东太平洋赤道海域茎柔鱼体征生长及生殖投入

现生头足类的性腺发育滞后于个体生长,研究其生殖投入方式对于掌握它们的生长发育过程有着重要的意义。为此,本实验利用形态学和残差指标分析方法,对东太平洋赤道海域茎柔鱼的体征生长及其生殖投入进行了分析。结果显示,雌、雄个体均为匀速生长,雌性个体性腺成熟的最小胴长和最小体质量分别为270 mm和766 g,雄性个体性腺成熟的最小胴长和最小体质量分别为270 mm和479 g。雌、雄个体的空胃率低,摄食等级以1～2级为主;随着月份推移,个体的体征质量逐步趋好,在性腺发育阶段最差。雌性成熟个体的性腺指数平均值为2.26%±1.33%,缠卵腺指数平均值为34.34%±18.62%;雄性成熟个体的性腺指数平均值为1.31%±0.35%。雌、雄个体二者的体征指标与生殖投入指标均呈显著的正相关关系;随着性腺发育,体征指标和生殖投入指标呈下降趋势;随着胃饱满度等级增加,体征指标呈下降趋势,生殖投入指标则呈上升趋势。研究表明,茎柔鱼在性腺发育过程中持续摄食生长,生殖投入倾向于外源性,肌肉组织存储能量部分转化以满足生殖发育所需。

Body condition and reproductive investment of Dosidicus gigas in the equatorial waters of eastern Pacific Ocean

Extant cephalopod species are characterized by the lag of sexual maturation, when compared to their body growth. And they have evolved a range of flexible reproductive strategies, which are associated with different characteristics of body growth and reproductive investment, and the latter is vital to understand their reproduction. In this study, the specimens of Dosidicus gigas, collected from equatorial waters of eastern Pacific Ocean during a jigging fishery period from February to April 2017, were used to explore their body condition and reproductive investment, by applying methodologies of morphometric measurement and residual index analyses. Both female and male individuals were found isometric growth, according to weight-length relationship analysis. Female D. gigas attained maturation from mantle length (ML) of 270 mm and body weight (BW) of 766 g; whereas, males were found maturity from 270 mm ML and 479 g BW. Both female and male individuals had the lowest rate of zero stomach fullness degree (FD), with the majority being found at FD of 1-2. Along with the sampled months, D. gigas showed a better body condition, which was the worst during the sexual maturation period. The gonadosomatic index (GSI) was measured a mean value of 2.26%±1.33% for sexual mature females, and nidamental index was estimated at 34.34%±18.62%. Mature males had a mean GSI of 1.31%±0.35%. The body condition indices, measured as the standardized residuals of body weight and mantle length relationship, and reproductive investment indices, measured as the standardized residuals of reproductive system weight and mantle length relationship, showed a decreasing trend with sexual maturation. When corresponding to stomach fullness degree, the body condition index showed a decreasing trend, whereas the reproductive investment index increased with higher stomach fullness degree. However, there was a significantly positive relationship between indices of body condition and reproductive investment. Therefore, these evidences indicated that D. gigas continue feeding during sexual maturation, and the energy sourcing for reproduction is mostly from food intake. Meanwhile, energy reserve in the muscle tissues might be mobilized to meet the high energy demand during gonadal development.