Wisconsin. State Conservation Committee (1915-27) / Biennial report of the State Conservation Commission of Wisconsin for the years 1915 and 1916
Lowe, John N.
The effect of gasoline and benzine on the parasitic copepod, salmincola edwardsii olsson, parasitic on the gills of the brook trout, pp. 31-33 PDF (695.2 KB)
32 WISCONSIN CONSERVATION COMMISSION benzine. There was a spasmodic gasping for a while (3 to 40 or more minutes), when the fish would make an uncoordinated dash forward, the distance covered varying with the individual fish. The usual distance was from two to four feet, when they fell on their sides. After a rest of two or three minutes another start would be made. After this period of rest the fish would right themselves and swim about in a more or less coordinated manner and finally recover. Benzine was tried because it has a greater evaporating power than gasoline. It was found that fish treated with benzine recovered more rapidly than those treated with gasoline. The fish treated with gasoline, benzine, or a mixture of the two were apt to die after partial or complete recovery. The muscles in the tail region would begin to stiflen and slowly all the muscles of the body be- came involved. The heart continued to beat from three to four hours after the muscles of the body had stiffened. The parasites examined on a fish in this condition were found to be in a healthy condition, and continued to live for hours after the fish were dead. Most of the fish that were exposed to gasoline, benzine, or mixtures of the two, from one to five minutes recovered completely. The fish that died were individuals which were heavily parasitized or had been weakened by the parasites some time previously. There were a very few fish that lived after a six to ten minute exposure. In regard to the effect of gasoline and benzine on the copepod, it is clear from a study of the experiments listed, that the parasite can withstand the effects of gasoline and benzine for a longer period than any of the brook trout can, even those in the best condition. Very few brook trout can live in gasoline or benzine more than ten minutes, but the parasites live in them from seventeen to twenty-eight minutes. A few of the copepods die when exposed to gasoline or benzine from three to ten minutes, but the number affected is so small that for all practical purposes the results are negative. Careful examination of the parasites killed by gasoline or benzine showed them to be very young individuals or females that had shed their first or second batch of eggs. Probably the ruptured egg sacs permit the gasoline to penetrate into the vitals of the copepod. The vigorous females with their first egg sacs developing are not killed by gasoline or benzine. The life cycle of the female copepod is about three months. After this period death ensues and the dead parasite and the affected gill undergo deterioration. This reduces the number of functioning gill filaments, and the respiratory functions of the fish. The dead copepod and the affected gill filament serve as a locus for bacterial and fungus infections. Many of the fish examined had no paraistes on their gills, but from the white color of the degenerated gill filaments showed conclusively that they had been heavily infected. It was fish in this condition that died first, even a three minute exposure to gasoline or benzine causing death. The affected gill filament appears white in color and is very firm to touch. This hardness is probably due to the formation of the scar tissue. The whiteness of the gill filaments is caused by the destruction of the very fine capillaries of the gill filaments. With this impoverished circulation and respiration the vitality of the fish is very much reduced.
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