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Dominance hierarchies are generally established based on the levels of aggressiveness that animals present. Frequently, animals fight to establish a dominance hierarchy and obtain a disputed resource. The Mexican mojarra Cichlasoma istlanum is a native species of the Balsas river basin and coexists there with four nonnative cichlids: tilapia Oreochromis sp., convict cichlid Amatitlania nigrofasciata, spotcheek cichlid Thorichthys maculipinnis, and green terror Andinoacara rivulatus. These five cichlid species compete for spaces for reproduction, feeding, and shelter and frequently engage in aggressive interactions to obtain these resources. We quantified dominance indices to evaluate the hierarchical structure of dominance among these five cichlids and the duration of aggressive behaviors of the Mexican mojarra during experimental contests between the native species and each of the four nonnative species. The Mexican mojarra was consistently dominant over the other four cichlid

Colour production in fish is due mostly to food. In conditions of captivity, the type of food is restricted, while various types of food are used in aquaculture, from processed dry food to small aquatic animals. In this study, we used nauplii of Artemia franciscana, "water fleas" Moina wierzejski, micro-worm Panagrellus redivivus, and commercial flakes. We used Poecilia reticulata, which is one of the most traded fish in ornamental aquaculture and hypothesise that if the live food influences the coloration and growth of P. reticulata, there must be differences in the intensity of colour pattern and growth rate in fish fed with different living animals. Consistent with our prediction, females and males of P. reticulata were more colourful when they were fed on A. franciscana, P. redivivus and M. wierzejski than when they were fed commercial flakes. Females and males of P. reticulata fed with A. franciscana grew in less time than fish fed with P. redivivus, M. wierzejski, or commercial flakes. We conclude that live food is an excellent way to affect growth and coloration in fish.

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