Why Fish Are Wary | Fly Fishing Insider Podcast

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Fly Fishing and Why Trout Are Wary

Predator Bear Eating Salmon - Wary Fly Fishing

Let’s take a look at feeding and fleeing scenarios and why scientifically fish are wary. We can prepare ourselves for the best ways to tackle these and other situations. Understanding the action being applied in accordance with reasonable behavior can set us up to be successful in situations. Most importantly we are taking the proactive approach to identifying wariness so we can avoid it altogether and keep fish in their feeding mindsets.  A feeding fish is the best target so let’s keep them in that stage by governing our activity and thus their sensory systems regarding Presentation, Environmental Disturbances, Sensory Alerts, and Preditors.
Understanding the sensory systems of trout first will enable us to relate to the various responses we see from them when they are wary. The lateral lines, eyes, ears, and nose of a trout are way too often overlooked in many aspects.  We often pay attention to forward and up connicle sight and the sensitivity of sound for trout but do we have a grip on how it physically works?  I would venture to say that most are very weak in the understanding but realize there is an importance so they take drastic yet minor and futile measures. Let’s get scientific and work on moving away from futility and towards effectiveness in our governance of the sensory system’s ability to detect and trigger wariness. 

Lateral Line
Trout rely on their lateral line system, an intricate sensory mechanism, for a variety of crucial functions that are fundamental to their survival and interaction with their aqueous environment. This system, consisting of a series of fluid-filled canals and sensory units called neuromasts located along the sides of the fish, detects vibrations and changes in water pressure. As fish swim, or as other objects move nearby, the displacement of water creates pressure waves that the lateral line picks up. This allows fish to navigate through murky waters, avoid obstacles, detect prey, and communicate with one another through subtle water movements. It also plays a vital role in schooling behavior, enabling fish to synchronize their movements with precision and grace. By processing the information gathered through the lateral line, fish can respond to their environment in real-time, a testament to the evolutionary refinement of sensory perception in aquatic life.

Tip: Vibrations are measured in hertz and and have been a nemesis to anglers who have attempted tp define the right measurement to trigger eating habits. 


The eyes of a trout are marvels of evolutionary adaptation, conferring acute visual acuity which is critical for the fish's survival and interaction within its aquatic realm. Positioned on either side of the head, trout eyes are optimized for a wide field of view, allowing for an almost panoramic awareness of their surroundings, which is essential for spotting predators and prey. The trout's retinal structure is rich in rods and cones, granting them excellent low-light vision and the ability to discern colors and contrasts—abilities that are crucial in the dappled light of their freshwater habitats. Furthermore, their eyes can detect polarized light, helping them to see past the water's glare and surface reflection, an advantage when hunting or evading threats. This visual system supports the trout's predatory lifestyle, as they feed on insects and smaller fish, requiring the precise timing and accuracy that only sharp vision can provide. The eyes of a trout are not just mere organs of sight but integral tools that have been finely tuned to ensure their success within the dynamic tapestry of riverine and lacustrine ecosystems.


The ears of a trout, often simplistically overlooked when considering the sensory adaptations of fish, play a significant role in their environmental perception and survival. Unlike terrestrial creatures, trout have internal ears, with no external openings, situated below the surface of their skin. These ears consist of otoliths—tiny, calcified structures that float in a gel-like substance within the ear's semicircular canals—and hair cells that detect movement and vibration. This setup allows the trout to perceive sound through the detection of particle motion rather than pressure waves, which is particularly useful underwater where sound travels faster and over longer distances compared to air.

The auditory capabilities of trout are integral for detecting the presence of flowing water, predators, or the movement of potential prey. They also contribute to the fish's sense of balance and spatial orientation, helping them to maintain their position in varying currents and when executing intricate swimming maneuvers. Moreover, the sensitivity to sound assists in navigation during migration to breeding grounds, as they may rely on auditory cues to locate specific river sections they have imprinted on as juveniles. The trout's ears, therefore, are not mere instruments for detecting sound; they are sophisticated systems that facilitate a complex interaction with the aquatic environment, influencing everything from foraging behavior to social interactions and migratory patterns.

Fly Fishing to Wary Trout


The nose of a trout is an exquisite example of chemical sensing sophistication, serving as a vital organ in the fish's repertoire of survival tools. In lieu of a prominent external nose, trout possess highly sensitive olfactory sacs, which open to the exterior through tiny nostrils called nares. Within these sacs, an array of olfactory receptors binds with dissolved substances, allowing trout to detect a myriad of chemical signals within the water—signals that convey profound information about their surroundings.

This olfactory system is crucial for several aspects of a trout's life. It guides them in locating food, and discerning between edible and inedible items with astonishing precision. It is also indispensable for reproductive success; trout use olfactory cues to identify suitable mates and spawning sites, often influenced by the unique chemical signatures of the waters where they were hatched. Furthermore, the trout's sense of smell plays a crucial role in their remarkable homing ability, enabling them to return to their natal streams to spawn, sometimes after years at sea and over thousands of kilometers of migration.

The trout's nose, therefore, acts as a chemical compass and a detailed sensor of the aquatic landscape, decoding the complex chemical tapestry of the water column to navigate, feed, avoid predators, and perpetuate their species. It's a testament to the intricate evolutionary design that enables trout to thrive in diverse and often challenging freshwater environments.


The sense of touch in a trout’s face and mouth is exquisitely fine-tuned, serving as an essential facet of its feeding strategy. The mouth, surrounded by supple and sensitive lips, lined with minute taste buds, and the snout, which often bears tactile receptors, together create a tactile feedback system of exceptional delicacy. As a trout forages, these touch-sensitive areas are used to probe, nudge, and ultimately discern the texture and suitability of potential food items.

