Reproductive biology and endocrinology of female red gurnard, Chelidonichthys kumu (Lesson and Garnot) (family Triglidae), from the Hauraki Gulf, New Zealand

Abstract

Red gurnard, Chelidonichthys kumu, were sampled by long-lining and from a fish processing factory to investigate the seasonal cycle of reproduction in a population from north-eastern New Zealand. Female red gurnard showed changes in gonadosomatic index (GSI) and frequencies of stages of ovarian development consistent with spawning from spring (September) until autumn (May). Peak GSI (approximately 6%) occurred in late spring or early summer, and minimum GSI (approximately 1%) occurred in winter (June). Blood samples were taken from live fish caught on long-lines, and seasonal changes in plasma concentrations of oestradiol-17ß (E₂) and testosterone (T) were measured by radioimmunoassay. Plasma E2 and T reached maximum concentrations of 1.99 ng mL^-1 and 2.06 ng mL^-1, respectively, as GSI levels peaked, and then declined as GSI decreased over summer. Plasma E₂ and T increased again as GSI began to increase prior to the next spawning season. Maximum hepatosomatic index (HSI) occurred in association with gonadal recrudescence. HSI decreased significantly as the spawning season progressed and showed a significant but irregular increase as recrudescence occurred prior to the following spawning season.