A while back, I had the opportunity to see some cool pictures of tiger trout caught in Vermont by Maine resident Sean McAuley.  McAuley did what very few fishermen have the opportunity to do: he caught multiple tiger trout that occurred naturally in the wild.  He also took some great pictures of the fish and gave me the opportunity to post them here.

The tiger trout (Salmo trutta x Salvelinus fontinalis) is a sterile hybrid cross between brown trout and brook trout, and is very rarely seen in the wild.  Instead of looking like a typical hybrid with some coloration characteristics from each of its parents, the tiger trout looks completely unique.  It doesn’t just have the distinguishing spots and parr marks that other trout have.  True to its name, the tiger trout has extensive vermiculations along its sides that somewhat resemble the stripes of a tiger.   

It is believed that the cross between the two trout species results when a male brook trout fertilizes the eggs of a female brown trout.  While they spawn around the same time, brook trout and brown trout usually segregate during spawning, and do not share the same type of microhabitat for laying their eggs.  It is believed that brook trout typically tend to seek groundwater inputs for spawning while brown trout simply target suitable gravel.  Research has shown that brown trout and brook trout spawning redds seldom overlap, but in some cases they do spawn together, and tiger trout are documented in the wild from time to time. 

One of the reasons that the tiger trout is so rare is that the two species forming this hybrid are each in a separete genus, and have different numbers of chromosomes.  In other words, they aren’t as closely related as many other species that hybridize.  Brook trout have 84 chromosomes, while brown trout have 80. 

Tiger trout have become a popular tool for fisheries managers in a number of states, where they are bred and raised in hatcheries and stocked in lakes or reservoirs to provide a unique sportfishing opportunity.  Fish culturists have been successful in breeding tiger trout by heat shocking brown trout eggs, which adds an extra set of chromosomes and greatly increases survival rates.  Survival rates from fertilization in the wild are very low.

Because it is so rare in the wild, hybridization between native brook trout and introduced brown trout has not often been discussed as a threat to brook trout populations, while competition and predation by brown trout are believed to pose a more significant threat to native fish.  The tiger trout is truly a unique fish, only found in rare instances where brown trout and brook trout coexist, and I envy anyone fortunate enough to have the opportunity to land one!