However, ruled out as a cause is radiation seeping from the nearby Hanford Nuclear Reservation. The amount of radioactivity known to be going into the river is too small to have produced such changes, according to the study's authors. The study by Nagler, Gary Thorgaard, a fish geneticist at Washington State University, and two other researchers, was published last week in Environmental Health Perspective, a journal of the National Institute of Environmental Sciences. Most of the female fish carried a genetic marker found only in male salmon. This could be a contributing factor, coupled with all the other burdens on the backs of these fish, that tweaks the health of these populations.
Sex determination is more relaxed in fish than in humans or other animals.
Nagler said the sex of salmon has been changed under laboratory conditions, usually through the concentrated use of hormones. For example, aquaculture farms sometimes transform male salmon into females because the females often grow larger and produce more desirable meat. But the phenomenon has never been seen in wild salmon stocks, according to Nagler and other researchers. Indeed, this may already have happened, the researchers conceded. Normally, female fish carry two X chromosomes, while males carry an X and a Y chromosome.