Stages of gonad development during the reproductive cycle of the blackfin snook, Centropomus medius Günther

The reproductive biology of the Blackfin snook Centropomus medius was studied to expand our current knowledge on its aquaculture potential. From April 2001 to November 2002, 301 females and 193 males were captured. A 1:1.6 (male:female) ratio was found. Gonadosomatic (GSI) and hepatosomatic (HSI) indices suggested that the spawning period (SP) extended from September to November, with peak spawning activity in September (GSI = 0.98% and HSI = 0.7%). The period of pre-gametogenesis extended from January to June. During the post-SP in December, 90% of oocytes were pre-vitellogenic and 10% were atretic. Histological analysis of gonads (haematoxylin-eosin, Sudan black B, Alcian blue PAS, Cleveland Wolfe) showed five stages of oocyte development, each occurring at a characteristic range of oocyte diameters (μm): (I) pre-vitellogenic (25-55); (II) cortical alveoli (56-250); (III) vitellogenic (251-340); (IV) maturation (341-645) and (V) atretic (21-100). Five reproductive stages were identified for testis morphology: (I) regressed; (II) early maturation; (III) mid-maturation; (IV) full maturation and (V) regression. The type of ovarian development in C. medius was identified as a group synchronous.