This paper described the effects of suction on fry sucked by the vacuum pump system which counts the number of seedlings fry with the sensor. The relation between suction pressure and suction velocity of the system was presented. Finally, drainage time of fry and water on the system was counted. The results were as follows. (1). When the lowest suction pressure was at 25kPa, so it didn't cause bad effect to the fry, the fastest suction velocity was at l.95m/s. (2). With the same suction pressure, the rate of fry injured was higher when fry was sucked from tail. (3). When the ratio of fish height to the inside suction tube diameter was over ０.46 (the ratio of fish length to the inside suction tube diameter was over 2.2), the fry would not be overtumed on the suction process.

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When the fry's numbers were counted with the suction counting system, a number of bubbles occurred. This paper describes the relation between the diameter of bubble and the light ray s power passed through the bubble. The smallest diameter of bubble detected with the light sensor was measured. In the case, the sensor's sensitivity was adjusted to the limit which the bubble could not be detected, the count accuracy of the fry sucked with the vacuum pump was also measured. The attenuation of the light ray s power passed through the bubble was theoretically analysed. The results are as follows. 1). When the diameter of bubble was big, the light ray s power passed through the bubble reduced. 2). Theoretically, in the case of neglecting the light ray s power attenuated by the air, the power passed through a bubble's center was reduced by 4%. 3). The smallest diameter of bubble which caused the calculation errors was equal to the smallest diameter which can be detected with the sensor. 4). When the sensor's sensitivity adjusted to below 9.7N, and the diameter of bubble is smaller than 4.6 mm, the bubble was undetected. When the ratio of fish height and measuring pipe's inner diameter is bigger than 0.6, all fry passing through the pipe was successfully counted.

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The tidal dam is a new technoIogical construction designed to improve the ecological environment of culture farm by providing oxygen to the oxygen-deficient sea water of the bay bottom in summer. There are three types of tidal dam ; One-Pipe-Type, Two-Pipe-Type (a), Two-Pipe-Type (b). The focus of this Study is experimentally and theoretically to find out a method of calculating the discharge of pipe-1ine in the Two- Pipe-Type (b) [TPT (b)] tidal dam among them. In this type tide dam, two pipes of different diameter were used. They were placed on the sane axis at some distance (⊿) from each other. TPT (b) doesn't need the gate for controlling water flow. At flood tide, the surface bay water flows into the reservoir through the upper pipe by its potential energy. At ebb tide, Water flows from the reservoir into the bottom of bay through two pipes. We here report a method to calculate discharge flowing through the two pipes. (1) The coefficient of energy loss (⊿f) occurring at the distance between two pipes, Which can be calculated by the equation (8), is in functional relation with their cross sectional area ratio (A2/A1), their distance ratio (⊿l/ D1) and Reynolds number (Re). (2) The discharge of TPT (b) can be calculated by the equations (9) and (10).

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Hydraulic properties are discussed of vortices separated at the edge of flat plate placed normally to the main flow in a water flow tank. Visualized experiments on separation vortices show that the spin down of vortex causes the upwelling of the bottom water. We develop a theory on the generation period of the separation vortex and the upwelling velocity, based upon the assumption that the kinetic energy loss of vortex due to spin down equals to the energy used to creat the upwelling, and by using the boundary layer theory and the mixing length theory on turbulent flow. Theoretical values of the circulation and generation period of vortex agreed well in good accuracy with measured values. No upwelling velocity is measured directly because of technical difficulty. Instead of the upwelling velocity, its volume is measured. We estimated the volume of upwelling by measuring the changes of dye concentration in the wake region behind the plate, since a part of bottom water in the wake is sucked up into the vortices and resulting in the decrease of dye concentration.

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A nursery aquaculture pond (1200m2 × 1.2m) for Japanese flounders, Paralichtys olivaceus, was constructed on a sandy beach. It utilizes wave energy for exchanging water in itself. To estimate how much inflow rate is needed to keep water qualities proper for flounders, a numerical model to forecast water quality was made. It consists of momentum equation, continuity equation and diffusion equations (water temperature, salinity, dissolved oxygen (DO)). The diffusion equation of water temperature includes the tem of heat flux depending on time through water surface・ The diffusion equation of DO includes the tem of consumption rates by suspended matter, sediment and respiration of flounders. However DO production is neglected. This model also can calculate the effect of coastal underground water upon the water quality in the pond. Heat flux was calculated by 'bulk' fomulas. DO consumption rate by suspended matter was measured by jn situ light and dark bottle oxygen method. That rate by sediment was measured in the similar method. That rate by flounders was calculated from the equation of expressing the relation between body weight and respiration rate. The quality of coastal underground water was measured on the spot and the quantity of that was estimated from the pumping tests. This model made it clear that the inflow rate of 227m3/hr is required to maintain the DO concentration over 3.0 ml/l all over the pond, and 313m3/hr is required to maintain it over 3.5ml/l. We could propose the useful method in deciding inflow rate in comection with water quality change.

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The authors manufactured experimentally rolling reduction device (hereinafter referred to 'ARS' : Antirolling System), and investigated motion reductions of a small fishing boat drifting in beam sea conditions. The summary of fact obtained from this investigation was as follows : 1) The spectra of roll angle and acceleration on Y-aXis in the boat with ARS were about 53% of that in the same boat without it. And the effect of motion reductions of experimental boat was shown in Fig. 14. 2) The double amplitude of roll angle, pitch angle and acceleration on X, Y, Z-axis could almost exactly be found by Reyleigh distribution even during ARS operation. 3) The balance-bag worked effectively on narrow frequency zone for the free rolling period of the boat. 4) The tension of the suspending wire rope was fluctuated greatly because an impulsive force was added to the boat with ARS. And the maximum tension was well applicable to Weibull distribution.

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The theory of directions control by the rotary feeder called the 'rotary direction-settler' has been evolved, for the purpose of developing the automatic arrangement system of catched fresh fish on a process to package them. The efficiency of the system has been estimated by the experimental equipment. Following results were obtained. (1) Judging from the theory and the experiment of relative position of the drum and the shoot, the system might use to the fish of similar body length whatever fish's species and weight. (2) It was found that the fish's direction is controled by the different of fish sliding velocity on shoot of headlong and backward. The efficiency of the system were rised by roughing the drum's surface. consequently, the rotary direction-settler might have enough efficiency for practical use.

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Behavioural features of artificially-bred juvenile red sea bream after stocking were reviewed. Several marking methods which have been used for stocking program were also evaluated by adopting the territorial behaviour as a behavioural index. The pigrnent injection method showed the least effect on their behaviours and was suggested to be the best marking method. After first stocking, three types of individuals showing distinct behaviours were distinguished : 1) territorial individuals, 2) territory-like individuals, 3) individuals keeping no restricted cruising area. Just after stocking, all fish were the type 3). Then, fish of the types l) and 2) increased in number gradually and became almost constant, which suggests that there exists a carrying capacity for the released population of red sea bream. However, the types 1) and 2) did not show a distinct increase in the second stocking. The differences in the recruitment pattem between the first and second stocking groups suggest that the effect of prior residence works, intermediated by the territorial behaviour.

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