So, what is a tiger trout, and why are they so rare?
Tiger trout are the result of a wide cross or hybridization between two different species - the brook and the brown trout. Making this cross even more unique is the fact that brook and brown trout each belong in a separate genus - Salvelinus for brook trout and Salmo for browns. lthough this cross can easily be performed by a fisheries biologist or a curious hatchery technician, it is rare in the wild. Experiments performed at the Benner Springs Research Station during the 1950s found that even in the controlled conditions of a hatchery, only about four to five percent of the fertilized eggs survived to the fry stage. The state of Wisconsin, more recently, has had survival rates as high as 25%. Some private breeders have done a little better, but the survival rate never approaches the normal rate of brook or brown trout.
According to Bill Willers in Trout Biology, this type of cross is most successful (and sometimes only successful) if the female species has the larger eggs and the shorter incubation period. With tiger trout, the female must be a brown and the male a brook trout. The body shape of a wild tiger trout is most like a male native brook trout, while their scales are larger, like those on a brown trout. A tiger trout's spotting pattern is considerably different from either parent and, as you can see from the photograph, quite striking. The normal vermiculations of a male brook trout seem to be enlarged and contorted into stripes (hence the "tiger" moniker), swirls, spots, and rings. Every one that I've seen also has a greenish cast, which lets you know that there is something different on the end of your line long before the fish is in hand.
Although tiger trout look like males, they are sterile. Charles Krueger, from Cornell University, states in the book, Trout, that the "infertility of the tiger trout may be caused by the dissimilarity between the chromosome numbers of the two parent species." Brook trout have 84 chromosomes and browns have 80.
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For more information and the complete story, go to:
http://www.patrout.org/tiger.htm
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