Histology of gonad tissue in a sequential hermaphrodite fish

Histology of gonad tissue in a sequential hermaphrodite fish

The hogfish (Lachnolaimus maximus) is a sequential hermaphrodite. It is protogynous: on reaching sexual maturity hogfishes are all female, and transition to male on reaching a size of 30cm (at about 3 years of age). This transition is marked by a change in coloration (from drab and tan to orange with dark bands) and a major restructuring of gonadal tissue as it transforms from ovaries to testes. However, the histological changes associated with this transition have not been sufficiently documented. Therefore, hogfish gonad histology was examined in relation to fish length, age, condition, and coloration. Hogfishes were collected by spear gun from local reefs, weighed, measured, and the gonad tissue excised and stored in formalin. Samples from the center of the gonad were dehydrated in EtOH, embedded in histological media, sectioned along the transverse plane, mounted onto slides, and stained with hematoxylin and eosin. Sections were then mounted on slides and scanned for germ cell development, appearance of the tunica albuginea, and formation of atretic bodies. Oocytes were counted and their stage noted, along with the presence of postovulatory follicles. When spermatogenesis was noted, the specific stage was recorded. Data were collected semi-quantitatively based on observations of the first 200 cells on each slide. These results were analyzed in the context of the morphological transition in hogfish size, condition, and coloration.