When a trout inspects or seizes an object, the nerve endings in the lips and mouth register the contours, firmness, and movement of the prey, allowing the fish to make split-second decisions about whether to reject or swallow it. This sense of touch is particularly crucial in habitats where visibility is poor or when the trout feeds at night. In such scenarios, the tactile sensation becomes a primary source of information, guiding the trout to edible prey and away from inedible detritus or harmful objects.

Moreover, the trout's mouth, particularly in species like the brown trout (Salmo trutta), often has fleshy, finger-like projections called "barbels," which provide additional tactile feedback. These barbels can detect movement and vibrations, giving the trout another means to locate and evaluate potential food sources in their benthic foraging zones.

The trout’s tactile abilities are thus an indispensable complement to its other senses, ensuring efficient and discerning feeding behaviors. This sensory integration showcases the trout’s remarkable adaptation to its environment, enabling it to exploit a wide range of food resources with precision and agility.

Okay, now diving into the details of how the sensory systems come into play regarding the three categories of Presentation, Environmental Disturbances, System Alerts, and Preditors will help simplify the approaches we take. Boiling this ocean of information is critical to success and can easily improve the skillset of most anglers as it tends to be over simplified.


Feed: When a fly mimics the natural food source in silhouette size, color, and movement (presentation), fish are more likely to bite. For instance, during a mayfly hatch, using a fly that closely imitates the silhouette, size, and color of the emerging mayflies can entice fish because they recognize it as familiar food.

See the OSSCP method of fly selection article.    

Scientific Reason: Fish have evolved to recognize specific prey items in their environment. Over time, they've developed an innate response to target prey that fits within their expectations of appearance, size, and movement. Knowing how fish see with their field of vision and how accurately presented flies can keep a sensory system from alerting changing perspective for an angler.  Now the understanding of the presentation goes further than a particular look. Instead, from top to bottom, was the entry okay, was it entered at the correct point, was the drift accurate, and is the food source in the correct realm of the food source or sources expected   

Understand Zone based presentation in this article.     

Flee: When the fly lands too hard on the water or drifts unnaturally (drag or micro drag), it can raise an alarm via the sight and or feel of unnatural movement. Perfecting your drift can directly affect this sensory alert.  Additionally, you must ensure that the drift is natural in the correct zone. At the same time, using a fly that doesn't match the silhouette or size of the local hatch can spook fish.     

Scientific Reason: In their natural environment, sudden disturbances on the water's surface often signify danger, like a diving bird or slapping a small fly. Lateral line and ear detection of disturbances or vibrations in the water triggers a fleeing response. An unnatural drift or appearance of an object can signal it's not genuine prey and do the same. These are evolutionary systems triggering responses in fractions of a second and not always with accuracy but often overly protective so it’s best to attempt to avoid the triggers at all costs.

Environmental Disturbances

Feed: Overcast days can lead to more active feeding as the diffused light makes fish feel safer from aerial predators. The polarized vision of trout is affected by low light similar to yours with the polorized sunglasses. Rain can wash terrestrial insects into the water, triggering a feeding frenzy but rarely shuts down all caution regarding sensory systems.

Scientific Reason: Over millions of years, fish have evolved behaviors to maximize feeding while minimizing exposure to threats. Low light conditions provide a perceived reduction in threats.      

Flee: Casting shadows, making loud noises, or wading clumsily can spook fish, making them less likely to bite and more likely to hide. Listen to this podcast tip advising you to “fish like a cat” by using similar stealth-like stalking techniques.  

Scientific Reason: Shadows and sudden noises can be associated with predators. Fish have a lateral line system that detects vibrations in the water, so clumsy wading can be felt and interpreted as a threat. The same goes for being up stream or slightly down stream of a fish and causing the hydraulics of the water to be altered and setting off a response. 

Sensory Alerts

Feed: Vibrations or disturbances that mimic struggling prey can attract fish. For instance, a twitching fly can imitate a wounded insect or small fish.

Scientific Reason: Predatory fish are attuned to the vibrations of struggling prey, and their lateral line system can pick up on these cues.   

Flee: Foreign scents on flies or the line, like those from sunscreens or repellents, can deter fish. 

Scientific Reason: Fish have an acute sense of smell. Any foreign or unnatural scent can be a signal that something is amiss.

Eagles making trout wary. A fly fishing nightmare.


Feed: Fish often feed more aggressively after the perceived threat of a predator has passed, trying to quickly get nutrients while the coast is clear.   

Scientific Reason: This is a risk-reward calculation. After a threat has passed, there's a brief window where the reward of feeding outweighs the risk of exposure. Fish are opportunistic and the opportunity can often outweigh the risk. Whether it is short memory or not, food is always on the mind of fish.    

Flee: The mere sight or sensation of a predator, whether it's a bird's shadow overhead or the vibrations of a larger fish, can send any fish into hiding. The level of wariness can vary from moments to what feels like months!

Scientific Reason: The instinct to avoid predators is deeply ingrained. Any sign or sensation of a predator triggers an immediate flight response.

Remembering these categories and the underlying reasons can help your fly fisher in multiple ways.  You are better off understanding fish behavior and improving your chances of a successful outing. My best advice is to fish like a cat. The level of stealth you execute will directly affect your chances to target trout.  Next execute with precision, accuracy, and a little luck.

 Christian Bacasa, Host of the Fly Fishing Insider Podcast

By Christian Bacasa
Host of the Fly Fishing Insider Podcast

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