Updated: Jan 14
Are you familiar with Pavlov’s dog experiment? Pavlov showed that dogs could be conditioned to salivate at the sound of a bell by associating a bell’s ring with food. After repeatedly feeding dogs after the sound of a dinner bell, dogs began drooling as soon as they heard the bell, even when no food was presented. This phenomenon is known as classical conditioning.
Other studies have proved that classical conditioning occurs not only in dogs, but also humans, and even trout. Through laboratory experiments, scientists have proven that trout are capable of learning, and remembering to associate certain actions with feeding. In a controlled study, trout that would strike at a red lever were awarded food pellets, and learned that striking the red lever would repeatedly present food. My point is that trout, who spend a large portion of their lives scanning for food items, are constantly learning from their environment, and applying that knowledge towards eating, and surviving.
Trout not only consider how much a drifting food item is worth calorically but also consider how much effort and handling time is needed to consume that drifting food item. Trout are constantly trying to maximize their caloric intake, and reduce the amount of effort needed to eat an item. This balancing act can be described as a ratio between E (energy of food)/H (handling time of acquiring food). This internal balancing act might explain why trout tend to fill up on salmonfly nymphs more so than the adults. Typically, trout feed on the helpless nymphs drifting in the current, as opposed to the adults that frantically struggle on the surface. Not to mention that the adults are capable of flying away before getting consumed. Trout can get so keyed into this balancing act, that they develop specific search images when they feed. A specific search image helps an individual trout correctly detect food passing by, and not misidentify non-food as food. And we all know that visual cues are very important to how trout develop these specific search images. However, trout don’t have a perfect knowledge of passing food items. They must experiment and learn to develop their searching image.
Seasonal changes present new food items, and new debris, leading to adapting and changing what a meal looks like. Further, trout settled in deep pools mid-channel might develop different searching images than trout hanging tight to the bank. The easiest prey item for a mid-channel trout in a deep pool might be a small nymph, while the trout holding in faster riffle might favor a drowning terrestrial. In a deep pool, the nymph wouldn’t require much energy to consume, as the fish don’t have to fight the current but still get an energetic reward, while the fish in the riffle might need to struggle to maintain a position, but may find a more energetically rewarding meal, such as a large terrestrial. Now, consider that temperature can influence trout cognition, and colder water not only limits metabolism, but also influences mental faculties, and foraging habits. Colder water could lead to greater handling time for certain items, a fish might not be as willing to swim up to the surface to eat a dry fly when a small midge drifting right in front of the trout’s nose is available. Turbidity can have a similar effect. As it becomes harder to see in a muddy river, fish choose to move into slower water to give themselves more time to consume easy prey, reducing their energy expenditure. Low light has a similar effect, with fish taking lies is slower velocity to gain a better field of vision for feeding. (Brown trout have been shown able to feed in light conditions as low as that provided by starlight.)
Competition with other trout and the hunger level of a fish also influence foraging behavior. Dominant trout maintain the best areas, and have larger habitat patches to forage, leaving subordinate trout to pick up the scraps in suboptimal habitat. Meanwhile, every river trout is fighting the current, expelling energy, eventually getting hungry. When hungry enough, subordinate trout make riskier decisions to forage out of cover, or in faster water, in hopes of satiation.
Now let’s consider the decision making of a “picky trout”. Maybe you’ve come across this trout. This trout is the bastard that refuses to eat your fly. He might look at it, swim over to it, even gently nudge the fly, but he doesn’t take it. He is likely a large, older fish, and has experienced many encounters with anglers, including a few where he was fooled. For all intents and purposes, he is picky. Painfully picky. I am starting to recall some of my picky fish encounters, and wondering if understanding the trout’s brain could have helped me. How could I have more quickly identified the fish’s searching image, and rang the proverbial dinner bell?
Back to Pavlov’s dogs, I’ve explained that conditioning is a learned behavior. The dogs learned to associate the bell with food when the bell is otherwise meaningless to dogs. Translated into fly fishing, we need our flies to match a trout’s specific search image, to convince the fish that the fly would maximize the E/H ratio of potential food sources. Fish learn to eat certain items, during a hatch, even over the course of a year. The key is to find the fly that mimics the food source. Pretty straight forward right? This is fly fishing 101. See a caddis in the air, fish a caddis dry fly...except when it isn’t straight forward. Picky trout aren’t playing along, something is holding them back. With all the experience they have watching drifting debris, sorting through objects to identify food, the fly you presented doesn’t cut it.
If we specifically consider a trout’s searching image, a trout’s refusal of my fly that tells me that my approach isn’t doing a good enough job imitating the natural food items the fish is searching out. Aside from the glaringly obvious fact that a fly isn’t food, (it is, in fact, a thin piece of metal with fur and feathers pinned to the shank) is the fly imitating the size, color, or profile of the food source? If not, how can an angler better match the food sources for picky trout? We must match our flies to a particular food source in a way that a trout doesn’t hesitate to eat the fly, as it is preconditioned to do so in accordance with the E/H ratio.
Alternatively, you might be better suited to present a food item that a trout doesn’t have a strong search item for, but looks to be of a high E/H ratio. This second consideration is best explained through another laboratory finding. In a controlled study examining trout feeding behavior, trout were regularly fed brine shrimp at a constant rate. Then researchers introduced a limited supply of crickets or mealworms, food of greater caloric content. When these calorically dense food items were presented semi-regularly the trout simply ignored the brine shrimp in favor of the other items. So much so that some brine shrimp even hit the trout in the face and yet were still avoided. But the key to this study, from an angler’s perspective, is the semi-regular introduction of crickets and mealworms. If too much time passes, the trout switched back to feeding on brine shrimp, likely due to an increased hunger state. In a nutshell, this offers an explanation for how trout change their feeding habits throughout a season. So when appropriate, a high E/H food item, similar to a cricket/mealworm, could overwrite the search image of a picky trout.
