Studies On Fertilization Biology And The Growth,Morphological Characteristics Of F₁by Epinephelus Moara（♀）×Epinephelus Septemfasciatus（♂）

Hybridization is the most widely used and effective way in aquaculture breeding.In order to obtain several grouper species which were fast growing, high diseasestolerance and good quality of meet, hybridization between Epinephelus moara(♀) andE. Septemfasciatus(♂) by artificial method was studied. The fertilization process, thegrowth and morphological characteristics of hybrid F1by E. Moara (♀)×E.Septemfasciatus(♂) were observed and studied, and compared with the parents. Theresults were briefly summarized as follows：1. The observation on the fertilization process of F1by E. Moara (♀)×E.Septemfasciatus(♂)The hybridization between E. moara(♀) and E. Septemfasciatus(♂) by artificialmethod was studied. The morphology of mature egg of E.moara and the fertilizationprocess of hybrid F1by E.moara (♀)×E.Septemfasciatus(♂) were observed by scanningelectron microscopy. The results showed that there were no significant differences in theprocess of fertilization between crossbreeding and inbreeding of these twospecies.Some reticulate structures with Criss-cross and uncertain towards were foundon the outer chorionic surface of E.moara.Vestibule, micropyle and micropore can beobserved in the micropyle area. When the mature eggs and sperms encountering, theyactivated mutually and caused a series of responses. During0~25seconds postinsemination, Sperm attaching to the micropyle of mature egg can be observed; During30~45seconds post insemination, the spermatozoon entering into the egg and obviouslyto see the flagellum from outside of micropyle; The fertilization cone was formed inmicropyle after the spermatozoon entering into the egg, the fertilization plug can beobserved around the fertilization cone, and closed the micropyle; During90seconds~3minutes post insemination, the egg surface began to repair. The polyspermy was not observed during the crossbreeding insemination.2. Observation of embryonic development, morphological development of larva,juvenile and young fish of crossbreed F1by E. Moara (♀)×E.Septemfasciatus(♂)Crossbreeding between Epinephelus moara and E. Septemfasciatus was conducted,the embryonic development, the growth and morphological characteristics of larva,juvenile and young fish of the hybrid F1were observed. The embryonic development ofthe hybrid F1was divided into cleavage stage, blastula stage, gastrula stage, neurulastage as well as organogenesis stage, under the sea water with temperature21~22.5andsalinity29, pH8~8.1, it required35h20min for the hybrid F1embryonic development:2-cell stage at1h post fertilization (pf);16-cell stage at2h25min pf; multi-cell stageat3h50min pf; high blastula stage at5h10min pf; middle gastrula stage at12h40min pf; embryo body stage at16h pf; closure of blastopore stage at17h50min pf;muscle burl stage at20h50min pf; brain vesicle stage at24h50min pf; crystal stageat31h05min pf; heart-beating stage at32h40min pf; hatching stage at35h10minpf; newly hatched larvae stage at35h20min. There was no obvious difference inembryonic development between crossbreed F1and Epinephelus moara except the timeof Heart-beating stage. Based on the features of the yolk sac, second dorsal fin spine,pelvic fin spine, scale and body color, the post embryonic development of the hybrid F1was divided into larval stage, juvenile stage as well as young fish stage, after58days,the juveniles completed metamorphosis and changed into young fish: The larvae rely ontheir yolk for nourishment before4rdday after hatching, after this the larval mouthopened on4rdday, metamorphosis completed on about (42±2) days after hatching andthe fish turned into juvenile, for about (58±4) days, the juveniles changed into youngfish. Moreover, the growth and development of larva, juvenile and young fish ofEpinephelus moara were investigated, compared with the hybrid F1in growth rate, theresults showed that the hybrid F1grows quickly.3. Effect of salinity on embryonic development and larval activity of F1by E. Moara(♀)×E.Septemfasciatus(♂)The incubation periods, hatching and deformity rate of the fertilized eggs and thesurvival activity index (SAI) of newly-hatched larvae of F1Epinephelus moara (♀)×E.Septemfasciatus(♂) were examined at salinities of5,10,15,20,25,30（natural seawatersalinities）,35,40and45. The results showed that the optimum salinity for hatching wasin the range of30~35,When the salinity was above35or below30,the hatching ratesdecreased and the percentage of abnormal larvae increased.The optimum salinity forlarval survival was between30and35, and the SAI values were respectively33.3±0.8 and24.1±0.2, When the salinity was above30or below35, both of the larvae survivalrates and the SAI values decreased.4. Comparative analysis of the morphological characteristics between hybrid F1by E.Moara (♀)×E.Septemfasciatus(♂) and the parentsThe morphological characteristics of hybrid F1by E. Moara (♀)×E.Septemfasciatus(♂) and the parents which were6months old were analyzed byconventional morphometrics and the cluster analysis. The result showed that thecharacteristics of body color of hybrid F1both like two parents and appeared to bemedium; Among twelve measurable and countable traits for hybrid index analysis,there were six traits approached to female parent, five traits approached to male parentand one trait was the same with parents. The result of cluster analysis showed that F1hybrid by E. Moara (♀)×E. Septemfasciatus(♂) was closed to female in the aspect ofmorphology.5. Comparative analysis of growth characteristics between hybrid F1by E. Moara (♀)×E.Septemfasciatus(♂) and the parents under artificial farming conditionsThe growth parameters such as the body length, body weight, growth index,condition factor and heterosis rate of hybrid F1by E. Moara (♀)×E.Septemfasciatus(♂)and the parents which were10to14months old under artificial farming conditions weremeasured, compared and analyzed. The optimum growth equations of3groups whichwere fitting the growth model were established. The result showed that the orders ofbody length and body length growth index were E. Moara (♀)×E.Septemfasciatus(♂)﹥E. Moara﹥E.Septemfasciatus, the hybrid F1had obvious heterosis in term of bodylength; The order of body weight was E.Moara﹥E.Septemfasciatus﹥E. Moara (♀)×E. Septemfasciatus(♂), E. Moara had the fastest increment in term of body weight, andthe weight growth rate was faster than other two groups after10months; The highestcondition factor was observed in E.Septemfasciatus among10to14months, and hybridF1was the second; E. Moara had the lowest degree in term of variation coefficient andthe heredity was stably. The heterosis rate on body length and body weight for permonth showed that hybrid F1had a significant heterosis in growth among14months.