Reproductive dynamics of redbait, Emmelichthys nitidus(Emmelichthyidae), from south-eastern Australia

Abstract

Redbait, Emmelichthys nitidus, from waters adjacent to Tasmania, Australia, have a discrete spawning season extending over a 2–3 months period during the austral spring. The species is a batch spawner with asynchronous oocyte development and indeterminate fecundity, reproductive traits suitable for the application of the daily egg production method to estimate spawning biomass. Histological criteria derived for estimating spawning fraction implied that females spawn once every 3 days. The relationship between batch fecundity andweightwas linear with fecundity increasing at a rate of 186 oocytes per gram of ovary-free body weight. Overall mean batch fecundities ranged between 11,001 and 27,162 for eastern and south-western Tasmania, respectively, the marked difference reflecting the substantially larger fish present off the south-west. Size at maturity varied markedly by region; sizes at 50% maturity in males were 146mm for eastern and 244mm for south-western fish, and 157mm for eastern and 261mm for south-western females. The reasons for the dramatic regional differences in these parameters warrant further investigation but may indicate a level of discreteness between populations.