Comparison of food habits between native Amur three-lips (Opsariichthys uncirostris uncirostris) and non-native largemouth bass (Micropterus salmoides) in Lake Biwa, Japan

The Amur three-lips (Opsariichthys uncirostris uncirostris) is an endemic subspecies in Japan and native to the river systems of the Lake Biwa–Yodo River. The population of three-lips in Lake Biwa has decreased, primarily due to habitat degradation and introduction by competitive, non-native predators, such as largemouth bass (Micropterus salmoides). However, the effects of bass introduction on the three-lips are unclear. We investigated the food habits of the three-lips and compared them with those of sympatric non-native largemouth bass in Lake Biwa. A total of 145 three-lips and 178 largemouth bass were sampled during the summer and fall of 2013. Fish prey, particularly ayu (Plecoglossus altivelis altivelis), was predominant in the three-lips diet, followed by terrestrial insects. Decapods (i.e., prawn and shrimp), ayu and demersal fish (e.g., gobids) composed a substantial proportion of bass diets. No significant dietary overlaps were found between the two predators. Our results suggest that differences in food habits between the two species may result from differences in feeding behavior; the three-lips is a mobile predator that forages mainly on nektonic and suspended food, whereas largemouth bass is an ambush predator that forages on both nektonic and benthic prey. We referred the results of three-lips diets in Lake Biwa in a previous study and suggest that changes in fish fauna, due to introduction by non-native largemouth bass, may have affected prey availability for the three-lips. Food habits of native Amur three-lips (Opsariichthys uncirostris uncirostris) were significantly different from non-native largemouth bass (Micropterus salmoides) in Lake Biwa, Japan. However, changes in fish fauna of the Lake, due to predatory impacts by non-native bass, may have affected preferable prey availability for the three-lips.