The Basic’s of Freshwater Fish

Basics of freshwater fish

To be a successful angler understanding how fish use their senses to feed, spawning habits are key to catching fish consistently.


Fish live and adapt in a fluid, highly pressurized underwater environment. Predators and prey co exist in close proximity competing for food and shelter. Survival is based on a refined set of primary senses, vision, hearing, taste, smell and the lateral line enable them to find food and detect danger.

Lateral Line:

Sound travels five times faster underwater than in the air. Fish are equipped with a number of sound and vibration senses. The lateral line is a series of nerve endings along the fish’s sides, it senses underwater vibrations helping the fish determine direction, speed and size of prey or predator. In off-colored dark water the lateral line is key to its’ survival, as well as enabling the fish to feed, escape predators and act as a radar detecting fixed objects along with swimming together in schools.


Fish lack external ears and hear sound through an inner ear that is similar to mammals and other vertebrates. It is composed of three semicircular canals that help fish maintain their equilibrium and balance. In other words, the inner ear allows fish to swim right side up in water with no light or other limited visual cues.

Similar to animals and humans, fish eyes have receptors called rods and cones in the retina which provides vision. The rods detect light intensity, the cones identify colors.

The eye placement on fish allows for a wide field of vision in most directions with the exception of straight back or down. The optimum presentation of a lure or bait is in the front or above the fish. This explains why surface or fishing in the top water column is so successful.

Most predator fish posses strong eyesight and can discern colors. Bass, pike, salmon, trout, walleyes and muskies have shown that a certain lure color pattern draws more strikes than others. Studies have established that largemouth bass will strike at red lures more than any other color. Lake trout favor silver, pearl, chartreuse, or combinations of these colors. Steelhead trout prefer pink, red or orange with combinations of silver and pearl, brown trout use brass or copper finished lures. Walleyes green, chartreuse and orange. Muskie & pike; black, orange, chartreuse, white, green with combinations of silver, gold and copper.

Water type and time of day acts as a color filter. The vibrancy of colors lessens in deeper and stained water. As the sun goes down red is the first to disappear then yellow with greens and blues last. At dawn when the sun enters their world blue, green are the first colors fish will see, red being last. Water clarity affects the distance fish can see, in very clear water fish can see well over a 100 feet unlike dark or cloudy water that limits vision to only a few feet or inches.

Percentages of Color Visibility Underwater
(Percentages of Visibilty %)

Color10 Feet20 Feet30 Feet


Fish smell as water is drawn through a front opening on the snout and passed through the nasal sac and expelled. The Salmon have a highly developed sense of smell by which they can detect one part per billion of odorous material in the water, enabling them to swim hundreds of miles tracking the odor of water to which they will return the exact spot where their lives began. Odors also alert fish to the presence of danger. When a predator attacks baitfish, a chemical is emitted that warns other baitfish to flee. Bottom feeders such as carp, buffalo and sturgeon rely almost entirely on upon their sense of smell to feed.

As many fish have a highly developed sense of smell, most predators use other senses to find food. Vision and the lateral line will enable predators to find prey quickly and more effectively.

The taste sense is of minimal importance to most game fish with the exception of catfish and bullheads that have taste sensitive whiskers which allows them to test food before eating it. Knowing this, the stronger or smellier the bait, the better for catfish.

Feeding & Food:
Young fish learn what is and what is not ediable by approaching food with caution and test it before swallowing. As the fish matures they build a list of preferred forage, some seasonal with insect hatches and other times they must eat what is available.

Fish use different techniques when feeding, Panfish, bass, walleyes and trout inhale their prey by sucking in water and the food. Other toothy gamefish such as northern pike and muskies strike their prey crosswise with their long sharp teeth holding it until it stops struggling then turns it headfirst to swallow. Salmon swim through schools of baitfish, slashing their tail stunning baitfish to feed upon.

The preferred choice of prey for gamefish are soft rayed minnows, ciscos, and suckers which can be swallowed easily. Insect hatches, such as the mayfly, are also a favorite meal for trout, perch and walleyes. Other forage includes: Crawfish (Smallmouth Bass) Frogs and Salamanders (Large Mouth Bass) Leeches (Walleyes & Panfish) Alewives & Smelt (Salmon).

With all water-based ecosystems the food chain is the key to sustaining life. The food chain starts with algae or phytoplankton growth that feeds a microscopic animal named zooplankton. Minnows and young game fish are called “fry”. These young fry feed on the zooplankton which then feeds the small and large predator fish. Sunlight is crucial for photosynthesis, which is the energy that starts the process, allowing plants to grow and supply oxygen to water. Water ecosystems also have filters cleaning the water such as clams and mussels. This cycle repeats when the dead matter from winter provides the nutrients required to start the algae growth in Spring.

Most freshwater game fish spawn in early to mid spring with the exception of catfish and native trout, which spawn during the summer, and salmon that spawn in the fall. This annual ritual brings game fish from the depths to shallow warm water. After spawning is completed they return to deeper water to recuperate. There are two main categories of spawning habits game fish use: Random, which is distributing eggs over an area of vegetation or rock and gravel. Nest Builders (Redds) A nest constructed by the female fish where eggs are deposited and fertilization occurs. Nests can be distinguished in the water by a cleared depression. The main determining factor on when spawning occurs is the water temperature.

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