Reproductive biology of Rhabdosargus sarba (Sparidae) in Western Australian waters, in which it is a rudimentary hermaphrodite

The reproductive biology of the tarwhine Rhabdosargus sarba has been studied in three very di¡erent environments in Western Australia, namely the lower reaches of the Swan River Estuary and marine waters at the same latitude, i.e. *328S, and a large subtropical marine embayment (Shark Bay) approximately 800 km further north. A macroscopic and histological examination of the gonads demonstrated that R. sarba is typically a rudimentary hermaphrodite in Western Australian waters, i.e. the juveniles develop into either a male or female in which the ovarian and testicular zones of the gonads, respectively, are macroscopically undetectable.This contrasts with the situation in the waters o¡ Hong Kong and South Africa where R. sarba is reported to be a protandrous hermaphrodite. Although R. sarba spawns between mid-late winter and late spring in each water body, the onset of spawning in the estuary is delayed until salinities have risen well above their winter minima. Although males and females attain sexual maturity at very similar lengths in the Swan River Estuary and Shark Bay, i.e. each L50 for ¢rst maturity lies between 170 and 177mm total length (TL), they typically reach maturity at an earlier age in the former environment, i.e. 2 vs 3 years old. During the spawning period, only 25 and 12% of the males and females, respectively, that were caught between 180 and 260mm TL in nearshore marine waters were mature, whereas 94 and 92% of the males and females, respectively, that were collected in this length-range over reefs, were mature. This indicates that R. sarba tends to move o¡shore when it has become ‘physiologically’ ready to mature. The L50s at ¢rst maturity indicate that the minimum legal length inWestern Australia (230 mmTL) is appropriate for managing this species.