In lake Izunuma-Uchinuma where invasive largemouth bass have caused serious environmental problems, various removal methods of the bass have been developed and introduced to control the bass population. The preliminary investigation revealed that abundant recruited bass fry showed diet shifts to piscivory at a small size (>20 mm FL (fork length)) and preyed vigorously on larvae of indigenous fish species. Therefore, it is important to prevent the reproduction of largemouth bass in order to conserve the indigenous fish fauna. To prevent the reproduction of bass, we were focused on the development of artificial spawning nest (ASN) that were able to be eliminated with the eggs of largemouth bass after their spawning in the nest was complete. Various prototypes of ASNs were devised and tested in the lake. In the tests, largemouth bass spawned most frequently in a type of ASN that was a cluster of gravel on a plastic tray surrounded by net screens on three lateral sides. Using this type of ASN, the control project of the largemouth bass population reduction in the lake started with volunteers in 2004. During this project, we needed to eliminate the eggs on the ASNs frequently (twice a week), because the spawned eggs in the ASN hatch and drop off a few days after the spawning. Under natural condition, hatched largemouth bass stay in a substrate for several days until they swim up into the water column. Then, we developed an improved ASN which could stock the hatched larvae of the bass in it. Another tray with fine mesh was attached to the bottom of the ASN and an attachment of a mesh tray under the ASN made it possible to stock the hatched bass for more than a week in the ASN. Therefore, the introduction of the improved ASN (double tray type ASN) reduced the collecting work to once a week and increased the number of eliminated eggs. Moreover, three additional tests were conducted to develop maintenance-free types of ASN. However, no successful result was obtained from these three test types of ASNs. Therefore, the double trays type of ASN is better in terms of cost and benefit. The double tray type of ASN has been adopted for the control project in the lake at the present.

Three invasive fish species, Largemouth bass Micropterus salmoides, Northern snakehead Channa argus, and Aucha Perch Coreoperca kawamebari, were collected at the Aichi Yahagi-furukawa River, Aichi Prefecture. Four of the nine Largemouth bass preyed on small fish or shrimp while other two species preyed on no bait.

We investigated the role of aquatic plants in the time-dependent change of dissolved oxygen (DO) volume by field surveys and experiments in Katano-kamoike, Ishikawa Prefecture, central Japan. Since the minimum volume of DO was recorded just before sunrise and the maximum DO volume was recorded at the time of culmination (the sun's high point) or just after it, the fluctuation of DO was thought to be influenced by photosynthesis and respiration of aquatic plants. Furthermore, results of the experiment revealed that submerged plants such as Rigid Hornwort Ceratophyllum demersum increased the volume of DO when light intensity was high and reduced the volume when light intensity was low. On the other hand, Water Chestnut Trapa natans usually played a roll in reducing the volume of DO rather than increasing it.

Abe-haze, Mugilogobiusu abei, a gobiid fish sometimes moves out of the water and can stay in air for a considerable time, especially in overcrowded conditions. Why do they emerge and stay in air? To investigate the reason, I made some observations about Abe-haze fish’s behavior in two types of test tanks with land. One tank has a slope which divides the water-body into two parts (lager and smaller). The upper part of the slope emerges from the water forming dry ground (=land). Under extremely high density in the smaller water-body, nearly 80% of the fishes emerged over the course of a day. And several days, some of them moved over the land and reached the other (lager) water-body. In another similar tank with land covering the part of the surface area, the population density was about one quarter. In this case landing was done quickly and more individuals remained in the water. These observations indicate that the Abe-haze fish emerges to avoid competition and that they may make excursion overland to find another water-body (tide-pool).

Individual growth was compared between Lefua echigonia (Japanese name: hotoke-dojo) and Lefua sp.1 (Japanese name: nagare-hotoke-dojo), both endemic and endangered species in Japan, using an individual identification-recapture method from November 1999 to December 2000 in each habitat of the Kako River, Hyogo Prefecture. Individuals of Lefua echigonia showed more rapid growth than Lefua sp.1 when comparing individuals of same range in standard length at the start.

The status and distribution of unionid mussels in Lake Kasumigaura was reported on in 1996. At this time the populations had recently decreased in the lake. In this study, the distribution of unionid mussels was investigated on the surface of dredged sediment in the Yogo-iri irrigation ditch connecting to Lake Kasumigaura. Distribution of Unio douglasiae was localized in a 1,000 m section of study site of the 3,500 m long ditch. In contrast, Anodonta spp. were widely distributed across the study site. Because many unionid mussels were captured in Yogo-iri irrigation ditch, the ditch is assumed to be refugia for the populations of unionid mussels in Lake Kasumigaura. Analyzing mussels on the surface of dredged sediment would be more convenient than using traditional methods to clear the distribution of unionid mussels.

We first documented the predation of a waterfowl chick by the largemouth bass although a few lines of circumstantial evidence have suggested this predation taking place in the past. We dissected a male bass (421 mm in standard body length) caught in Anjiki river, a small creek that flows into Lake Biwa, and found in the stomach an unimpaired chick (55.4 g in wet weight) of either Anas platyrhynchos, A. poecilorhyncha, or the hybrid.