Schooling in fish  (Page 7/10)

Sexual schooling

Sexual segregation can be seen in many fish schools. In eastern mosquitofish ( Gambusia holbrooki ) it is costly for females who are foraging to be sexually harassed by males (Bisazza et al 2007), which often happens to solitary females. Therefore, they school with other females when males are in sight, or school with schools of males (who do not sexually harass), staying closest to the largest males (Bisazza et al 2007). In guppies, females form the base of a school, while males tradeoff schooling with the intention of finding mating opportunities. Males cannot search for mates while schooling, as schools either engage in anti-predatory or foraging behavior. Therefore, they must tradeoff between increased motility for mating opportunities and the increased defenses and resources that accompany schooling (Griffiths and Magurran 1998). In high predator areas, females school more, but are harassed more too because males spend less time schooling, foraging, and avoiding predators than females, and more time looking for mates, who are easier to find in groups (Magurran and Seghers 1994). These situations form the crux of the sexual conflict between the sexes: females try to avoid harassment by males through schooling, though this is not the only reason for schooling behavior ( [link] ), while males pursue these schools as opportunities for increased mating potential. The “winner” of the conflict is determined by the strength of the school as well as the threat posed to solitary males, especially in high predator areas. Males increase their fitness by mating more, while females increase their fitness by acquiring resources to support current and future offspring. As such, the threat to males is only significant if it outweighs the benefit of increased mating opportunities. The conflict between males and females can be found in many species, but the use of schools as a defense is an interesting physical manifestation of this evolutionary tug of war to harass and defend.

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Mixed schooling

Mixed schooling is an interesting phenomenon that is observed in a few species. Stoplight parrotfish, striped parrotfish, and ocean surgeonfish will school together, but only the largest constituent uses the school for protection: in the event of a threat the lesser represented species will leave and hide behind coral. A possible explanation for this behavior is that underrepresented fish may stick out and would not be protected within a mixed school (Wolf 1985). Other than the potential for better foraging, no explanation has arisen as to why mixed schooling of this nature occurs. Especially since the school is composed of different species, there is reason to believe that competition would be significantly increased, though this has not been observed. However, the reason for mixed schooling between postlarval French grunts, ( Haemulon flavolineatum ) and mysids is much more obvious. Postlarval French grunts form schools based on visual recognition, and mysides look like grunts up until 5 days. After 5 days, the grunts abandon the mysids as they look different. This is an example of young fish being unable to distinguish between species and mysids going along for the ride so long as they can get food out of the association (Kotchian and MacFarland 1982).