Reproductive anatomy of the Australian grayling, Prototroctes maraena Gunther

Gross anatomy of Australian grayling testes showed progressive enlargement from March to the peak of the spawning season in late April–early May. The single, left testis changed from a flat, translucent wisp of tissue consisting of an anterior and posterior lobe connected by a thin filament to a three‐dimensional mass of milky‐white tissue which filled the coelomic cavity. Spawning lasted 2 weeks and testicular regression was apparent by 8 May when the bilobed condition of the testis was noted. The testis cleared rapidly and resembled pre‐spawning conditions by mid‐June. Histological examination revealed that Australian grayling testes follow the pattern of teleost spermatogenesis whereby clusters of spermatogonia arise from resting germ cells and all of the cells within a given cluster mature at approximately the same time. The single left ovary of Australian grayling females showed a similar pattern of development, filling the body cavity with an average of 47 000 eggs of 0.9 mm diameter by late April–early May. Females exhibited swollen genital vents near spawning and males developed breeding tubercles which are illustrated by scanning electron micrograph.