Sexual Dimorphism in Morphological Traits and Female Individual Fecundity of Odontobutis obscurus

We measured the sexual dimorphism in morphological traits,including the body length,head length,head width,head depth,snout length,postorbital head length,eye diameter,interorbital width,body depth,caudal peduncle length,caudal peduncle depth,caudal fin length,dorsal fin precoxal length,dorsal fin coxal length,length between dorsal fin,pelvic fin precoxal length, length between pelvic fin and anal fin,body mass,carcass mass of the Odontobutis obscurus in reproductive season from Caoejiang River,Shangyu City,Zhejiang Province.It had been found that the number of adult males was larger than that of females and the body length of adult females was significantly shorter than that of adult males.The females with special body length were significanlty shorter than the males in head length,head width,head depth,interorbital width,caudal peduncle depth and dorsal fin coxal length, carcass mass of adult females were significantly smaller than those of adult males,while the former were significantly larger than the latter in body depth,dorsal fin spacing,length between pelvic fin and anal fin.There was no significant sexual difference among other morphological traits.A principal component analysis resolve three components(with eigenvalues≥1) from ten size(body length)-free morphological variables,accounting for 61.6%of variation in the original data.The first component(26.9%variance explained) had high positive loading for size-free values of head length,head depth and carcass mass,the second component(18.3%variance explained) had high positive loading for size-free value of dorsal fin coxal length,and had high negative loading for size-free value of length between dorsal fin,the third component(16.4%variance explained) had high positive loading for size-free value of body depth and length between pelvic fin and anal fin.Females had significantly lower scores on the first and second axis,but had larger scores on the third axis of a principal component analysis than did males.The individual fecundity was significantly positively correlated with the body length and body mass in O obscurus.A partial correlation analysis showed that the individual fecundity was positively correlated with body mass and negatively correlated with the body length when the third invariableness was in control.A conclusion has been drawn that adult females increase the individual fecundity through increasing the individual size(especially through increasing the body mass) and capacity of abdominal cavity,thus increasing reproduction output.