The use of a point-count technique to quantify the egg assemblage in Melicertus plebejus (Hess, 1865) ovaries

Abstract

We tested the hypothesis that cellular-type composition of eastern king prawn ( Melicertus plebejus) ovaries varies in space and time along the coast of New South Wales (NSW), Australia. The ‘point count technique’ commonly used in ecological studies but rarely in studies of reproductive biology was used to describe the oocyte composition of ovaries. Within Times there were differences in the cellular-type composition between Locations (Global R = 0.357 and 1% significance). Most dissimilarity was in pairwise comparisons between the southern most and each of the other locations ( R values 0.2–0.6, P = 0.001). Within Locations there were differences in similarity between Times (Global R = 0.214 and 0.1% significance). Most dissimilarity occurred in pairwise comparisons between winter and summer ( R values 0.36–0.45, P = 0.001). Females capable of spawning are found across the latitudinal range of the main offshore prawn fishing grounds but the main spawning area is in the north and whilst these females occur year around, we did not detect evidence of winter spawning in waters off NSW. As part of the sampling strategy, we were able to show that macro-staging of ovaries is satisfactory for distinguishing between yolked and unyolked eggs in eastern king prawns and for identifying females capable of spawning.