Biology of the Bass Spawn
written by Wade Bourne

 
When, where, and how America's favorite gamefish spawns.
 
 spring pond bass

 The clearer the water, the deeper bass build their nests.  

The spawning cycle of largemouth bass is a unique, highly complex ritual that ensures this species' regeneration from one year to the next.  Following is a look at when, where and how these fish spawn as related by Marty Mann, a fisheries biologist with the Florida Game and Fresh Water Fish Commission.  The following information is specific to Florida waters, though the bass' spawning ritual is fairly standard from one region to the next.
 

Two factors determine when bass spawn:  photo period (length of daylight) and water temperature.  The latter factor is most important.  When water temperature climbs into the low 60s, spawning activity begins, and it continues until the water reaches 80 degrees.  Most spawning activity occurs in the 65-70 degree range.

There is much conjecture over what role moon phase plays in the initiation of spawning.  Many laymen believe most bass spawn around the full and new moons, though this has not been substantiated scientifically.

When the water temperature is right, male bass move into the shallows to pick their nest sites.  Frequently these fish fight over choice spots.  Larger males are more aggressive and typically claim the best sites.
 

These males establish their nests in water from a few inches deep up to 10 feet, depending on water clarity (the clearer the water, the deeper the nests).  Predominant depths of spawning nests are 2-4 feet.

The best sites are those with sand or gravel bottoms and with vegetation or some other object (log, stump) at hand.  Fertilized eggs are sticky, and they cling better to clean, textured bottoms, lessening the chance that they will be swept away by wave action.  Also, vegetation and other features provide some protection from waves.

 bass bed

Beds are formed when a buck bass sweeps silt away with his tail.  He anchors his nose in the center of the nest, then pivots around to sweep a full circle.  

When he chooses a nest site, a male bass will begin sweeping silt away with his tail.  He will anchor his nose in the center of the nest, then pivot around to sweep a full circle.  Thus, the radius of a nest is the same approximate length as the male's body.
 

Next, egg-laden females enter the spawning area.  When a male bass sees an available female, he attempts to corral and herd her to the nest.  This behavior is accompanied by rapid color pattern changes to attract her attention.  Frequently there is heated competition for a female between two or more males.

Once a male and female are paired off on a nest, egg-laying and fertilizing begins.  This is preceded by a display and touching ritual of varying lengths.  Then, when she's ready, the female shudders and forces eggs out through her vent.  The male simultaneously secretes semen, which mixes with the eggs in the water to fertilize them.  Then the eggs settle to the bottom of the nest.  Egg-laying and fertilization will last a half hour and include up to six egg release/fertilization sequences.

The female leaves the nest shortly after dropping her eggs.  Then she will mate with another male and spawn again.  A female will mate with up to five different males per season.  This is nature's way of ensuring a genetic mix and a better chance that at least some of the female's eggs will survive to hatch out.

After the female leaves the nest, the male will begin fanning the eggs with his tail to oxygenate them and to keep silt from covering them.  During this fanning period, if another ripe female swims by, the male will attempt to herd her to his nest for another spawning effort.  Just as females may mate with multiple males, a male guarding a nest may mate with 3-4 females in a short time frame, with the eggs from the different sows mixing together in the nest.

Hatching comes 48-72 hours after the eggs are laid, depending on water temperature (the warmer the water, the shorter time until hatching).  The fry will hover over the nest a day or two, then they will disperse.  When the fry leave, the male abandons the nest, and his role in the spawning cycle is over until the next spring.

Several natural conditions can lower spawning success.  One of the most detrimental is back-to-back cold fronts, which can lower water temperature and kill newly hatched fry.  (A drop in water temperature into the high 50s is enough to kill fry.)  Also, waves from strong winds will blow eggs from exposed nests, thereby diminishing spawning success.