Understanding how trout learn can provide several advantages to the angler. First, trout can be habituated. Meaning they can learn to get accustomed to certain actions that don’t lead to negative consequences. Trout are likely habituated to most debris that floats past them in streams. Also, laboratory examples have even shown that trout stopped reacting to simulated predatory bird movement overhead. This is great news for anglers fishing on heavily pressured tailwaters. Fish likely know you're there, they just don't mind. It's even possible that catch-and-release practices have accustomed trout to being hooked.
But, getting one of these fish to eat is another thing. What if the picky trout you’re stalking was recently hooked? Do they recognize certain fly patterns as danger?... How long do fish remember? Some experiments have shown trout can remember bad tasting food items for up to a month. Other evidence suggests that trout can even remember certain food items for up to 3 months. However, water temperature may influence memory span, it’s likely that natural selection has favored cognitive abilities that coincide with different species optimal temperature ranges. (See our article about stream temperatures for reference). In regards to getting hooked, rainbows have shown “hook avoidance” after being caught, even starving for a number of days before feeding again. This may present a positive feedback loop for these fish, as starvation leads to a desperate hunger state, which in turn leads to riskier foraging, which could, in turn, lead to getting hooked again. Therefore, a picky trout might just be a trout in the wrong phase of this cycle.
Let’s assume that you find yourself in front of a picky fish that is feeding. First, the average angler needs to be observing their surroundings better. I have never, EVER, seen anyone other than me use a seine on the river to identify bugs drifting in the current. I’d rather find out for myself what’s in the river, at that very moment, then trust the word of someone else, even someone working in a fly shop ...you can’t be sure that second-hand information is current or up-to-date. You can buy paint strainers from Home Depot for cheap, and they work great as a seine. Just slide it over your net and hold it under the top 2 feet of the water column for a minute. You’ll be immediately clued to drifting insects. Next, try the bottom of the water column without kicking up any rocks. That could clue you in to what’s happening in the lower water column. Finally, you can kick up rocks in front of your seine to determine what other insects might be in the stream. Especially with the drifting insects, these insects are likely currently or soon-to-be hatches that fish will be cueing on. If you're lucky enough to catch a fish, you can use a stomach pump to get a quick look at what's on the menu and speed up your decision process!
Despite having this newfound information, the angler still has a potential problem. What happens when you don’t have any flies that mimic what you’ve found in the seine? Unfortunately, that can be an issue that’s hard to overcome on the water. On the other hand, it’s a fairly straightforward issue to address in the fly shop or at the vise. Basically, to predict the unpredictable, you need to be ready for anything. Come prepared with various sizes, colors, profiles. All good things to consider, and vary. Remember, you’re trying to match a very specific searching image. A trout wouldn’t be very picky if his searching image is generalized. You’re hoping to find a pattern that elicits a reaction similar to the dinner bell ringing for the dogs, where the trout identifies the fly as a match. If you are successful, you’ll find that a picky trout isn’t really a tight-lipped trout. He’s just looking for a very specific trait in his food. The trout has simply been naturally conditioned to associate his prey with a particular size, color, profile, etc..
Now, let’s consider a different kind of conditioning called operant conditioning, where the strength of a behavior is modified by reinforcement or punishment. So through operant conditioning, a “picky” trout, might choose to eat a safer offering (not getting hooked) compared to an offering associated with punishment (getting hooked). Individual fish will have unique preferences based on their life experiences, calling back to their size and position in a social hierarchy, hunger state, search image, memory, and environmental conditions. Still some general rules might hold true. For example, a picky trout might reinforce smaller items as safer (since anglers often fish the largest flies they can get away with), while eating something larger is punished (getting hooked by an angler), even if larger items are present.
Though not totally relevant to the topic of picky trout, there is another form of conditioning I want to acknowledge, known as observational conditioning or social learning. This describes learning behavior by watching and copying others performing that behavior. This type of conditioning could explain how stocked trout start to act like wild trout when introduced into the wild. It might also explain why certain rivers have certain fishing characteristics. The Gunnison River in Colorado is known to produce trout on orange dry flies year-round, like the Orange Asher, or Gunnison Stimulator. Could it be that young trout are brought up in the Gunnison River “culture” and learn from mature trout to eat these items? You might call b.s., but there are certain rivers where specific patterns or fishing styles dominate, and based on this entire discussion, trout memory and learning play a role--the fish has to ultimately decide for himself to eat your fly or not. I would argue that the continued success of these types of trends are the result of trout preference and not merely the food base. I don’t believe an orange food base exists year-round in the Gunnison Basin to keep trout’s attention that long without another explanation. I’ve seen orange flies referenced in fly books dating back to the late 90s, but it is still considered a good choice to this day.
Whew! We're almost to the end. Thanks for sticking it out. Obviously, there is a lot to digest here. This article specifically represents how I digested and interpreted information on trout behavior. But if this topic interests you, I highly recommend “The Mind of A Trout” by Thomas C. Grubb, Jr. There might be additional insights I overlooked that prove relevant to your fishing experience. Nonetheless, having mulled through all this trout psychology,
I'm fairly certain that a picky trout is capable of easily being caught. It’s simply a matter of understanding the factors influencing a trout’s decision-making process, and beating the fish at its own game.
As a guide for anglers, I’ve also compiled my playbook for dealing with picky trout, in hopes of distilling the above information into an approach other anglers can implement when preparing for, fishing to, and hooking picky trout.
Now that you're prepared with this background in how trout think you should read our follow up post, "The Picky Trout Playbook".