The manner and routes of dispersal vary with the species and the ecological conditions. Many fish form “shoals” to avoid predation. “Shoals” is the term used for any group of fish that stays together for social reasons. Shoaling with familiar conspecifics affords the fish an even greater advantage by increasing the benefit for relatives. This promotes the continuation and future spread of an individual’s own genetic information. Drs. Franziska Lemmel-Schädelin, Wouter van Dongen, Yoshan Moodley, and Richard Wagner from the Konrad Lorenz Institute of Ethology studied Neolamprologus caudopunctatus, a species of cichlid fish endemic to Lake Tanganyika, Africa’s second largest and the world’s second deepest freshwater lake. Lake Tanganyika has a surface volume of about 33,000 square meters, which corresponds to the size of Belgium. The researchers studied the influence of sex and size on dispersal and shoaling behavior. Dr. Lemmel-Schädelin and her field assistants carried out a number of dives in October and November 2008 to study the dispersal behaviour and relationships of over 900 cichlids. The divers collected DNA samples from the dorsal fins and documented the body size and sex of the fish. An analysis of the data showed that over the course of their lives the females dispersed farther from their parental nesting sites than males. “To avoid inbreeding and resource competition, it is usual among many animals for one sex to disperse farther from their place of birth than the other. Male-biased dispersal is more frequently the norm among mammals, with females remaining near the original nesting area. Among the cichlids we studied, on the other hand, it appears to be the females that disperse,” says ethologist Dr. Lemmel-Schädelin.
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