Do you know the biology of the spawn?

After the courtship and its culmination, the female swims off, leaving the male to guard the eggs and fry.

The largemouth bass are spawning. In South Mississippi, bass have been bedding for a couple weeks in ponds and in backwaters of the Pascagoula and Pearl rivers. In central Mississippi waters, the spawn is heading toward a peak.

What do biologists know about largemouth bass spawning that may help you better understand the spawning cycle and pinpoint your efforts in likely spawning areas?


Biology basics

Largemouth bass spawn at 64-68 degrees. In almost every lake, some bass will spawn at slightly cooler temperatures, and some at warmer temperatures. While anglers are often quick to contest the 64-68 spawning window, the question that seems to get overlooked is where and when the temperature is measured. Water temperatures vary throughout larger lakes in the spring. Shallow, dark-bottom backwaters and coves warm faster and sooner than the deeper main lake, so it is easy to accept bass spawning in a shallow, protected cove when the main lake temperature is still in the 50s.

Bass seem to “know” where to seek warmer water, but how they know remains a mystery. Possibly the bass learn from prior experience, which might explain why the bigger bass are usually the first fish to move into the shallow spawning areas. The variations in water temperature within a lake probably contribute to the duration of the spawn.

Largemouth bass build nests on hard bottom, usually in water 2 to 4 feet deep. Largemouth will nest deeper in clear water, but reports of largemouth bass nesting 15 to 20 feet deep have not been substantiated by biologists.

The nests can be constructed anywhere, but they tend to be clustered on protected shorelines and areas sheltered from heavy waves or flowing water. Commonly, nests will be adjacent to hard cover, like a stump or a rock, if available. The male places his head in the center of the nest and with powerful movements, sweeps silt and debris out of the nest area. The result is a circular area clear of debris, with a hard bottom, and with a diameter approximately twice the length of the male bass.

The nests tend to be shallower on hard bottoms, deeper on soft bottoms. In lakes with bottoms thickly covered with detritus (partly decomposed plant material), largemouth bass will actually spawn on hard objects above the bottom. I have observed male bass guarding eggs deposited on a spatterdock tuber growing above the bottom in a heavily vegetated Florida lake.

Whether the female finds the male or the male searches for the female and lures her to the nest is not known. At the nest, courtship displays accompanied by vivid color changes and punctuated by the male bass physically contacting and prodding the female stimulates the release of eggs, which are quickly fertilized by milt released by the male. The prodding is not to physically “loosen the eggs” as I have read in several articles.

Several bouts of courtship and release of eggs and milt may occur before the female swims off. Reports vary on whether a female will spawn in multiple nests and whether male bass will try to court several females.

The number of mature eggs a female bass will carry, termed fecundity, ranges upward of 100,000, and is related to the size of the female largemouth. Measures of relative fecundity — the number of eggs divided by the weight of the female bass — vary widely, but a reasonable “general” value is 10,000 eggs per pound of female.

The heavier-than-water eggs settle into the nest, and after spawning is complete, the male guards the eggs. The male positions himself over the nest to watch for would-be egg or fry predators. Fin movements keep water moving over the egg mass to provide fresh, oxygenated water and to keep the eggs from being covered by suffocating sediment. The guarding male does not eat, even though it may capture nest-marauding predators like sunfish or crayfish.

The eggs hatch in two to four days depending on water temperature (incubation is faster in warmer water). The larvae become free swimming in about 10 days, and the yolk sac is completely absorbed shortly after. The weakly swimming larvae have only a few days to begin feeding before their energy reserves are depleted, and a good supply of zooplankton is important to growth and survival of the fry. The fry remain in a dense school, and the adult male will continue to guard the fry school until they grow to about ½-inch long.


Preserving bass populations

I am not aware of any bass fisheries in Mississippi where reproduction is presently limited, but habitat management is still called for. Threats to successful bass spawning in Mississippi waters are loss of hard-bottom spawning areas from sedimentation or the build-up of detritus, especially where water hyacinths flourish.

Anglers have a role, too. Bed fishing is always a hot topic. No largemouth bass population has been shown to be reduced by bed fishing, so decisions about bed fishing are personal issues. However, the science is clear that keeping a caught bass off the nest for several hours or longer is likely to result in no offspring produced in that nest.

By the end of this month, billions of bass fingerlings will have been produced in Mississippi’s waters. Next month I’ll discuss the fates of these fish and steps that can be taken to ensure the production of sufficient numbers of young bass to provide satisfying bass fishing opportunities.


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About Hal Schramm 168 Articles
Hal Schramm is an avid angler and veteran fisheries biologist.

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