Part 2: Survival Traits of Rainbow Trout
© Jeramie Tesky and Diana Tesky
Most sources will refer to what we are calling “survival traits” as “adaptations”. Given that the definition of an adaptation is any "Feature of structure and function that suit an organism to the conditions of its environment" (Ricklefs 1993), “survival traits” use as a replacement term serves to sum up the meaning of the word without adding the connotations that adaptation can carry. Speaking of adaptation/survival traits in the framework of populations, the definition might read: features that suit a population to its environment. In other words, anything that promotes the survival and continuance of a population and further generations of that population could be an adaptation/survival trait.
Rainbow trout need several specific traits to survive the conditions they live in. Where one condition favorable to the rainbow exists, another may be unfavorable, harmful, or even lethal. For example, clear, cool water streams may not have the food adequate to support a rainbow population, or in areas with food, the water quality may not be as good. In almost any area rainbows are found, there is a trade off of some sort or another. It's unlikely that any rainbow population will live in an absolutely ideal or "Perfect" habitat. For this reason, we can study how a rainbow population is suited for the various conditions. We can observe how the trout population will respond and change behavior to better survive. In essence, we can see these survival traits in action by observation of how the trout put the traits to use in differing circumstances. One situation a trout population might encounter is high water temperatures. Above normal temperatures can slow growth in a rainbow, and temperatures > 25 degrees Celsius are lethal (Matthews et al. 1997). If water temperatures do not kill the fish, their growth rate will still be slowed. Fish with slower somatic growth will be smaller at maturity. Fecundity is directly related to body size (Hines 1976), so fewer eggs will be produced by the population in warmer waters. This, over time, will cause the population to dwindle in size. The rainbow population has to have some way to deal with the warmer temperatures to ensure its continuance.
According to a study conducted by Lynn Kaeding in 1996, one way that rainbow trout can deal with areas of warmer than tolerable water temperatures is to move to cooler temperature waters. Kaeding’s study was conducted in the Firehole River, and two tributaries in Yellowstone National Park, Wyoming. The Firehole River has heated water from hot springs and geysers flowing into it, while the tributaries (Sentinal Creek and Little Firehole River) are solely cool water streams (Keading 1996).
