Life history traits of the pagrinae sparid Argyrops bleekeri inhabiting bays in Okinawa Island, Ryukyu Archipelago, southwestern Japan

Abstract

Accurate descriptions of life history profiles are important for effective conservation and stock assessment efforts. We examined the reproductive cycle, sexual maturity, sexuality, growth, and longevity of the pagrinae sparid Argyrops bleekeri inhabiting bays in Okinawa Island, Ryukyu Archipelago, southwestern Japan based on gonadal histology and age determination, using sectioned otoliths. The overall sex ratio was not significantly sex-biased. The spawning season was estimated to occur from November to June, peaking from January to May. Opaque zones can be considered an annual ring formed from November to March. The three growth parameters of the von Bertalanffy growth equation were L∞=43.1, K=0.245, and t0=−1.503 for females and L∞=46.8, K=0.261, and t0=−0.671 for males. Their growth was rapid during the first 3 years of life and reached a size of >30 cm, and then the males grew larger than the females. The maximum ages observed were 19.3 years for females and 17.4 years for males. The observed lengths at 50% maturity were 20.0 cm fork length (FL) for females and ≥18.0cm FL for males, which was already reached at 2 years old (females) and 1 year old (males). Transitional gonads were not observed. The species also had similar size and age ranges for both sexes. These results imply that the species may not undergo a sex change. Thus, the life history traits of A. bleekeri are characterized by functional gonochorism (juvenile hermaphroditism and/or gonochorism), relatively early maturation, and a long life span.