Takeshita Naohiko

Characteristics of the feeding behavior and relationship between the standard length (SL) and the size of scrape marks of ayu Plecoglossus altivelis altivelis were studied using 123 cultured specimens in aquaria. Feeding behavior was observed individually, 116 specimens (94%) have mouth laterality for feeding. Also, feeding behavior were found two types. The first was eating the algae directly from the shelter in 91 specimens (78%). The second left the shelter and ate the algae after changing direction back to the shelter (22%). One side of the lower jaw when feeding on the acrylic plate side was turned downward and the other side of the jaws was closing. On the scrape marks, 11 to 14 and 11 to 13 level lines were visible caused by the upper and lower jaws and the algae was not scraped between the upper and lower parts. The comb–like teeth groups are arranged as 13 to 14 rows and 12 to 14 rows on the upper and lower jaws, respectively. Therefore, it is suggested that they use almost all of the comb–like teeth groups except the back teeth row on the upper and lower jaws for feeding. The lengths of upper and lower jaws were found to have power regression with the SL, respectively. Also, the relationship between the SL and full width of the scrape marks (FWSM) was： FWSM = 0.3939SL^0.6767 (R^2= 0.8392, 64-212 mm SL).

Effects of water temperature on feeding and growth of the 0-year-old catadromous fourspine sculpin Rheopresbe kazika were studied using 8 different temperatures from 12 to 26℃ for 60 days. At each of the 8 temperatures, 20 fish were reared in aquaria. In the ranges of 16 to 24℃ and 22 to 26℃ the daily growth rate and daily feeding rate, respectively, were higher than the others. Also, the optimal water temperatures were calculated 19.6℃ for daily growth rate and 25.5℃ for daily feeding rate. The optimal water temperature for daily growth rate was lower than that for daily feeding rate. While, feeding efficiency were showed high values in the range from 12 to 22℃. These results indicate that the optimal water temperature range is from 16 to 22℃, and that a water temperature of 12℃ is too low and above 24℃ is too high for sustainable growth during culture of R.kazika.

Growth of immature Lates japonicus in eelgrass (Zostera japonica) beds of the Tomouchi River located at around 4.3 km upstream from the river mouth of the Gokase River, Kyushu Island, Japan was studied by the mark and recapture method and scale reading from September 1998 to March 2004. Newly occurring 0-year-old L. japonicus specimens of 13.9–78.0 mm SL (standard length) in Z. japonica beds of the Tomouchi River in August or September reached sizes ranging 58.8–125.7 mm SL by April and 203.4–232.8 mm SL between October and November of the following year. Monthly changes in specific growth rates of individuals demonstrated that rapid growth months of immature fish were limited to the period of high water temperature (22–28℃) from June to October. Also, it was supposed that the large-sized fish of the 0-year-old fish migrated away from Z. japonica beds after December, however a few fish remained in Z. japonica beds until the following November.

The Japanese lates, Lates japonicus is an endemic fish to the Pacific coast of southern Japan, and commonly found in estuaries and coastal waters of Miyazaki and Kochi Prefectures. The larvae, juveniles and young fish stay in the eelgrass, Zostera japonica beds in brackish water areas. Effects of water temperature and salinity on feeding and growth of immature L. japonicus were studied using combinations of seven levels of temperatures (16 to 28℃) and 6 different salinities (9 to 34 ppt) over two experimental periods each of 30 days. At each of these conditions, ten fish were reared in aquaria for periods of 30 days. Based on values of the daily feeding rates, specific growth rates and feeding efficiencies, we found that immature L. japonicus were euryhaline and at salinities ranged from 9 to 34 ppt showed similar feeding and growth rates. The suitable water temperature range was 22 to 28℃, and the optimal water temperature range was 26 to 28℃ for feeding and growth for immature L. japonicus.