The relation between the construction of the trap for the Puffer fish and the fishing mechanism that it has was investigated. The relative efficiency of the trap was calculated with both the data of the trap width and the catch of fish. The calculated selectivity of the trap was compared with that es timated by the probability model for the Puffer trap fishery, taking into account the fish turning mo tion in a trap entrance. The obtained length selectivity for the puffer Lagocephalus wheeleri approxi mately agreed with the theoretical values. The length selectivity of the trap of the puffer Lagocepha lus gloveri showed higher values than the theoretical values. The selectivity of the trap calculated on the probability model seemed to be influenced by the length of the Puffer fish.We confirmed that the fishing mechanism of the trap for the Puffer fish depends on the behav iour of the fish inside of the trap entrance, but the behaviour of the fish seem not to be necessary uniform.
The ingress and escape behavior for a fish trap was studied through experiments in the laborato ry using green fish Girella punctata. The fish behavior for a simplified funnel set in the aquarium was recorded on video tape. An index of structure for various sizes of funnel-shape entrances was in troduced as a means of analyzing the entrapping difficulty. The following results were obtained: The number of fish entrapped was constant when the index was less than 1.0, but decreased when the in dex increased above 1.0, while the number of escaped fish decreased slightly as the index increased.
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