Competitive interactions between the Australian native fish Galaxiasmaculatus and the exotic mosquitofish Gambusiaholbrooki,in a series of laboratory experiments

Competitive interactions between <i>Galaxias maculatus</i>, native to southeastern Australia, and <i>Gambusia holbrooki,</i> an exotic pest, were examined in relation to two types of artificial cover and a food source. Experiments were performed in an 800 l tank using photographic techniques. The relative distance of <i>G. maculatus</i> from cover or food source before and after the introduction of <i>G. holbrooki </i>were compared. Also, the proportions of the species were altered to examine the effects of unequal numbers on dominance behaviour. It was found that <i>G. holbrooki</i> was unable to out compete <i>G. maculatus</i> for either cover or food. The distance of <i>G. maculatus</i> from a food source was seen to increase following the introduction of <i>G. holbrooki</i>, when they outnumbered <i>G. maculatus</i> by 3 to 1. Although the distance from the food of<i> G.maculatus</i> increased following the introduction of <i>G. holbrooki,</i> in all cases the mean distance of <i>G.␣maculatus</i> from cover or food was less than that of G<i>. holbrooki</i>. Significant intra-species competition appeared to occur between <i>G. maculatus</i> and it may be that this competition had a greater effect than the competitive pressure <i>G. holbrooki</i> was able to place on the natives. This study revealed that the exotic pest species, <i>G. holbrooki,</i> could not out compete a small native Australian fish species.<br />