Fish Behavior

Bass have lateral lines to detect movement.

Professional anglers work hard to figure out where the fish are. That’s job one. Then, they try to figure out what those critters might want to eat at that given moment. Then, they catch a limit, hopefully with at least one “kicker” (big fish) and head to the weigh-in station to win the big money.

Sounds pretty simple, doesn’t it?

It’s not.

Those pros, almost to the person, have intuitive knowledge of fish behavior to the extent they can almost “feel” it. Then, they have to figure out where the fish might be at any given moment so they can use that intuitive thinking to urge a strike from enough quality fish to give themselves a chance of winning.

Bluegills make beds and guard them during spawn.

Fish behavior is such a simple concept wrapped in such complicated trappings.

Here’s the simple part.

Fish don’t have the brain parts to “think”. They can’t reason, they can’t select or choose due to any type of cognitive thinking. They react…based on instinct and conditioning. Instincts are centered on several fundamental concepts…breeding, feeding, defense and offense. That’s pretty much it, depending on the species. Their behavior is centered on those instincts and whatever life circumstances are imprinted in their little bitty brains.

Catfish conditioned to eat fish food.

Much of their behavior is based on conditioning, a Pavlov’s dog’s concept, especially as a fish gains a few years. If a fish swims through an area and finds food, it’s likely to come there again. If a fish is attacked at a certain spot in a pond and it happens again, it’s likely not to come there again.

Here’s where it gets complicated.

Fish’s senses work together to allow its instincts and conditioning to dominate its behavior at any given moment.

Here’s what that means. Each species of fish has several senses, some in varying degrees depending on species. Vision, smell, touch, hearing, and their lateral lines combine to send stimuli to the brain, instinctively influencing that fish’s behavior at that moment.

These bass were ‘trained’ to eat fish food, not their natural instincts.

A hungry bass’ stomach sends notice to its brain to eat. That puts the fish on alert, heightening its sensory systems. Eyesight kicks in and the fish starts looking for potential meals. Its poor ability to smell doesn’t help much, but its good eyesight and its lateral line work together to zero in on something tasty and nutritious. The lateral line, that long tube you can see along the middle of its body on both sides just below the surface of the skin, detects pressure changesin the water and sends an impulse to the brain. Based on repetitive conditioning, an older bass can instinctively pursue its quarry depending on the type of pressure change it feels through its lateral line. For example, say a school of shad is moving in unison thirty feet away. The bass’ lateral line picks up that movement. Its brain then must quickly interpret. Its lateral line’s job is to interpret movement through impulses and, over time, condition a reaction. A bass’ nature is to investigate any movement in water. When the bass investigates, its eyes then become the dominant sensory mechanism. Even though that bass couldn’t see the school of shad at first, it moves in that direction, then when close enough to see, instinctively attacks and feeds, inhaling as many shad as it can.

What about those shad? They move in a school as a defense mechanism. Moving in unison, a school of shad can be sensed by potential predators at a distance as one big fish. Hopefully, for the school of shad, those predator fish below will sense the movement, instinctively interpret that movement as one big fish and leave it alone. Here’s where it gets quite interesting, though. When that big bass above does move in to investigate and sees all those little fish and then makes its burst to feed, the shad respond instinctively. Next time you see a shad, look at it closely. Gizzard shad and threadfins (and most other species of shad) have a black dot toward the back of the fish. Scientists think that black dot is also a defense mechanism. Here’s why. When a predator fish feeds, it strikes at the eye of the fish. Chasing a shad, that bass has a 50-50 chance of striking at the black dot. That dot resembles an eye. If the predator strikes toward the back of the fish, the shad stands a better chance of escaping. That’s not all…when a bass makes its burst into a school of shad, the school reacts by going in a thousand directions, fleeing its fate. A bass, using its vision, is confused by all the movement. It can’t decide which shad to chase. So, instinctively, bass chase what they see and that school of shad flees the chase. Both species use their instincts to survive.The bass may get a meal and the school of shad escapes largely intact…missing a few members.

Redear sunfish behave differently than other sunfish.

Channel catfish behave quite differently. They tend to be cautious, except larger fish when they are actively feeding. A channel catfish’s nature is to be wary. When something hits the water, channel catfish flee, where a bass instinctively investigates. But, that channel catfish will come back in a few minutes, especially when the item that hit the water sits still…on the bottom. An old river fisherman taught me years ago. He said, “When you cast your bait, let it fall to the bottom and leave it there. After a few minutes, a catfish will come and check it out.” He was right. Not only will they check it out, his next line of advice was on the money. “Don’t set the hook on a catfish immediately. Wait until it runs with the bait.” Here’s why that’s good advice. Channel catfish have taste buds on their whiskers. They “bump” their food to taste it before they eat it. If it tastes good, then they eat it. What about those larger channel catfish? The bigger they grow, the more predatory they become. Channel catfish are commonly caught on artificial lures when they are actively feeding. But, their nature is to be wary and taste their food before they eat it.

What about sunfish, like bluegills? Based on that fish’s lifestyle, its senses help dominate its behavior. Most sunfish are schooling fish. But, they are also carnivorous predator fish, limited by mouth size. Their movement tends to be reflexive, based on stimuli. If an insect hits the surface of the water, bluegills immediately go at it. With eyesight, they converge to eat the critter, even though they don’t know exactly what they are eating. All they sense is that hundreds of their buddies have the same idea and the first one to the prize gets it. If it tastes bad or doesn’t feel good in their mouths, they spit it out. Then, the next aggressive one tries its hand…or mouth.

One male bluegill defending its nest against an intruder.

Understanding fish behavior takes time, study and observation. Most fascinating is to study and watch different sizes of different species of fish, how they behave and how they interact in a community. The dynamics of those interactions provide lots of fun and entertainment and is worthy of your time…especially at pondside with your favorite beverage. Watch how your fish behave when you pitch a few nuggets of fish food to them. Watch how they behave during their spawning rituals next spring. Watch how the shad blow up this fall as bass lunge into the school. Seeing is believing…believing leads to understanding. Understanding leads to being a better steward of your favorite wet spot.

And that, dear pondmeisters, can lead to a better instinctive understanding of our conditioned lives.

Bob Lusk is a 36-year veteran private fisheries biologist and lake consultant, traveling the nation helping people design, build, stock and manage private fishing waters. He is the editor of Pond Boss magazine, the nation’s leading journal on pond management. He can be reached at [email protected].