Using attraction to light to decrease cannibalism and increase fry production in guppy (Poecilia reticulata Peters) hatcheries. II: the effects of light and cannibalistic adults

Predation of newborn fish by cannibalistic adults is a major cause of fry loss in guppy breeding tanks. The efficacy of using light to attract newborn guppies into a safe area, thereby reducing the cannibalism rate, was evaluated in aquaria. The aquaria were divided using small‐mesh netting into a section with adult fish and a safe section without adults, above which a light source was installed to attract the newborns. Both, the presence of cannibalistic adults and the light, increased the number of newborns in the safe section. The effect of the cannibals was pronounced during the day, and the effect of light seemed to be more pronounced at night. The presence of light significantly decreased cannibalism rate after 30 min, but not 16 h after the introduction of newborns. When tested with cannibalistic adults that have not been fed for 5 days prior to testing, cannibalism rate was higher and the effect of light on reducing cannibalism was evident both 30 min and 16 h after the introduction of newborns. The results demonstrated the potential efficacy of using white light in reducing cannibalism and increasing fry yields in guppy hatcheries.