This paper reports the results of research on largemouth bass living in the Aokata Dam on Nakadoorijima of the Goto Islands in Nagasaki Prefecture. The breeding season was found to be from April to May. The bass prey on the arthropod Asellus hilgendorfii, about 1 cm in the total length, as their main food source independent of bass size (length) and season. This appears to be a result of the scarcity of food for bass in the Aokata Dam. Sexual maturity in bass from this population appeared to be achieved at 4 to 5 years of age as determined by GSI and otolith age assessment. This result showed that the growth of the Aokata Dam bass was very slow compared with that seen in previous work on largemouth bass.