Animal Behavior/Reproductive Strategies in Fish

Reproduction is the sole method through which a species may continue, and reproduction manifests itself in numerous deviations throughout nature. The ultimate goal of each species is to produce the maximum amount of offspring while exerting the least amount of energy. Predation pressures, resource accessibility, and competition with the species for attracting mates greatly influence the likelihood of an individual within a species producing viable offspring and donating genes to subsequent generations. Different fish species may be observed in order to learn the unique reproductive strategies employed throughout nature from fertilization tactics to parental care methods that have adapted these fish in continuing their species.

Females typically exert much more energy and time into reproduction than males, and therefore, females are usually more selective in choosing mates. Females typically favor males that are larger in size, possess more elaborate physical traits than the other males, and display more energy in courtship activity.[1] However, smaller and less desirable males must still be able to fertilize the eggs, or, according to natural selection, they would have been eliminated from the population. Although slightly more unsettling, sexual coercion results in the fertilizing of eggs just as sexual courtship does. The term “sneakers” refers to smaller males who opt to race into the nest more desired males and fertilize the eggs while the nesting male pursues the female.[2] The term “satellites” describes cryptic males mimicking females in appearance and behavior so that they are able to fertilize the eggs while the unsuspecting couple spawn.

Although fish species exhibit both internal and external fertilization, fish also exemplify many unique strategies for parental care. Most fish species utilize broadcast spawning, which is a method a releasing gametes into the water and providing no parental care. The goal of this reproductive method is to produce the maximum amount of progeny in hopes that as many offspring as possible will survive. Many fish species, however, opt to employ parental care in order to supply their smaller number of offspring a greater chance of survival. Oral brooding and sex role reversal are two unique methods of parental care that have proved successful in certain fish species.

Oral brooding, although quite rare in nature, is a parenting method adopted by many fish in the Family Cichlidae.[3] After the successful fertilization of the eggs, Cichlids, such as Tilapia, place the egg clutch into the mouth of the female. The fecundity is significantly lower in oral brooders; however, the eggs tend to be larger and receive more nutrients. By placing the eggs into the oral cavity, the female is able to provide protection for the eggs, and the churning ability of the female rotates the eggs so that each egg is exposed to oxygenated water.

Similar to oral brooding, sex role reversal in fish is rare but is utilized in the Family Sygnathildae.[4] In sea horses, the female inseminates the male by inserting the oviduct into the male brooding pouch several times to ensure fertilization. After fertilization is complete, the female departs, and the male attaches itself to a nearby object with its tail waiting for the eggs to mature.

Nature exhibits many alternatives that species have adapted in order to reproduce. By utilizing these methods, these organisms are able to reproduce viable offspring and continue their kind. Survival of the species is the ultimate goal for all organisms, and these organisms are constantly adapting to their environment in order to do so.