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DIAGNOSTIC TEST
Bluegils
Anglers will recognize the bluegill as one of the most popular gaming fish in North America and it
is frequently found in freshwater lakes and ponds. This relatively small fish which rarely reaches
length over 6-9 inches( 15-23cm) has also been the subject of intense study by many wildlife
biologists for its unusual mating habits. While similar to other fish in that the male cares for the
offspring, the alpha males which are larger than the females and other males can never be sure
that it is truly their own fry which they are raising since there are others which try to circumvent the
mating rituals and fertilize the eggs by deception.
2 Comprising roughly 80 percent of the breeding population, large parental males, distinguished
by their size, copper colored bars across the top of their heads behind the eyes, and silvery blue
breasts that may turn yellow or orange during the spawning season, commonly manage bluegil
reproduction. They do not reach sexual maturity until their third or fourth year and this delay allows
them to direct their consumed food resources to developing a large body mass, which is
advantageous for successfully defending their territory and fighting off predators. Because these
fish are colony spawners, adult parental males will excavate plate-sized nests in groups of 20 or
30, called "beddings," by sweeping their tail fins across the sandy floor to make depressions.
Then, in the shallow water, the male circles the nest and makes grunting noises to attract one or
more females. The male guards the newly deposited and fertilized eggs and continues to do so
even after the hatch and the emergence of the fry until they are old enough to survive on their
own.
3 A small proportion - about 20 percent - of bluegill males do not wait until they are large
enough to defend territory before entering the reproductive process. Cuckolds, or sneakers, divert
most of their energy towards their gonads that produce milt, a secretion from their testes
containing spermatozoa; as a result, they have invested in a procreative strategy requiring them to
take advantage of nearby nests. Cuckolds are too meek to successfully attract a female fish on
their own. They seek out a large parental male, hide in the weeds adjacent to the parental male's
breeding grounds, and wait for a school of female fish to pass over. Once a female chooses a
partner, she will tilt her body and release roughly 30 eggs in a motion referred to as a "dip."
Normally, the resident parental male would shower these eggs with his own milt, but before he has
a chance to reach all of them, the diminutive cuckold will leave his safety zone and dart into the
dangerous nest area to squirt his own milt toward the eggs, quickly returning to his point of origin
without being caught. With this tactic, he hopes to fertlize as many of the eggs as possible before
they settle into the hole, and will use his undersized body to advance with utmost agility. It
fortunate enough to complete the task without encountering any significant harm, the cuckold will
go on to stalk other parental male nests over the same season,