Fish Factors: Items That Influence Your Fishing Success

 The following article by the Loveland Fishing Club's Walter Graul appears in the Colorado Outdoors Fishing Guide 2026. The guide is available for purchase from the Colorado Division of Wildlife. Shop - Colorado Parks and Wildlife IPAWS 

By Walter Graul

In 1653, Isaak Walton published The Compleat Angler. Since then, literally millions of publications have been produced globally about fishing. Many are focused on how to increase fishing success via how to fish and where to fish. A modern trend is to focus on new technology, impacting everything from improved reels and graphite rods to equipment like electronic fish finders. The latter has evolved to LiveScopes that can cost from $2,000 to $3,500. These are frequently called "Fish TV." The 2025 Bass Pro Fishing Master Catalog has 500-plus pages of fishing equipment and clothing.

 But have you ever had a great day on the water and gone back to the same spot the next day

with zero luck? Or perhaps you have experienced a day where fish are feeding in a frenzy and

suddenly they quit biting? This may be explained by a basic understanding of how various

factors influence fish behavior. This certainly can result in increased fishing success. It can be

applied with the most basic equipment like most of us started fishing with—rod, reel and

something at the end of the line to attract the fish. Thus, the remainder of this article will address

these key factors and relate them to fishing success. Some of the information will be well known

to accomplished anglers, but hopefully there will be some new information for all readers.

Thermoclines

 A thermocline is a distinct layer found in lakes where water temperature changes rapidly with

depth. There is a warmer upper layer of water with a deeper, cooler layer. It is a barrier to mixing

and traps low oxygen levels below the line. Fish tend to stay above or in the thermocline for

optimal oxygen levels and temperature. The thermocline can look like a blurred line on

fish-finder sonar. These tend to form at deeper levels in deeper water. Fifteen to 20 feet is a

common depth, but this can vary widely. Fishing at the thermocline level can add to fishing

success in the warmer months. They are subject to seasonal changes and form in late spring to early summer as the water

heats up.

When temperature begins to drop, the upper layer cools, becomes denser and sinks.

This mixes the two layers and creates fall turnover. This frequently happens in Colorado from

late September to mid-October. One of the most complete discussions of this is by Brad

Peterson in his online edition of NoCo FishingNews. He notes the turnover can create a murky

color. Often fishing is difficult until things clear up. This is because of a change in oxygen levels

in the water column with temperature variations. This can change baitfish behavior, and fish also

have lowered visibility. Fish can become very inactive during this period. Peterson suggests

trying different lakes and targeting moving water among other things.

Barometric pressure

Barometic pressure is the weight of the air pressing down on everything on earth including fish. This pressure can be affected by altitude, weather systems and even heating from the sun. Fish detect changes through their swim bladders and lateral lines. Slight pressure changes can cause major variations in fish behavior.

A falling or rising barometer can stimulate fish feeding. They can be particularly active just

before and during a rapid low-pressure drop. This is a good time to use more aggressive lures

and presentation patterns. However, a pressure drop tied to something like a major cold front

can really shut fish down. As the pressure rises after such a front, fish may still be less active

and move deeper. However, an extended high-pressure period can cause stability, with fish

more active. So, pressure has a highly variable impact on fishing. The best advice is to fish

often, with rapid low-pressure drops being high-priority times.

A couple weather changes associated with pressure can have major impacts upon fish feeding.

A sudden rainstorm can decrease light and thereby provide more security from predators. It also

can bring in more food, and the cooling of the water boosts oxygen and can stimulate feeding. I

have experienced times when fish fed in a frenzy during the rain and then stopped immediately

when the rain stopped—especially if the sun then came out.

Likewise, wind is an important variable that relates to pressure. It is not unusual to have slow

fishing with a calm wind that suddenly improves even with a light breeze. One speculation is

that even these light breezes can provide some security from predators and stir up food like

phytoplankton and invertebrates. Some say it somewhat blurs the lure presentation such that

fish must decide whether to react without clear detail of the lure, fly or bait. Stronger winds also

can push bait fish against a shoreline. The best fishing is casting into the wind along that shore.

