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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
(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 33


                        BIENNIAL     REPORT                        33
  The fish having a large number of white and hard gill filaments were
found to be in very poor physical condition. There was no fat on the
intestine or body wall. The fish were lean and the muscles were firm. The
fish that had not been affected by the parasites showed the intestines sur-
rounded with fat and the body cavity was lined with a thin layer of fat.
The muscles had a firmness characteristic of fish in prime condition. This
observation has an economic bearing.
  It is a known fact that fish in nature put on extra amount of fat before
their spawning season. This reserve of fat is used up during the maturation
of the ova. Therefore, the number and quality of eggs produced by the
FOUR WALL-EYED PIKE. TOTAL WEIGHT 66H POUNDS. TAKEN
      FROM TOMAHAWK LAKE, ONEIDA COUNTY, WISCONSIN
individual fish is dependent upon its physical condition. The high death
rate of infected fish during or after the spawning season is no doubt due
to the weakened condition of the fish by the parasite. The constant
handling of the fish during this period is also a contributory cause as the
weaker fish are not able to withstand the stripping.
  The parasites are more numerous upon the old fish. A few parasites are
harmful to the fish. Even a single parasite withdraws from the trout just
enough blood for its own sustenance. The amount of blood required may
be small but it is a loss, and it weakens the fish by just so much, and if
the parasite dies this gill filament is functionless. When we consider that
there are found from 125 to 200 copepods on the gills of a single fish we
are forced to conclude that the drain on the fish's vitality is enormous.
With this constant drain there is no energy left for the production of eggs.
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