| Discogobio yunnanensis is a small benthic fish,which is adapted to torrent environment.It is endemic to China and mainly distributed in Yunnan,Sichuan,Chongqing and Western Hubei.As its delicious and nutritious meat,it is very welcome to the consumers.However,the recent overfishing has lead to a rapid decline of wild population.Therefore,it is important to strengthen the investigation on the reproductive biology and fulfill the artificial breeding strategy.With this aim,we collected parental fishes in Daning River from June,2015 to June,2016,raised them in water-circular systems in our lab for experimental use.In the present study,we focused mainly on the reproductive biology of our cultured D.yunnanensis including breeding and embryonic development,gonadal differentiation,gonadal development and annual change of gonad,by using Microscope,artificial breeding technologies and corresponding analyses by series of softwares,such as Excel,Origin,SPSS,etc.The main results and conclusions are as follows:?1?Artificial spawning of D.yunnanensis was induced by using DOM combined with HCG and LHRH.The best Oxytocin combination was(HCG 8 IU·g-1&LHRH-A20.1?g·g-1&DOM 0.2 mg per tail),and either the combination of(LHRH-A2 0.1?g·g-1&DOM 0.01 mg per tail)or the DOM 0.01 mg per tail use alone can successfully induce spawning and oviposition as well,however,with lower hatching and survival rates.The above experminatal were carried out at 20?.?2?The diameter of mature egg of D.yunnanensis is 2.05-2.20 mm.It cost about168 h 30 min to finish the embryonic development under a water temperature of17-19?.The embryonic development of this fish can be divided into 27 development phases and 5 stages,including cleavage prophase stage?2 h 30 min?,cleavage stage?7 h20 min?,blastula stage?7 h 20 min?,gastrula stage?7 h 20 min?,and the organogenetic stage?127 h 3 min?.The newly hatched larvae have the rudiment of mouth,the gut,liver and mesonephric duct are initially form,and the average length,weight and yolk sac length are 7.16 mm,0.012 g,4.04 mm repectively.Compared to other fishes of Labeoninae,it is more easier for newly hatched D.yunnanensis larvae for its relatively completed development,.?3?At 20?,the first feeding occurred at 9 dah?day post-hatch?and feces discharges can be observed on that day as well.The yolk sac disappeared completely,and the larvae developed into juvenile stages at 28 dah.The bigger yolk sac can provide more nutrition for the larvae,which can avoid death caused by inadequate food intake so that can ensure the population continuity.?4?When the temperature of the water is?20±0.5??,primary gonads can be firstly observed in 18 dah larvae.The histological differentiation of ovary occurred at the 70 dph,with a obvious ovarian cavity and clustered oogonia,while the cytological ovarian differentiation,marked by the formation of primary oocyte,was observed at about 100 dah.On the other side,the sperm duct primordium and microvessel was observed at 110 dah,which indicate the start of the histoligical differentiation of testis,striped testis formed at 140 dah,and the primary spermatocyte formation marks the initiation of cytological testicular differentiation.Thus,differentiation of ovary is more earlier than that of testis in D.yunnanensis.?5?The ovarian development of D.yunnanensis can be divided into five different stages under cultured condition:ovary of single-layer follicular period from June to November,oocyte in phrase of yolk vesicle from December to March?next year?,the oocyte in phrase of yolk filled from April to May,the phase of mature oocyte from late May to early June.The ovary began to degrade at three to five days after ovulation,mainly in June.The gonad in stage?is the longest lasted period during all the year,the ovary was in stage?in winter,and matured in May and then spawned.?6?The testicular development of D.yunnanensis can also be divided into five different stages under cultured condition,growth of spermatocytes from June to December,and the main of spermatogenic cells was spermatogonia and primary spermatocyte.The maturation of spermatocytes from January to March in the next year,and the spermatogenic cells were mainly composed of spermatogonia,primary spermatocytes and secondary spermatocytes.The initial appearance of spermatoblast from March to April,the gonad was mainly composed of secondary spermatocytes and sperm cells.The complete maturation of spermatozoa from April to June,and the testis was full of sperms.The testis degraded three to five days after propagation.?7?The peak of average gonad somatic index of female D.yunnanensis was appeared in April-June?mainly in May?,which indicated the period of reproductive peak.The variation of the gonad somatic index of testis was similar to ovary.D.yunnanensis is a fish spawning only once per year,and it is the yolk deposition stage in January to April.Thus,increase the abundance of bait during this period may promote the gonadal development. |
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