This paper describes the diel periodicity of feeding activities and stomach contents compositions of two young flounders, Pleuronichthys cornutus and Pleuronectes yokohamae which show a sympatric distribution in Suo-nada, western Seto Inland Sea. Sampling by a small trawl net was conducted 11 times over a period of 24 hours during 7 and 8, July, 1984. The number of caught flounders, P. cornutus and P, yokohamae were 463 (Body length, 50∼110 mm) and 602 (Body length, 30∼90 mm), respectively. Both species showed a similar die! feeding activity. The stomach contents weight index (SCI=stomach contents weight×10²/body weight) increased from early morning to about sunset. After sunset, the SCI began to decrease and reached the minimum before sunrise. The highest SCI of P. cornutus was approximately 1.5, which was three times larger than that (nearly 0.5) of P, yokohamae. Moreover, the percentage of fish with empty stomach was high just before sunrise and became very low during daytime. These results show both species feed on prey chiefly from early morning to evening. The stomach contents of P. cornutus and P. yokohamae consisted mostly of small size polychaetes, Paraprionospio sp. (Type B) and Lumbrineris sp., respectively, both of which were dominant in the macrobenthic fauna in Suo-nada. The continuous observations on the stomach contents of both flounders clearly showed that Paraprionospio sp. (Type B) tends to be digested more easily than Lumbrineris sp. This fact strongly suggests that P, cornutus has an advantage on the feeding strategy over the sympatric counterpart.

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A new sampling method and a new in situ rearing method are described for caprellid amphipods and other epiphytic animals on Sargassum thalli. A plastic bag with a drain-hole covered with nylon mesh was found to be efficient for underwater sampling of epiphytic animals. The sampling bag is easy to assemble or reassemble, facilitating fixation and handling of the animals in the laboratory after sampling. For the in situ rearing experiment, caprellids on Sargassum were put into a transpar-ent plastic container, of which the top and bottom surfaces were covered with 250um nylon mesh. The containers were set in a plastic basket and then suspended 3.5 m below the water surface. There was no need to feed the animals in this rearing system. The 250μm nylon mesh of the container never permitted entry of other caprellids ; moreover, the pores of the mesh were slow to clog and required little maintenance. Cleaning was needed only every 7 to 10 days because the rearing system, which was suspended near the water surface, allowed water to pass continuously through the containers.

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Annual changes in density and community types of the macroinvertebrates inhabiting the extensive mud and sandy mud bottoms in Mutsu Bay, Aomori Prefecture were studied on the basis of summer samples obtained during 1979-1988 (except for 1984). Although two samplers, Tamura grab and Smith - McIntyre grab, were used at the mud and sandy mud stations, their relative efficiencies were similar in terms of the numbers of collected individuals, the species richness, and species composition. Mud and sandy mud bottoms in the bay were consistently dominated by polychaetes, accounting for 71∼93% of the total number of individuals. Remarkable annual fluctuations in abundance were observed for several main polychaetes. However, the total abundance of macrofauna in the bay was relatively stable, because species with high density occurred successively. From year to year, the types of macrofaunal community changed dramatically with variations in abundance and spatial distribution of the main polychaetes. In general, when habitats of dominant species overlapped, the density of one of these species reduced markedly in the following year. These facts suggest the possibility that the competitive interaction between the same trophic organisms affects the abundance of the main polychaetes and the community structure within this study area.

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Methods for preparations of mitotic chromosomes are described for use on polychaetes. Well-spread metaphases are available by using larvae (trochophores, metatrochophores and nectochaetes) and adult tissues (clumps of spermatogonia and regenerating posterior ends). Principal procedures of the preparations consist of the following steps : 1) Pretreatment of the materials with a 0.005-0.05% colchicine solution. 2) Immersion in a hypotonic solution (1% sodium citrate). 3) Fixation in a freshly prepared fixative of methanol-acetic acid (1:1 or 3: 1). 4) Spreading of cells on a glass slide. 5) Air-drying or flame-drying. 6) Staining with a 2 % solution of Giemsa.

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Specimens of the freshwater crab Geothelphusa dehaani (WHITE) were collected at 60 points of Kagoshima Prefecture to study the color variations appeared on the carapace, cheliped, and am-bulatory legs from May to September of 1989. The color variations were fundamentally distin-guished into three types : Blue Type, Red Type, and Brown Type. The color of young crabs were Brown Type and changed into Blue Type or Red Type when the crabs reached more than 14mm in carapace width. Red Type crabs were distributed to the north of Kamino River, Satsuma Peninsula and Kimotsuki River, Oosumi Peninsula, while Blue Type crabs were distributed to the south of these rivers. The predominant carotenoids were lutein, astaxanthin, astaxanthin diester, and astaxanthin monoester in the Red Type crabs, while in the Blue Type crabs they were β-carotene and lutein.

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Molt and survival of the penaeid shrimp Trachypenaeus curvirostris (carapace length: 10.5-24.0 mm) were studied at the temperatures of 10, 12, 15 and 22°C. All or most shrimps died without molting at 10°C, and after molting at 12°C. These mortalities at low temperatures were low on the larger individuals, and hardly differed between the male and female. The shrimp examined at 15 and 22°C molted more than once during rearing of 68-90 days, where the larger individuals tended to have longer intermolt period and smaller molt increment. The intermolt periods of the female at 15°C ranged from 24 to 57 days, which were 2.3 times longer than those at 22°C, whereas no significant difference was seen in the molt increment (0.9-9.3%) between both temperatures. The growth rate estimated in the present study well explained the growth of natural populations.

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