Strong winds in lakes can really impact baitfish and cause some fish to feed aggressively.

Warm-water anglers know this as a "walleye chop." The take-home message of all this

is that when weather sends many anglers heading for cover, it can be worth grabbing the rain gear

or other warmer clothing and fishing aggressively.

Solunar theory

This theory is founded upon the fact that combined gravitational forces of the sun and moon

create tides. Some claim these same forces impact all animals, including inland fisheries

species. There are solunar tables targeting hunting and others that target fishing. Major activity

periods occur when the moon is directly overhead or directly below a referenced latitude. Minor

periods occur when it is positioned 90 degrees to either side.

Based upon this information in the 1920s, John Alden Knight created the first solunar tables.

Since then, many such tables have been published, and they are readily available today. Some

anglers rely heavily upon the tables to decide when to fish (major periods are best), while other

equally knowledgeable anglers reject them, claiming there is a lack of scientific verification.

Perhaps the conclusion is the solunar effect may be one of the lessor impacts on fish feeding

behavior when compared to the other factors, but is still worth considering. If you want to try

using the tables, go to In-Fisherman.com and click on Learn. It provides data for your specific

location.

Light

To understand the impact of light on fish behavior, it's worthwhile to understand fish eye

structure. Like us, fish have rods for detecting contrast and movement. They also have cones

for color detection, while some even see ultraviolet and polarized light. They have round lenses

that focus on light by moving closer or further from the retina. With eyes on the side of the head,

they have a nearly 360-degree-wide field of view. Their only blind spots are at the nose and

directly behind them. Lacking eyelids make them sensitive to bright lights, especially for the

many fish adapted to low-light conditions. For the latter group, as the sun rises and gets

brighter, they tend to seek deeper water or shade. They will come back up as low light develops

in the evening. Some feed mainly at night, and some may be especially active during a full

moon.

Their highly sensitive eyes are particularly responsive to colors. This can have a major impact

upon fly or lure color choices. As light penetrates relatively clear water, red disappears first,

often by 15-30 feet. Orange fades next at about 25-40 feet. Yellow disappears at about 35-60

feet. Greens fade around 70-90 feet. Blue and violet can penetrate to the deepest levels.

How does this relate to fly and lure color choice in different situations? With bright light in lakes,

natural reflective colors like silver and white are good choices. In trout streams, silver, gold and

olive can be good. In more stained or murky streams, bright colors like pink, orange and white

can work well.

In lower light conditions such as dawn or dusk, or cloudy conditions or murky water, darker

silhouettes can be best. These include black, dark blue, purple/violet or even fluorescent.

Chartreuse is good, but I have found this color to be good in most light conditions. At night,

white, green or blue colors are good choices. In deeper waters, blue, purple and ultraviolet

penetrate the furthest. Of course, these are just general patterns. For example, the Ned Rig is a

popular soft jig and comes in at least 29 colors. An online search produces a plethora of color

charts available with detailed information and color recommendations for specific situations.

Temperature

Temperature impacts fish activity in many ways. It influences metabolism, muscle temperature,

growth rates, feeding patterns, spawning times and even basic survival. High temperature can

lead to unwanted algae blooms. In general, in the warmer months, trout seem to prefer water

temperatures of 50-65 degrees. When the temperature nears 70 degrees, it can put trout under

severe stress or kill them. Handling them can add to this stress. This is the basis for fish

biologists recommending stopping fishing for trout when the temperature nears 70. Some states

ask for a voluntary fishing closure on some waters around 2 p.m. in warm weather.

When temperature drops below desired levels, fish can become sluggish and less active. Since

major temperature drops can lower metabolism and muscle activity, this may explain why fishing

can slow down during winter or even through the ice. This also can explain why in early spring,

shallow water can be most productive since it warms the fastest. The north side of a lake may

be the best because it tends to warm the quickest.

