The biology of the opalfish Hemerocoetes monopterygius (Bloch and Schneider) in Wellington Harbour, New Zealand

Abstract

Major aspects of the biology of the opalfish - Hemerocoetes monopterygius (Bloch and Schneider, 1801) trawled from Wellington Harbour, New Zealand are examined. 2322 specimens were used. Analysis of 251 stomachs showed that H. monopterygius feed on a wide variety of benthic organisms - polychaetes and teleosts contributing the largest bulk. Males and females displayed allometric growth throughout the year. The fish appeared to be in better condition during the summer, autumn and winter months, the drop in condition in the spring months being correlated with the occurrence of spawning during these months. Ageing was by means of scales and otoliths. Ageing results along with length and weight measurements revealed a clear difference in growth between males and females, the growth pattern being adequately described by the von Bertalanaffy growth equation. Using a percentage point classification scheme H. monopterygius was determined to spawn in the harbour during late winter-spring. Evidence indicated H. monopterygius to be a protogynous species. The fecundity of the fish varied from 3006 at a length of 8 cm to 10,752 at a length of 16 cm. Parasites infecting the opalfish were a nematode - Philometra sp.b and a nematode larva belonging to the order Camallanata. An estimation of the Wellington Harbour population of H. monopterygius was made giving a figure of 636,827 for July.