Testicular maturation and regression in the common snook

During the annual reproductive cycle, the lobular testis of Centropomus undecimalis undergoes height, width, and morphological changes which reflect five reproductive classes: regressed; early, mid-, and late maturation; and regression. Histological criteria, particularly differences between continuous and discontinuous,germinal epithelia, are used to distinguish these five classes, even though they are only reference points within the annual gonadal cycle. A mechanism for lobular growth during early, mid-, and late maturation is presented; and it is hypothesized that a permanent germinal epithelium first appeared in the fishes. Throughout the year, periodic acid-Schiff-positive macro-melanophage centres and PAS-positive granulocytes are observed in the testis. They are most abundant after the breeding season, and they may be involved in focal tissue degradation. (C) 1998 The Fisheries Society of the British Isles.