One of the questions arising
from studies of seasonal incidence of walleye dermal sarcoma
was whether a fish that was tumor-positive in a given year would
again be tumor-positive in the following year. An investigation
is underway to answer this question but the nature of the environment
has required an indirect approach. The reason for this approach
are as follows:
In any given spring, one can
expect that approximately 20% of the adult walleyes brought to
the Oneida Fish Hathery will be tumor-positive for WDS. In terms
of numbers, this means that (approximately) 8,000 of the (approximately)
40,000 adult fish will be tumor positive. This is out of population
of approximately 300,000 adult walleyes in Oneida Lake. If all
8,000 tumor-positive walleyes are tagged during the spring spawning
run and are released into the lake, the chances of recapture
of a tagged fish is 2.67% (8,000/300,000). The conclusion was
that the direct approach of a mark and recapture study was not
likely to be a productive effort.
The indirect approach consisted
of a cooperative effort with the staff of the Cornell University
Biological Field Station (CUBFS) on Oneida Lake. For several
years, beginning in 1995, tumor prevalence data was collected
as part of the walleye growth and life history studies of CUBFS.
During the spawing run approximately 500 male and 500 female
walleye were examined. Data collected included: sex, total length,
age (scored from scales) and presence of walleye dermal sarcoma.
The approach is to follow the various year classes of walleyes
as they increase in age from each year to the next. If a walleye
is tumor-positive in a given year and is again tumor-positive
in the following year(s), one would expect tumor prevalence to
be higher in older age classes. A preliminary examination of
the data would suggest that this is not the case. An in-depth
analysis of the data will be performed following collection of
the 1999 data.
References:
Bowser, P.R., M.J. Wolfe, J.L. Forney, and G.A. Wooster.
1988. Seasonal prevalence of skin tumors from walleye (Stizostedionvitreum) from Oneida Lake, New York. J. Wildl. Dis. 24:292-298.
Getchell, R.G., J.W. Casey and P.R. Bowser. 1998. The seasonal
occurrence of virally-induced skin tumors in wild fish. Journal
of Aquatic Animal Health 10:191-201.
