An Experimental Study of the Movements of Herring and Other Marine Fishes

We note that on the whole the presence of a quantity of carbon dioxide in the water affected the fishes less than a smaller amount of hydrogen sulfide. The combination of hydrogen sulfide and carbon dioxide was most rapidly fatal. Since decomposition yields CO2 and consumes oxygen and is accompanied by the production of hydrogen sulfide which is also accompanied by the consumption of oxygen, it is reasonable to suppose that on a bottom from which vegetation is absent and decomposition actively takes place a fatal combination of lack of oxygen, and presence of hydrogen sulfide and probably carbon dioxide can develop quickly. Considering the fishes tested we note that the herrings were most sensitive. They were sharply marked off from the bottom species which are resistant to a marked degree. This resistance is in a very general way associated with the habitat preference of the species. Still the marked resistance of the small cottid is not quite explicable on this or any other basis. The importance of factors which kill fishes is greatest in the early stages for two reasons. First the small size of the eggs and embryos makes the ratio between volume and surface smallest and thus any substance in solution will reach all parts of the organism at a more rapid rate. Secondly the inability of the eggs and embryos to move about makes them the easy victims of any adverse conditions that may occur. The eggs of the herring are deposited on the bottom. Nelson mentions rocks only (Marsh and Cobb, `10, p. 46) and rocks are usually swept fairly clear of organic matter and the water well aërated down to the depth of one fathom where the fishes breed. If this means that sandy bottoms of bays are avoided it probably means the avoidance, during the breeding, of water high in hydrogen sulfide (see table) which would be fatal to the eggs and small herring fry to a greater degree than to those studied, which were 6 cm. long. Sensitiveness to hydrogen sulfide is a matter of much importance from the standpoint of the suitability of a given arm of the sea for herring and the influence upon fishes of contamination of the shores with refuse from the land. Carbon dioxide is not high in such shallow water on account of the presence of so many green plants. Carbon dioxide is probably more important in connection with movements of the fishes than in the matter of restricting their breeding places.