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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)

Page 32

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
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
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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