Estimating gonadal development using a non-destructive measurement of ovarian length in live Tasmanian striped trumpeter,Latris lineata(Forster, 1801)

Abstract

Sexually mature female striped trumpeter Latris lineata (Forster, 1801) were sampled monthly for two spawning seasons until the start of gonadal recrudescence, and then fortnightly until ovulations ceased. Oocyte size and ovarian length, measured by inserting a semi-rigid biopsy catheter to the full extent of insertion, were recorded at each sample time. Ovarian length was expressed as proportion of fork length to provide a gonad index (GI). In non-ovulating females, there was little change in GI throughout the year. However, in ovulating females, GI increased from 18.3 five months before the first spawning season to 27.6 at the peak of the season in October, decreasing to 19.1 the following May and then increasing again to a maximum of 31.1 the following October, in concert with annual changes in reproductive condition. There was a positive linear correlation between GI and oocyte size during the period of oocyte growth (r = 0.75, n = 302). Based on the range of GI values for each stage in oocyte development (primary, cortical alveoli, vitellogenic, maturing and hydrated), GI was 90% accurate at assessing fish as pre-vitellogenic and 83% accurate at assessing fish as undergoing final oocyte maturation. This study demonstrated that measurement of GI by catheterization provides a rapid and non-destructive method for assessing maturational status of striped trumpeter broodstock.