower than that of the other groups(P<0.05).There was no significant difference in the average spawning times between the groups(P>0.05).The hatching rate of fertilized eggs in the DHA/EPA-0.47 group was the highest,and there was no significant difference with the control group(P>0.05).Compared with the other groups(P<0.05),the metamorphosis rate of the nauplius in the DHA/EPA-0.47 group was also the highest,which was significantly higher than that of the DHA/EPA-1.34 group and the DHA/EPA-2.07 group(P<0.05).There was no significant difference between the control groups(P>0.05).The egg diameter of the fertilized eggs in the feed DHA/EPA-1.34 group was the largest(P>0.05),which was significantly higher than that in the feed D/E-2.07 group(P<0.05).There was no significant difference with the other treatment groups(P>0.05).There was a significant correlation between DHA/EPA,DHA,EPA in the feed and the hatching rate of fertilized eggs.There was a significant correlation between the number of sigma n-6 in the feed and the number of zoea.There was a significant correlation between DHA/EPA,DHA,EPA in the feed and the metamorphosis rate of the nauplius.The proportion of DHA/EPA in fertilized eggs increased with the increase of the ratio of DHA/EPA in feed,and the ratio of ∑n-3/ ∑ n-6 was the largest in the control group,D/E-1.34 group followed,and was significantly higher than the other groups(P<0.05).The fatty acid composition in the tissues of the broodstock was basically the same as that in the feed.The proportion of DHA/EPA increased with the increase of DHA/EPA ratio in feed(P<0.05),and the ratio of DHA/EPA of females was higher than that of males.In conclusion,when the total amount of DHA and EPA is constant,the suitable dietary DHA/EPA ratio can increase the spawning effect of broodstock and the quality of eggs and larvae,but the male broodstocks may required a lower dietary DHA/EPA ratio than females.The DHA/EPA ratio of 1.34 in diets can significantly promote growth and gonadal development of females and increase fecundity.And a ratio of DHA/EPA of 0.47 can promote growth of males,increase the continuous spawning rate,the hatching rate of fertilized eggs and the metamorphosis rate of the nauplius.