Reproductive characteristics of Patagonian longfin squid (Doryteuthis gahi) in the Southwest Atlantic Ocean

As the coldest water spawning species among the loliginids, Patagonian longfin squid (Doryteuthis gahi) plays an important ecological role in the Southwestern Atlantic Ocean ecosystem. However, the information on reproductive biology of this species is very limited. So the reproductive characteristics of D. gahi in the southwest Atlantic Ocean, including the sexual structures, gonad development and reproductive investment were studied based on the biological measurement and statistical analysis. The results indicated that the overall sex ratio of females to males was about 1.79∶1 and the ratio was not significantly away from the hypothesis of 1∶1. The size-frequency was unimodal for both sexes in dorsal mantle length and body mass, and no significant difference of growth between females and males was determined according to the length-weight relationship analysis. In females, the gonadosomatic index (GSI) ranged from 0.11 to 6.44, and the nidamental gland index (NGI) ranged from 10.74 to 36.51. There was significant correspondence between these two indices. In males, the GSI ranged from 0.29 to 5.75, and the spermatohporic complex index (SCI) ranged from 0.06 to 1.21. However, there was no statistical correlation between these two indices. The condition (defined as the residuals from the body weight-dorsal mantle length relationships) of females decreased with maturity, while the reproductive investment (defined as the residuals from the reproductive system weight-dorsal mantle length relationships) increased with sexual maturation onwards. In contrast to females, the condition of males increased with maturity, while the reproductive investment decreased during the course of sexual maturation. Though a slightly negative relationship was found between the condition and reproductive investment for both sexes, the condition was not significantly correlated with the reproductive investment. These findings implied that sourcing energy for reproduction in D. gahi might be mainly on exogenous, and the reproductive strategy was more inclined to the intermittent spawning strategy.