Adventursome Personalities in Trout

https://www.youtube.com/watch?v=K23-ZuA9EX8

According to a recently released study, scientists at Exeter University in England have determined that Guppies have distinct individual personalities. The fish's reactions to various situations and stresses indicated unique coping strategies that can be attributed to individualized cognitive profiles. Parallel university research has correlated the stream movements of Brown Trout to biochemical data in the fish's blood, and appear to have implications for trout anglers wanting to better understand their quarry as well.

Coverage from Timeslive provided the following,

"Scientists from Exeter University in southwest England studied how individual Trinidadian guppy fish behaved in various stressful situations and discovered wide differences in how they responded. The researchers studied their coping strategies in situations designed to trigger various levels of stress. They found their modes of behavior could not simply be explained as risk-taking or risk-averse."

"When placed into an unfamiliar environment, we found guppies have various strategies for coping with this stressful situation - many attempt to hide, others try to escape, some explore cautiously," said Tom Houslay, of the university's Centre for Ecology and Conservation.

"The differences between them were consistent over time and in different situations. So, while the behavior of all the guppies changed depending on the situation - for example, all becoming more cautious in more stressful situations - the relative differences between individuals remained intact. The tiny guppies were individually transferred to an unfamiliar tank, to create a mild level of stress, while a higher level of stress was caused by adding models of predatory birds or fish."

While Guppies are not generally considered of interest to fly fishermen, the insight gained from the research may now potentially be extrapolated to trout. A study released within the same news cycle as the Exeter work from the Institute of Biomedical Research at the University of Lleida in Spain has shown that blood chemistry in Brown Trout--analyzed through the new science of metabolomics -- indicates that individual fish can be more inclined to search out new territory or engage in localized migration than others that are inclined to a sedentary lifestyle.

According to the study abstract by lead author Neus Oromi,

---

"The mechanisms that can contribute in the fish movement strategies and the associated behavior can be complex and related to the physiology, genetic and ecology of each species. In the case of the brown trout (Salmo trutta), in recent research works, individual differences in mobility have been observed in a population living in a high mountain river reach (Pyrenees, NE Spain). The population is mostly sedentary but a small percentage of individuals exhibit a mobile behavior, mainly upstream movements. Metabolomics can reflect changes in the physiological process and can determine different profiles depending on behavior."

The summary of the research concludes that, "The metabolite profiles differentiated the individuals according to the home range classification (sedentary and mobile) and showed different level concentrations of some metabolites, which interact in different pathways. Considering that stream-resident S. trutta in the Flamisell river is mainly sedentary, the small proportion of individuals with mobile behavior, clearly differentiated by the metabolic profiles, can have a relevant function in the population dynamic."

What the heck does this all mean, anyway? In the case of Salmo Trutta, it is interesting as Brown Trout are famously territorial, defending home pools and preferring calmer, predatory lies than other species of trout such as Rainbows. The metabolomics analysis of the Spanish Browns indicates that typically, these sedentary trout will have a home range of not more than 800 meters within a stream, engaging in seasonal forays of only an extra 100 meters to find appropriate spawning beds. During the spawn, salmonids like trout exhibit large increases in hormones that can manifest in physical changes such as development of jaw kypes and more vivid coloration in males.

However, the study made analysis of individual fish that had made broader movements outside of spawning season. The results found that these fish had measurably different levels of metabolic markers such as the stress hormone cortisol, indicating that they may be uniquely more intolerant of pressures being experienced within their home range, such as increased incidence of the presence of fishermen. They just aren't putting up with it.

As every angler knows, large, old fish are smart -- they don't get to be that way by making rash decisions or allowing harassment. If some individual trout that are by nature inclined to seek out more remote or difficult sections of river to elude human predators are genetically predisposed to that behavior, they may spawn local progeny that have the same aversive inclinations. If this is the case, anglers seeking them out may find that strategies such as more stealthy stalking and presentations made from longer distances are to their advantage, even if the fish are less pressured overall.

New available science and associated research is driving increased understanding of fish behavior, which will prove to be invaluable information for future generations of both fisheries managers and anglers alike.