From Newsgroup: talk.origins
On 7/26/2026 2:09 PM, Ernest Major wrote:
Another transmissible cancer discovered, this one infecting Ameiurus nebulosus (a catfish). It's not the 4th discovered, but that claim goes
back to the paper in Nature, which overlooks contagious reticulum cell sarcoma of Syrian hamsters, and counts the various reports from bivalves
as a single instance.
https://www.forbes.com/sites/johndrake/2026/07/24/scientists-discover- the-fourth-transmissible-cancer-known-to-science/
https://www.nature.com/articles/s41586-026-10828-6
This transmissible cancer is different among vertebrates in that it can
infect genetically dissimilar catfish of the same species. They need to
check to see if that lake had selection for a limited number of alleles
at their MHC locus. This is the locus that is involved in telling self
from nonself antigens. In birds the number of class I genes is limited
and different alleles have differential resistance to specific
pathogens, so single populations subjected to a heavy disease load of a particular pathogen could select for a single allele in that lake. All
the fish may be tissue compatible.
Googles take on MHC in fish:
QUOTE:
MHC Systems in Fish
Presence: Most jawed fish possess both MHC Class I and MHC Class II
molecules that manage adaptive immunity.
Genomic layout: Unlike mammals, teleost (bony) fish often have their
classical MHC Class I and Class II genes located on separate chromosomes rather than tightly linked together.
Exceptions: Certain fish groups, such as Atlantic cod and pipefish, have completely lost the MHC Class II pathway during evolution, relying on alternative immune strategies instead.
Tissue Compatibility and Rejection
Transplant rejection: Research using scale and skin grafts on fish (such
as the Gila topminnow) demonstrates clear acute and chronic tissue
rejection.
Allele matching: The success of tissue grafts between fish depends
heavily on how many MHC alleles the donor and recipient share, mimicking
the mammalian rejection response.
END QUOTE:
For Tasmanian devils the cancer is tranferred by biting. The population
went through a severe bottleneck and from what I have seen, inbred
individuals are tissue compatible, so the cancer can spread through the population and isn't rejected.
Ron Okimoto
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