Bass Spawning Process Starts With Increased Sunlight

There are a few certainties in this world, and Ben Franklin nailed a couple of them: death and taxes. You could add high cell phone bills today, too. But there is another known quantity, a constant that though it changes by time of year, it’s very predictable. As planet Earth wobbles through space spinning at a thousand miles an hour, tilting back and forth toward and away from the sun, the seasons change ever so slightly and imperceptibly on a daily basis. Without notice, summer edges into autumn, and winter swallows you up.

Craig Springer fishing in the bow of the boat.

But change they do. As sure as the sun rises, astronomers know the amount of daylight that will occur on any given day in any given year in any given place on the planet. If you’ve hunted waterfowl or deer, you’re keenly aware of the very specific times of day when you can hunt — down to the minute, which change nearly every day of those seasons.

Days Getting Longer
If you’ve got the winter blahs right now, don’t let it get you down, because you may have noticed the days have gotten longer since the winter solstice on December 21. And trust this: bass have noticed, too! Granted, water temperatures probably haven’t changed a great deal since last autumn, depending on where you fish, and fishing is probably slow going in the still, cold depths of winter. But when those photons fire in the big helium sphere we orbit, striking Earth eight minutes later, something profound happens – – chemical reactions start to stir the primordial instinct in bass to procreate.

The black basses may not get on the nest until maybe April or May, but the chemical building blocks are being stacked and cemented together with hormones right now while ice may cover your favorite pond or cove, and getting down a boat ramp may be unthinkable.

Though bass don’t think or reason that the spawn is coming on soon, it is, and it’s going on in their heads, or at least it starts there, said Mississippi State University fish physiologist, Dr. Louis D’Abramo. D’Abramo is a professor in the Department of Wildlife and Fisheries, and is the associate director of the Mississippi-Alabama Sea Grant Consortium.

It All Starts With Sunlight
Increasing amounts of sunlight penetrates the water and ice. It hits their eyes and is the cue for initiation of the reproductive cycle, said D’Abramo.

“Fish sense the increasing daylight through their eyes to the brain, specifically the hypothalamus region and the pituitary gland, where important hormones are produced,” said D’Abramo.

Sunlight produced millions of miles away essentially stimulates in a bass’s brain production of a hormone called gonadotropin. These first hormones in turn cause the production of other sex steroid hormones in a bass’s ovaries and testes. These hormones in turn cause the eggs to develop in a bass’s ovaries, and eventually cause spawning activity. Male bass similarly turn on to build a nest and spawn.

Temperature and hormonal development essentially control one another to prevent premature spawn. While light may induce chemical changes in the blood stream, a change of appetite is eventual, but the metabolic rate is tempered by water temperature.

“There are both positive and negative feedback controls for this whole process that is often termed the hypothalamic — pituitary — gonadal axis in fish,” said D’Abramo. “Basically, it is an environmental change, seasonal in nature, that stimulates the brain to produce certain hormones that in turn stimulate the production of other hormones by the reproductive organs involved in achieving reproductive maturity and eventual spawning.”

Cueing The Spawn
But he cautions against thinking it’s the increasing amount of sunlight alone that cues the spawn.

“It is generally a combination of photoperiod [length of daylight] and temperature,” said D’Abramo. “This is a fail-safe system, just in case water temperatures rise unexpectedly before the best spawning conditions develop. Hence, the need for a greater length of daylight to increase the certainty to initiate the physiological process of the reproductive cycle.”

In North America, it takes a combination of increasing daylight and steadily warming temperatures to ensure the spawn. Were it day length alone, bass could be forced to spawn in water temperatures that would surely fail the spawn. It’s orderly, but not entirely predictable, with water temperature being the wildcard variable. Water temperature playing a part in the spawning cue also serves to conserve energy; the chemical building blocks are getting stacked with increasing daylight while the metabolic rate of the fish soon to spawn is tempered by determining water temperatures.

In areas more tropical, especially near the equator, the day’s length is not a stimulus for tropical fish because there is essentially no change in the duration of daylight through the year. Daylight remains constant. Tropical fishes are cued to spawn by other environmental changes such as rainfall or current flows in rivers and streams.

Temp/Day Length Intertwined
Dr. James Tidwell, fisheries’ professor at Kentucky State University, said the two factors, temperature and day length, are inextricable.

“They’re intertwined, light and temperature,” said Tidwell. But Tidwell thinks that day length gets ignored in understanding animal behavior, and that temperature is over emphasized. “The earth follows the same path around the sun every year, and vegetation changes seasonally — and very predictably.”

Here’s something else that may be predictable: as daylight increases, your eye unconsciously catches more light, stimulating your brain to produce hormones that cause you to behave a certain way. You’ll spend more time and money at the tackle shop; you’ll make sure the trailer is good working order, the live well works, and you’ll have a primordial longing to outwit big bass. It comes on like clockwork, every year. You can’t help it, it’s coded in your DNA but you may just have to wait for the synchronicity of a warming water temperature and the right mix of hormones streaming through a bass’s blood to get fish on the feed.

As sure as day follows night, planet Earth will wobble back toward the sun, and higher temperatures will be here soon enough, and streams and lake shores will be dotted with the gravelly dishes fit for one male black bass guarding the nest.

For a fine assortment of fishing gear, click here.

When not penning stories about the outdoors, Craig works in communications for the U.S. Fish and Wildlife Service. He is an outdoors’ columnist for the Albuquerque Journal and ESPN Outdoors, and a frequent contributor to Flyfisher and North American Fisherman magazines. He holds degrees in fisheries and wildlife management from Hocking College and New Mexico State University, and an M.Sc. in fisheries science from the University of New Mexico. He’s a candidate for an M.A. in rhetoric and writing at the University of New Mexico. He writes weekly for


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