Bluegill Reproductive Behavior

Bluegills have an interesting and elaborate reproductive behavior. Usually at a spring water temperature around 67^oF, male bluegills will move into shallow water to build nests. Circular nests are created when the male excavating soft bottom materials with their caudal fin (i.e., tail). The nests vary in size but are typically 12-16 inches in diameter and 2-6 inches deep. The completed nest looks like a moon crater. Bluegills spawn in colonies with 20-50 nests found in any one area.

After the nest is constructed females will approach the area and males will attempt to attract them to the nest by repeatedly circling the outside edge of the nest (see video below). This behavior has been termed "rim circling." When a female is attracted both fish will circle the nest before resting at right angles to each other with the female releasing eggs and the male releasing milt. Females may deposit eggs in more than one nest and, consequently, one nest may contain eggs from more than one female.

0:54, 2.8 mb	0:38, 2.0 mb
A bluegill "rimming" the nest.	Another bluegill "rimming" the nest.

When a female has been attracted to the nest both fish will circle the nest before resting at right angles to each other with the female releasing eggs and the male releasing milt. Females may deposit eggs in more than one nest and, consequently, one nest may contain eggs from more than one female.

1:12, 3.8 mb
Male and female spawning.

Females release about 15000 eggs before leaving the nest after spawning. Males, however, will remain on the nest fanning the nest to maintain aeration for the eggs and keeping them free of settled debris. The male must also protect the nest the eggs and young fry from predators (see video below). The most common predators are conspecifics and bullheads.

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Aggressive defense of the nest.	The stare down.

Fry generally hatch in 2-5 days, remaining on the nest until the yolk sac is absorbed and exogenous feeding begins (see video below). Males will guard the nest during the iniital days of the young's life before dispersing.

0:17, 2.1 mb
Nest with hatching fry.

Other Observations

I am not sure what these two bluegills are doing in this video. It seems that they are either (1) feeding or (2) removing material from the nests.

0:43, 2.3 mb
Not sure what is going on here.

Alternative Strategies

Male bluegills have at least three reproductive strategies. The first strategy is demonstrated by so-called "parental males" and is the strategy documented above.

The second strategy is demonstrated by "cuckolders" or "sneakers." This strategy consists of these males maturing at an early age and small size. These males generally do not attract females (because of their small size) and spread their sperm by darting into nests where a parental male and female are extruding gametes. The idea is to fertilize some of the eggs before the larger parental male notices and chases the sneaker male out of the nest.

The third strategy consists of cuckold males that mimic females. In this strategy, the female mimic will approach the opposite side of a female matring with a parental male. The female mimic will again release milt while the parental male and female are extruding gametes. The parental male does not chase away the female mimic -- likely because of the female coloration.

Links

• Bluegill Nesting -- Pond Boss article by Dr. David Willis
• The Secret Life of Bluegill -- Pond Boss article by Dr. David Willis
• Abstract -- Predation and the evolution of colonial nesting in bluegill sunfish (Lepomis macrochirus)
• Abstract -- Habitat characteristics at bluegill spawning colonies in a South Dakota glacial lake
• Abstract -- A Field Study of Nesting Behavior of Male Bluegill Sunfish (Lepomis macrochirus Rafinesque)
• Abstract -- Alternative Male Life Histories in Bluegill Sunfish
• Abstract -- Male size and mating tactic influence proximity to females during sperm competition in bluegill sunfish

Caveats

The videos above are fairly low quality to save space and reduce download time.