This paper describes the reactions of freshwater fishes to He-Ne laser light and discuss herding effect of moving laser screen. The indoor tank experiments were conducted to examine herding effect at different fish numbers (10, 20 and 30 fish) and different species (Japanese dace Tribolodon hafronensis, carp Cyprinus carpio and rainbow trout Oncorhynchus mykiss). In outdoor tank, it was attempted to herd rainbow trout at different moving speeds of laser screen. Laser temporally dispersed fish school, and then fish again swam in school avoiding the laser. Thereby laser can drive fish into an area of tank. Fish are however considered to leam to escape through laser screen, since herding effects decreased, following repeated exposure to the stimuli of laser screen. Laser could herd fish more effectively in the dark than in the light at the indoor tank experiment. The larger fish number of Japanese dace was, the sooner laser screen could herd. Moreover, the herding effect was different among species. The proportion of herded rainbow trout decreased over 25 cm/s of laser screen moving speed. It is therefore resulted.that the herding effect depends on several factors e. g. fish school behavior and swimming performance.

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To aim for the automatic arrangement of catched fresh fish on a line pior to packaging them, the motion of the vibratory plate and the movement of fish on the vibratory feeder called the 'vibratory direction settler' here have been studied. Following results were obtained. (1) It was found that fish is conveyed headlong by inertia force of fish and difference in friction force acting on fish between headlong and backward. (2) A vibratory plate with resinous sheets conveys fish more quickly than one with metallic sheets owing to its greater friction. For fish with fragile skin it should be noted that a rough resinous surface might injure them. (3) The rapid retum motion of the vibratory direction-settler consisting of a crank chain, two coiled springs and four plate springs contributes to quick transmission of fish. (4) The saury-processing efficiencies of vibratory direction-settler were 2.0 ton per hour with the metallic surface of the vibratory plate, and 2.4 ton per hour with the resinous surface. Consequently, the vibratory direction-settler might have enough efficiency for practical use.

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A numerical simulation on the dispersion of swimming crab (Portunus trituberculatus MEIRS) megaropae is carried out in Hiuchi-Nada, the central part of the Seto Inland Sea. The calculated dispersal pattem of megaropae in the 3-dimensional numerical model well reproduces the observed one. The vertical migration of swimming crab megaropae plays an important role in their retum process from offshore to the nearshore region.

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The idea of the tidal dam is proposed to prevent the oxygen deficiency in the bottom layer of a themally stratified water in an enclosed bay. Ejecting the solar heated reservoir water into the sea bottom, a vertical water circulation may be generated in a highly stagnant water only by the tidal potential energy. In this study, the hydraulic feature of flows in pipes which connects the dam reservoir and the sea, is theoretically and experimentally examined to estimate the volume of total waters ejecting from the dam reservoir into the sea during one tidal cycle. Although the water flow driven by the tidal motion in this system is unsteady, the kinematic proper period of the pipe flow is considerably shorter than the tidal period. Therefore, the phenomenon which we concem here, can be practically regarded as a steady one. Neglecting the time varying inertia term in the goveming equations, the ratio of the tidal range, A in the dam reservoir to that of the sea can be represented as a function of the following parameter : where F is the energy loss coeffcient in the pipe system, ΔhB is the half of the tidal range in the sea, ω (= 2 π/T) is the angular velocity of the tidal fluctuation, T is the tidal period, g is the gravitational acceleration, SD is the area of the dam reservoir and A is the cross sectional area of a pipe. The functional relationship is verified through hydraulic model experiments.

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The laboratory and the field experiments was conducted by using of carboxylic acids (malic and citric acids) for artificial formation of seaweed Sargassum ptens bed. In the laboratory experiment, both malic and citric acids were confirmed to promote the growth of germlings and fronds of S. patens in the culture. In the field experiment, the experimental substratum was prepared using a plastic plate (200×200mm in size, 10mm in thickness) coated the resin containing the respective carboxylic acid. Each of the plates was sowed with about l,000 germlings and soaked in the experimental ground at 2m in depth. S. patens on the malic acid plates highly showed good growth for 8 months and many fronds survived on the plates. Meanwhile the growth of S. patens on the citric acid plates was low and inferior to the effect of the malic acid plates. The fronds of S. patens on the plates non-treated became extinct in 4 months. The field observations showed that malic acid was a nourishing source for the growth of S. patens and also prevented benthic animals from grazing in seaweed bed. A beneficial effect on formation of seaweed bed can be expected by utilization of malic acid.

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Laboratory experiment was carried out to know the function of artificial reefs as a protector of small prey fish against predators. Time sequence of survival rate of prey fish were examined in 6 different sets of predator-prey combination. Depending upon 32 observations, SurVival rate in prey fish increased due to the presence of reefs, especially the reefs of more complex structure. The survival rate of prey fish varied with the reef-affinity in both prey and predator fish and also with the feeding behavior of predator fish. Higher survival rate was observed in prey fish that have higher reef-affinity. These results suggest that artificial reefs play an imporant role in creation of nursery through their function protecting smaller prey fish against larger predator fish.

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The mechanism of schooling behavior of fish has been studied mainly from the ecoIogical viewpoint. With the development of marine ranching, this subject becomes more important both for fishery resource management and for controlof fish behavior. In this report, We consider the mechanism of fish behavior from another viewpoint, i.e., system engineering approach. In system engineering, modeling and simulation techniques are used for analysis, design and plaming of not only technical but also non-technical systems. The result obtained by computer simulation may be expected to give us a new suggestion for considering the problem. This report deals with a fish school as an autonomous decentralized system, which is one of recent interesting subjects in system engineering. A water tank experiment is carried out to obtain an observation data for fish behavior and to know a special feature of school. The unknown parameters included in the model are estimated by using a water tank experiment data. The relationship between the autonomous decentralized mechanism and fish behavior is investigated from simulation results.

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A background information on swarming response of fish to artificial reef, reef-afinity, is presented to develop a reef technique as one of the methods for controlling fish bahavior. Nature and magnitude of the reef-afinity is variable according to fish species, its developmental stages and physiological conditions. In some fish species, the reef-afinity is emphasized along with growth of fish. Some fish are attracted not only reefs directly but also small living organisms gathering around reefs. For controlling fish behavior, the artificial reef techniques should be employed according to the specific function of reef, such as spawning area, shelter and resting place of fish.

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