COMPETITON BETWEEN MEDAKA (Oryzias Latipes) AND MOSQUITOFISH (Gambusia Affinis) UNDER DIFFERENT TEMPERARURES

摘要

Medaka (Oryzias latipes) is a native freshwater fish in Japan; while an introduced fish, Mosquitofish (Gambusia affinis) tends to expand and enters into habitat areas of Medaka, recently. In this study, cultivations of these fishes were conducted using laboratory scale under different temperatures, and observations and measurements were made for mortality rates and behaviors in co-residential and isolated cultures. Experimental results demonstrated that no deaths were observed in isolated cultures for each fish if the temperature was in the range of 16°C to 30°C. However, above this range, mortality rates of Medaka increased significantly in comparison with Mosquitofish. Moreover, in co-residential cultures of both fishes, Mosquitofish attacked Medaka directly, so that every Medaka died within a period of one or two weeks in the same temperatures range. In contrast to these results, Mosquitofish could not tolerate at low temperatures around 10°C or less, and was not aggressive in attacking Medaka. These results indicate that the invasion by Mosquitofish will be accelerated by global wanning.