Experimental Transmission and Age of Fish
and Route of Challenge
The laboratory-based transmission
model was used to investigate the effect of age experimental
transmission of walleye dermal sarcoma. All previous transmission
trials had been performed with 12-week old fish. The experimental
design encorporated the use of 6-, 8-, 12-week-old, and 1 year-old
fish. Walleye dermal sarcoma became invasive in fish challenged
at 6- and 8-weeks of age. This was the first known malignant
behavior of walleye dermal sarcoma. In all previous investigations
with feral fish and in laboratory experiments, walleye dermal
sarcoma remained superficial in nature and was considered to
be a benign neoplasm.
It is likely that transmission
in feral populations occurs by a topical route of exposure. During
the spring spawning run, large numbers of walleyes, with as many
a 20-30% being tumor-positive, congregate on shoals or in streams.
Such crowding facilitates exposure of walleyes to walleye dermal
sarcoma virus that may be free in the water. Initial efforts
to investigate such a route of exposure consisted of preparing
cell-free tumor filtrates and exposing fish via the topical route,
oral route and intramuscular route. In all three cases, transmission
was successful.
References:
Earnest-Koons, K., G.A. Wooster and P.R. Bowser. 1996. Invasive
walleye dermal sarcoma in laboratory-maintained walleyes (Stizostedionvitreum). Diseases of Aquatic Organisms 24:227- 232.
Bowser, P.R., G.A. Wooster, and K. Earnest-Koons. 1997. Effects
of fish age and challenge route in experimental transmission
of walleye dermal sarcoma in walleyes by cell-free tumor filtrates.
Journal of Aquatic Animal Health 9:274-278.
