| Japanese eel (Anguilla japonica) is one of the most important migratory fish in Asia,and a kind of high economic value fish in China, while all fries cultivated are wildelvers captured in estuaries. Because of the particular life history, artificial propagationof eels has gained international interests during the last century. In recent years, seedresources of eels suffered a serious recession by the unsustainable fishing methods. It’smore and more necessary to carry related research on reproductive and breedingtechnologies.This paper briefly reviewed and summarized the latest research on reproductive andbreeding technologies of Japanese eel, which covers stocks selection, artificial inductionof sexual maturation, feed and culture devices and methods for Japanese eel nursing.Comparison and analysis on the reproductive application of different environment (inthe recirculation system and in cement pond) was measured and analyzed with injectionby different hormone, dose and time. Based on the changes of individual appearance ofeels and features of ovary with histological section, we mainly elaborated histologicaland cytological characters at different development stages of ovary of the Japanesefemale eel by the artificial induction condition. Comparison and analysis on thegonadosomatic index (GSI) of different developmental ovary stages, this papermeasured and analyzed six biochemical components of the serum (total protein (TP),triglycerides (TG), total cholesterol (TC), blood glucose (Glu), calcium (Ca) andphosphorus(P))；the content and composition of amino acids in ovary, by medicalinspection methods during carp pituitary extract and HCG induced maturation of thefemale Japanese eel. The biological characteristics of embryo and the larva7daysincubation used by the methods of observing living body was roughly studied.The results showed that:(1) Injection with hormone a (0.4mg PT+0.35mg DOM+150IUHCG)/500g BW and hormone b (0.75mg PT+150IUHCG)/500g BW respectively, the eels of bothgroup got matured at56-80th day with ovary at Ⅴ period. There was some differenceabout GSI from constant injection group to gradient injection group. However, the rivereel can get matured in the same time by inducing with the hormone at the same totaldose: there was no significant difference (P>0.05) at70th day that GSI were25.0%and24.8%respectively. We can control the mature time by adjusting injection methodsfor the weekly injection group could get matured earlier than two-week injection group.Female eels can achieve the hydration by their own endocrine system, so we suspendedinjection during100to130d. The male eel can get plenty of sperm synchronization withthe matured female eel by weekly injection hormone b in the same condition for80~100d and4injection later after female injection.(2) The results showed that the gonad of treatment group got matured gradually during84days with GSI increasing significantly to (46.32±1.75)%at the12thinjection; whileGSI of the control group always stayed at (2.45±0.30)%. There was no differencebetween the TP level of treatment group and control group (P>0.05) which remainedrelatively stable. However, the blood lipid displayed significant difference (P <0.05)until56thday: TG and TC of the treatment group maintained a high level, averagerespectively (12.67±2.83) mmol/L and (15.54±3.01) mmol/L; while control groupkept with a low level, average respectively (6.33±4.14) mmol/L and (8.53±3.30)mmol/L. The Glu level of both groups carried on rising with a low level at early.Correlation analysis indicated that there was significant negative correlations betweenTG and GSI in treatment group (r=﹣0.732, n=6, P <0.01). Significant correlationswere found between Ca and GSI (r=0.961, n=6, P <0.01), P and GSI (r=0.775, n=6, P<0.01)in treatment group: as the growth rates of GSI, the level of Ca and P increaseddramatically from28thday, while the control group stayed at a low level.(3) The level of taurine displayed significant difference (P <0.05): treatment groupshowed a downward tendency which from phaseⅠ/Ⅱ(0.217±0.040mg/100g) to phaseⅣ/Ⅴ(0.102±0.045mg/100g); while the control group remained relatively stable (0.204±0.057mg/100g). The level of total amino acids carried on rising at phaseⅢ, andmaintained the same level at phase Ⅳ andⅤ; total essential amino acid proved thecoherent change with the percentage of total essential amino acid which was (48.633±0.913)%. Composition of AA in turn in treatment group from high to low wassignificant difference (P <0.05) average respectively: at phaseⅠ/ⅡGlu> Asp> Lys>Leu> Arg> Gly> Pro; at phase ⅢGlu> Asp> Leu> Lys> Pro> Arg> Gly; at phaseⅣ/ⅤGlu> Asp>Leu> Lys> Arg> Gly> Val. The control group stayed at phaseⅠandphaseⅡ: Glu> Asp> Lys> Leu> Arg> Gly> Pro. (4) Fertilized eggs were through a semi-dry artificial fertilization method: there were38h30mins from fertilized egg to larva (21±0.5)℃. The development characteristicof eel larva was different from those of most other teleosts: such as transparent bloodcell; S-transformer tubular heart; opening mouth, neuromast structures in certain daysand cilium movement in bowel.The above results suggested that there were certain features about the artificiallyreproductive and breeding technologies of Japanese eel: the river eel can get matured inthe same time by induring with the hormone at the same total dose; we can control themature time by adjusting injection methods. It turned out that there is a closerelationship between ovary development and lipid metabolism, and some inorganic ions(Ca, P) have played an important role in this process. According to the nutritionrequirement and metabolic rule of the female Japanese eel, it’s a new potential way forus to judge ovary developmental stages by measured and analyzed the level of bloodlipid or serum Ca and P. It turned out that there is a close relationship between ovarydevelopment and protein metabolism, and some key amino acids such as Taurine haveplayed an important role in this process. It’s a potential way for us to improve thenutrition of Japanese eel broodstock. These results indicated that there is a specialfeeding method and environment for Japanese eel larva for its special structure. |
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