Tailwater Trout


Tailwater trout are stupid, and because of consistency in their environment are becoming more stupider every day.

This is one potential conclusion from the work of researchers from the University of Bern, Switzerland in work published in the online scientific journal PLOS One. In a paper titled "Environmental Change Enhances Cognitive Abilities in Fish" authors Alexander Kotrschal and Barbara Taborsky stated when the cichlid fish Simochromis pleurospilus was subjected to variation in dietary availability early in life -- either reduced or increased -- the fish exhibited enhanced cognitive abilities over the course of individual otogeny, or, the development of an organism over it's lifetime . While the study was conducted on a different species, the finding potentially implies that trout reared in highly variable Freestone biologies could have an enhanced rate of learning and survival skills as compared to fish living in relatively stable Tailwater environments.

As quoted from the text of the study, "On the level of the individual, environmental instability can be encountered by plastic trajectories of the development of cognitive abilities. Environmental fluctuations early in life are known to enhance the behavioral flexibility of animals with regard to predator avoidance strategies [6],[7], feeding performance [7], and social behavior [6],[8]. A possible explanation for these behavioral effects is that variable environments evoke repeated neural stimulations resulting in faster and better learning."

(Photo via Facebook/anglerscovey)

Fish were fed either on a stable high or a stable low food ration, or rations were switched from low to high or vice versa. They then trained the fish to associate a visual cue with food and tested how often they selected the positive stimulus. Fish that had more variability in their food availability early in their lives showed increased ability to make correct associations with abstract stimuli and food.

Natural Freestone stream biologies are highly unstable in regard to a  number of factors that affect food type and availability.  Water temperature, volume, turbidity, and wide variety of insect species all contribute to a dynamic and demanding environment where trout are challenged to survive daily.  In contrast, while rich in regards to overall biomass, Tailwater fisheries tend to be relatively stable in terms of temperature and water clarity owing to the thermal mass and sedimentary settling of the reservoirs above the dams which provide prime trout growth habitat in their outflows.  This typically results in large volumes of only a few types of food forms such as midges, smaller crustaceans like scuds and shrimp, and aquatic terrestrials like sowbugs and worms being available year 'round.

Photo courtesy Bob Streb

Most experienced tailwater anglers will agree that only subtle pattern changes and a completely drag free presentation are crucial in success with trout living below dams, but that in general, these fish are very tolerant of crowding and angler proximity, preferring to focus on easy feeding positioning in areas of prime insect drift, and rejecting food forms out of the norm.  In contrast, wild fish living in small headwaters and tributaries tend to be spooky in the extreme when approached by fisherman, but also quite opportunistic when presented with fly patterns that are out of the current norm.  The study cited above would indicate that the differences in variability of the two environments are responsible for programming the fishes orientation towards learning and adaptability, and not just species.

There could a takeaway for humans here. People who have been exposed to environmental variability like outdoor sports or adventuresome culinary experiences early in their lives may gain a neurocognitive advantage towards learning or adaptability.  Those who spend most of their lives as video obsessed couch potatoes eating pork cracklins may become incapable of change or interpretive thought. Any potential societal or political inferences from this hypothesis would be wild conjecture, however, and should not be be interpreted as an official position of this publication.

It would appear that wild rivers may breed free thinking fish, while trout that spend their lives staring at gigantic concrete rectangles just get dumber!

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