Pêche sans -filet et théorie des tropismes

Recent ideas about fishing without a net have still not given way to a large practical application, but they bring back a theoretical question currently left alone: the question of tropisms. This question emerges from the evolution of the conceptions which led to these futuristic views from traditional methods, and that we are going to briefly consider.In cast net fishing, the fishing device goes to the fish: one wants it to stay still. Gillnet fishing on the contrary works with the mobility of the fish, which throws itself in the trap, if it has been positioned in the right way.A great improvement is the combined use of ring net and salted cod-roe, as the mobility of the fish is guided by the bait: there is a food attraction and thus a fish gathering enabling the sweep. The catch operates in two phases: the first phase is attractive, through a chimiotropism effect in a gradient of dissolved substances, and the second phase is coercive, as were the previous cast net and gillnet techniques.This duality can be found in recent trials combining the effects of light and of a pump (NIKONOROV and PATEEV, 1963). Here again, we find an attraction (phototropism) in the first place, then a coercition (water pumping). The addition of an electrical stimulus has been tried recently (KREUTZER, 1958) and these attempts tried to answer some problems of practical efficiency, for which the solution is based on the theoretical principles we are going to consider.