Fish spawning is affected by temperature, and it varies for different species. Bass like water

temperatures in the 60-65 range in late spring or early summer. Bluegill like 70-80 degrees for

spawning. Walleye and pike will start spawning at 40-50 degrees. Trout like rainbows and

cutthroats are spring/summer spawners and will start the spawning process at about 40-50

degrees, which might not occur until July for trout in high lakes. For fall spawners like brown

trout and brook trout, the mid-40s are spawning time. In the Rockies, this typically occurs in late

September to early November, with October being a peak time.

The spawning periods can be very special fishing times. Commonly some of the bigger fish are

caught then. This is related to the bigger fish moving into spawning areas and being particularly

aggressive. This is a good time to use more aggressive lures, flies or bait presentations. Larger

can be better. This is the time flyfishers frequently switch to the bigger Woolly Buggers. Jerk

baits also are very effective with spinning equipment. This applies to both warm-water and cold-water species.

Fishing during spawning creates some special concerns. Some argue that it is unethical to fish

then because trout-egg nests (redds) can be stepped on. Also, fish mortality can be higher since

they are already under stress caused by long travel to get to spawning areas and defending the

nests. Because of the popularity and highly productive fishing during spawning times, it is very

unlikely that fishing then will be prohibited on a broad basis. You can help the resource by trying

to avoid stepping on redds. Release fish quickly and gently, and ideally by not removing them

from the water. If you do lift one out, wet your hands first and do not use gloves. Try to land the

fish quickly to reduce fatigue in the fish.

Digestion/metabolism

The interaction between temperature and metabolism greatly impacts fish feeding patterns

through affecting their digestion times. Digestion time also is impacted by the size of the fish

doing the eating and the size of the meal. Much remains unknown about fish digestion, but a

major Russian study by V. B. Tseitin is notable. He developed a formula that related digestion to

temperature. At optimal temps, digestion can occur in as little as 12-14 hours. However, for

warm-water species at optimal water temps of 68 degrees, digestion can range up to over 60

hours, but speeds up with warmer temperatures. Cold-water fish do the reverse. Their ideal

temperature is about 50 degrees, but as the temps warm, their digestion slows down. As

temperatures move from optimal levels, digestion times can go from hours to days, and days

into weeks.

This can explain at least two things, starting with fish not feeding at the same time on different

days. It can also possibly explain why in clear water you can make a perfect presentation that

goes right past a fish that ignores it. Even changing lures or flies does no good. It is just not

hungry yet!

Habitat structure

Habitat structure has a major impact upon your fishing success. However, there is one common

theme. Look for any type of habitat-structure change. Examples include shallow points that drop

into deep water, edges of weed lines, edges of mud lines, flooded trees and gravel, flow

changes in streams, and changes in the bottom substrate. Looking into habitat structure in more

depth will serve you well.

Final thoughts

Fishing success depends upon many interacting factors. Learning how this all works is a lifelong

process. The more you learn, the better angler you will become. There is an 80-20 rule in fishing

that says 80% of the fish are caught by 20% of the anglers, using 20% of the fishing spots or

with 20% of the gear. Another often quoted statement is that 90% of FEEDING fish are found in 10% of the available water. Acquiring knowledge and experience certainly concerns who catches fish

and who does not.

There are a few corollary thoughts related to the preceding paragraph. I grew up watching one

of the first hunting and fishing shows on television. It featured Harold Ensley from Springfield,

Missouri. His number one rule was to keep your line in the water, and if you feel something, jerk!

That also means the more time you spend fishing, the more fish you will catch. Perhaps there is

also some truth that every day spent fishing adds a day to your life. This theory may not be

proven yet, but sure worth being part of the study.

Walter Graul retired from a biologist career with The Colorado Division of Wildlife (now Colorado

Parks and Wildlife). He started in an entry-level position and retired as assistant director,

overseeing all biological programs. He also is a director emeritus of The Colorado Wildlife

Federation.