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.