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Live and dummy stimulus fishes were used to determine why female convict cichlids, Cichlasoma nigrofasciatum, develop orange ventral coloration. Results show that male cichlids are insensitive to ventral color variation, while females seem to use color pattern as a visual cue. Females tend to be aggressive towards brightly colored fishes, while bright females exhibit the least aggression towards an intruding female of intermediate coloration. The findings indicate that sexual dichromatism in C. nigrofasciatum influences intrasexual aggression among females.

Many critical cellular processes, including cell proliferation and tissue repair, exhibit melatonin sensitivity. We examined the effects of exogenous melatonin, photoperiod and temperature on regeneration in Phagocata gracilis, a common North American turbellarian. Planarian regeneration involves the proliferation and migration of pluripotent stem cells capable of replacing missing body components. A characteristic mass of cells (blastema) forms during planarian regeneration, and its formation, growth and differentiation provide reliable endpoints for the study of regenerative processes. We tested the effects of exogenous melatonin at two concentrations and three photoperiods on both head and tail regenerates under seasonal diurnal temperature regimes. High temperatures and melatonin treatment increased mortality in P. gracilis, and surviving melatonin-treated subjects exhibited delayed regeneration. Asymmetrical and deficient regeneration was more common in melatonin-treated, high temperature and dark treated subjects. Additionally, high temperature and melatonin induced a novel locomotor dysfunction. [ABSTRACT FROM AUTHOR]