Reproductive cycle of the fork-tailed catfish Arius graeffei Kner & Steindachner (Pisces : Ariidae) from the Clarence River, New South Wales

Abstract

A. graeffei breeds annually from early November to early December when water temperatures reach 26°C and daylength averages 13.7 h. The bulk of ovarian development is restricted to the 2 months before spawning; the rate of oocyte development varies substantially between individuals. Diameters of mature oocytes range from 11.0 to 13.7 mm (mean 12.2 mm). Fecundity ranges from 40 to 122 and is linearly related to fish length and weight. The sex ratio of the population studied was 0.82 with a preponderance of males. The pelvic fins of adult female A. graeffei are longer and more rounded than those of adult males, and have a hook-like thickening (clasper) on the dorsal surface which develops seasonally in association with the reproductive cycle. Although marine populations of A. Graeffei appear to undertake extensive anadromous migrations associated with breeding, no such movements were observed in the fluviatile population studied.