Shortly after salmon swim upstream to spawn, their bodies undergo a dramatic deterioration and the fish die within days. But, reasoned Donald L. Garling, a Michigan State University biologist, if the fish never felt the urge to spawn, they might just stay in deep water, growing bigger and meatier year after year.
Garling has found a way to eliminate the salmon's reproductive urge and, although the experiments are just beginning, he says his specially treated versions of Lake Michigan's Chinook salmon might grow beyond their usual 20- to 40-pound weight at maturity and become 60- or 70-pound leviathans in an additional three or four years.
Garling has created sterile salmon simply by placing salmon eggs in warm water, between 85 and 100 degrees Fahrenheit, for a few minutes. The eggs, adapted to cold water, are shocked by the heat and fail to undergo a normal developmental step. As a result, each egg contains a full set of paired chromosomes instead of the normal half-set that includes one from each pair.
Ordinarily the male salmon's sperm, bearing its own half-set of chromosomes, would fertilize a normal egg's half-set, producing a full paired set that would be the start of a new embryo. In Garling's hatchery, however, the normal sperm give the heat-shocked eggs a third half-set of chromosomes. The combination produces a fish normal in most respects except that it is unable to make viable sperm or eggs.
Its reproductive system disabled, this fish never feels the urge to swim upstream and keeps on growing, Garling hypothesizes.
Fingerling salmon produced this way last year are swimming in Garling's lab. They will be tagged and released into Lake Michigan next spring. Fishermen will be notified to send the tags to Garling, should they hook one of the special fish.
Because salmon normally spawn around age 3 or 4, it will be some time before Garling learns whether his fish have lived to be the lunkers to lure new anglers to the lake.