| Japanese eel(Anguilla japonica)is a kind of typical species of marine spawning fishes that occupy a large share of the East Asian aquatic trade.In this paper,the research on the artificial propagation of eel in China and abroad,and the field investigation of the life history of eel,and the cultivation techniques of eel larvae,all of which were summarized,and the artificial propagation of eel and the characteristics of larvae initial diet and behavior morphology were explored.The final stage of maturation was divided into several phases to find the optimal timing of injecting hormone to induce the ovulation of the broodstock successfully.The different types of food were prepared,and the effects of different diets on survival of eel larvae were analyzed and compared.The morphological and behavioral characteristics of eel larvae were observed and recorded by microscope and video recording.The main findings are as follows:1.In order to solve the problem of eel broodstock dystocia,low ovulation rate and low quality of eggs,the number and size of lipid droplets in the process of oocytes development were studied to determine the developmental phase of egg cells and oxytocin to determine the relationship between ovulation and egg fertilization of females,and to estimate the optimum timing for injections of carp pituitary extract(CPE)for priming and 17?-hydroxy progesterone(OHP)for spawning induction.It was found that the oocytes were divided into 11 phases according to the size and number of lipid droplets.The results showed that when the oocytes were mature,their diameter became larger,the number of lipid droplets became smaller and the diameter became larger.The injection for priming was conducted at the 2-4th phase,and the injection for spawning induction was conducted at the 5-6th phase,which can promote the eel to lay eggs,and the oocytes can be effectively fertilized.Dystocia female ovary in the stage of ovarian cells varied greatly,and lipid droplets dispersed.The results showed that it is important to divide the number of the lipid droplets and the size of the diameter of the oocytes to the final maturation stage of the eggs.It is effective to improve the quality of the eggs of eel by selecting the optimum injection time,and promoting its ovulation.2.In order to explore the behavior and morphological characteristics of eel larvae,microscope observation and video recording was used in this experiment.It was found that larvae eyes began pigmented at 6dph,and tooth prototype began to appear.The tooth of larvae at 9dph was sharp and its surface was smooth and had no special structure.The larvae were suspended in the upper layer of water before 6 dph,and at 7 dph began to sink,and then mainly in the middle and lower water activity.Larval fish moved irregularly,and escaped from lightness,swam agilely.Larvae were observed deformities at 9-10 dph.3.The effects of different diets on the survival rate of larvae of Anguilla japonica were studied in this experiment.Compared with the control group(no feeding),the results showed that the shark eggs,krill extract-based diet and shark eggs,jellyfish-based diet and exclusively microalgae had positive effects on larval survival.However,the shark eggs,artemia-based diet and artemia,krill extract-based diet,rotifers and kelp,seaweed homogenate,jellyfish and fermented shark flesh reduced larval survival.Larvae fed the shark eggs,krill extract-based diet could live up to 20 days.To sum up,in the process of artificial propagation of eel,it is necessary to grasp the optimum inducing time of broodstock to improve the ovulation rate and egg quality.In early stage of larvae,we must strictly control the water quality,adjust the light,salinity,temperature and other factors to improve the survival rate of larvae.In addition,in this study,the initial diets of eel larvae need further in-depth exploration,and larvae breeding technology also needs to be improved. |
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