Life history pattern and feeding ecology of the introduced eastern mosquitofish, Gambusia holbrooki, in a thermal spa under temperate climate, of Lake Hévíz, Hungary

Abstract

The life history pattern and feeding ecology of introduced eastern mosquitofish was studied in Lake Heviz, an extreme thermal habitat under temperate climate. There was a marked difference in the size distribution, sex ratio and diet composition of fish between the lake and the mudholes along the shore line. The sex ratio was 1:8 and 2:1 in the lake and in the mudholes, respectively. The smallest male with gonopodium was 12.9 mm and the smallest female with embryos was 13.2 mm, suggesting a very early maturity in both sexes. From April to July almost all females were pregnant, but from August the ratio of pregnancy started to decrease and it was only 18% in late September. The average brood size per female reached a maximum in the beginning of May when the largest overwintered females were reproducing. From the end of May to the middle of September the mean brood size stabilised within a very low embryo per female range. The diet of eastern mosquitofish consisted of aquatic- and terrestrial invertebrates, filamentous algae and detritus. Rate of cannibalism was 1%. The diet of fish showed significant temporal and spatial differences. However, most of the size and sex dependent variations in the diet could be due to different habitat use of juveniles, males and females. Feeding strategy analyses suggested a high individual specialisation, and thus an opportunistic feeding strategy for eastern mosquitofish both in juvenile and adult stages.