Study On The Reproductive Biology And Resource Enhancement Of Megalobrama Skolkovii In Xujiahe Reservoir

Annuli feature,age structure,growth character,reproductive strategy and histological gonad development of Megalobrama.Skolkovii were studied,basing on 165 specimens collected from September 2007 to July 2008,in Xujiahe Reservoir,Hubei Province,China.Technical measures on realizing population enhancement for M. Skolkovii were discussed.The main results were summarized as follows:1.The character of annuli on scale was a typical "loose-close and cut" pattern.Cut could be seen obviously in pro-lateral zone,and different loose-close rings were appeared in back-lateral zone.The false ring and spawning check were seen occasionally,while first check had not been found in juvenile fish.2.Scale was used for age determination.Samples were consisted of 1 to 6 year,six age-group composition,dominating by 3 and 4 year individuals accounting for 71.05%, but few juvenile fish of 1 and 2 year.The body length and body weight of all specimens ranged from 163 to 380 mm,and 95 to 1200 g,respectively.Relation between body length and body weight of M.Skolkovii was W=2.23×10^-5L^3.0057,with no significant difference among males and females.3.The growth showed an isometric pattern,so that it could be described by von-Bertalanffy equation.Growth formulas were L_t=458.35[1-e^{-0.1802(t+0.1729)}]and W_t=2197.30[1-e^{-0.1801(t+0.2889)}]^3.0057.The inflexion age of body weight growth was at 5.9 years,and corresponding theoretical values of body length and body weight were 306.5 mm and 671.2 g.Compared with other geographical populations that had been studied,M. Skolkovii in Xujiahe Reservoir had a higher inflexion age,but relatively lower asymptotic body length and body weight,growth coefficient and performance index,which led to a more slowly growing in the whole.4.Age at sexual maturity was different between male and female.Males reached maturity at age two,while females at age three.The minimum size of adult male was 225 mm in length and 300 g in weight,that of adult female was 233 mm and 320 g. Gonadosomatic index(GSI) in both sexes had nearly the same trend for annual change, only one peak area occurred in April to July.The individual absolute fecundity(F) varied from 49 to 255 thousand eggs,with an average of 139 thousand.The individual relative fecundity by body length(F_L) and body weight(F_W) were 195.6 to 720.1 eggs per millimeter,462.1 on average;162.3 to 479.6 eggs per gram,313.3 on average.Individual fecundity had more significant correlations with four biological indicators;they were body length,body weight,gonad weight and maturation coefficient.5.The histology of gonad development and different phase of germ cells were observed.Gonad development of M.Skolkovii could be divided into six stages,Ⅰ～Ⅵ. Oocytes developed synchronously from phase 3 to 4.The histological structure of ovary and testis went back to stageⅡafter reproduction,and by a slight growth they came to stageⅢduring winter.6.The reproduction season for M.Skolkovii started from end of May and went down to beginning of July,with a peak in June.The natural spawning ground could change place to place due to the hydrology.It usually located in the river-way from upriver where had flowing current.The spawning pattern was synchronous in batches,and spawned once in a year.7.With the signature of less junvenile fish population,low individual fecundity and individual miniaturization,the resource of M.Skolkovii in Xujiahe Reservoir is facing a trend of deterioration.This was probably determined by complexed factors,such as low abandunce of preferred diet,food competition among interspecies,prediction by predators, envionroment variation and consistant fishing.According to the analysis above,the suggestions by restricting capture standard,strengthening protection of reproduction,and using selective improved variety were proposed on resource enhancement of M.Skolkovii.