The mechanism of gonadal development in response to environmental factors in dwarf-form individuals of female Sthenoteuthis oualaniensis in the South China Sea

The gonadal development (GD) of cephalopods is highly sensitive to the environment. To explore the relationship between the GD of dwarf-form individuals of female Sthenoteuthis oualaniensis (S. oualaniensis) and the marine environment, this study used statolith age and analyzed the relationship between GD and the marine environment using a generalized additive model (GAM) for S. oualaniensis samples collected in the South China Sea from January-April and September-December 2019. The results showed that the age at first sexual maturity of dwarf-form individuals of female S. oualaniensis in the South China Sea was approximately 143 d. Sea surface temperature (SST), sea surface salinity (SSS) and chlorophyll a concentration (Chl), taken at the same time and for the same area as the sample individuals, were three environmental factors (EFs) that significantly affected the gonadosomatic index (GSI) and reproductive investment index (RI) of dwarf-form individuals of female S. oualaniensis. For the GSI, the model explained 90.5% of the overall variation, and the s (SSS) term had the largest impact on the GSI. For the RI, the model explained 91.8% of the overall variation, and the s (SST) term had the greatest effect on the RI. The GD of dwarf-form individuals of female S. oualaniensis exhibited a range of adaptation to the three EFs. SST had a promotional effect at 26.0-27.7 degrees C, SSS had a promotional effect at 33.0-33.5, and Chl had a promotional effect at 1.0-2.1 mg L-1.