On Fouling Organisms in the Oyster Farm

Abstract

In recent years a method of oyster culture, i. e., the so-called raft- or hanging-method has become popular all over the coast of Japan. In the said method, as the name signifies, clusters of oysters to be cultured are hung and suspended in the sea by steel wire from the raft which is kept buoyant by some floats. While thus the oyster clusters are relaid in the sea, many kinds of sessile organisms settle and grow on the living oyster shell often as densely as they almost cover up the whole surface of the shell-flish. The condition that the oysters are continuously immersed in the water, not being given the chance of exposure to the air even in the receding tide is the chief cause of the fouling. The fouling organisms stand undoubtedly as food rivals to the oyster, because many of them are plankton feeders, and so it is quite certain that the fouling brings about the retardation of the growth of the oyster to some extent. Not only that, some organisms, such as compound ascidians and others encrust the shell surface as they grow and often almost choke the oyster. The oyster thus comes under the deleterious effect in many ways by the fouling. And moreover, the fouling organisms are a great nuisance to the oyster farm. When the season comes and the oysters are collected for marketing, it is the most tedious work to clean off the fouling organisms from the oysters. In some cases when the growth of the fouling organism is very heavy, the collected mass of the oyster s consists in greater part of fouling organisms, not of the oysters themselves. Such cases are not quite rare. Nevertheless, by virtue of the rich fouling the oyster culture farm of the raft-method makes good fishing place for edible fishes, as many of them gather under and around the raft where the oysters are suspended in the sea. The oyster clusters overgrown by fouling organisms give the fish its gool sheltering place on one hand and plenty supply of its food on the other. © 1938, The Japanese Society of Fisheries Science. All rights reserved.