Seasonal changes in testicular histology of brown bullheads, Ictalurus nebulosus Lesueur

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Abstract
The seasonal changes in the cytology of the anterior spermatogenic testis permitted the reproductive cycle of I. nebulosus Lesueur to be divided into 4 periods: a prespawning period (mid-April to June), associated with an increased gonadosomatic index (GSI), when the overwintering secondary spermatocytes matured into biflagellate spermatids and spermatozoa and there was an increased vacuolation of Leydig and Sertoli cells; a spawning period (June to mid-July), associated with a fall in GSI, when Leydig cell vacuolation was maintained, Sertoli cell size and vacuolation became maximal and spermatozoa were released; a postspawning period (mid-July to mid-Aug.) characterized by an increase in spermatogenic activity, and ending when the seminiferous tubules were filled with secondary spermatocytes; and a resting (overwintering) period (mid-Aug. to mid-April) when the seminiferous tubules were filled with secondary spermatocytes; quiescent spermatogonia were evident in decreasing numbers, and Sertoli and Leydig cells were small and apparently inactive until late in the period. The posterior glandular testis similarly exhibited seasonal changes in size and vacuolation, with peak activity associated with the spawning period.

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