Fish were fed with extruded formulated diets for tilapia (40% and 30% crude protein).
Daily feeding rate was restricted to between 4% and 1.8% of the fish biomass. Temperature, DO and pH
(28.0 ± 1.1 °C, 5.2 ± 1.2 mg L−1 and 7.9 ± 0.2) were within the appropriate ranges for growth, and
TAN, nitrites and total alkalinity (0.29 ± 0.22 mg L−1, 0.04 ± 0.03 mg L−1 and 238 ± 27 mg L−1) were
within safe ranges. Average survival was high (99%) and no differences were found between populations
and among proportions. Nile tilapia Stirling strain showed early (45 g after 3 experimental weeks) sexual
maturation and growth dimorphism. Significantly better total yield, FCR and final tilapia body weight were
obtained in the 95% male population (9.26 kg m−3, 1.39 and 383 g) than in the mixed-sex population
(7.70 kg m−3, 1.52 and 315 g). The presence of the Mayan cichlid did not affect tilapia performance. The final
weight of Mayan cichlid was significantly higher in the mixed-sex tilapia population (45.9 g) than in the 95%
male population (34.4 g). Mayan cichlid growth was inversely proportional to its density, with final weights of
45.5 g, 39.0 g and 34.3 g (7:1 N 5:1 N 3:1). The differences inMayan cichlid growth are associatedwith intraspecific
competition for available tilapia larvae.Mouth brooding tilapia femaleswith eggs or larvae were observed in
both tilapia populations and in all proportions.When fishwereweighed some tilapia females released their larvae
in the tanks, and both Mayan cichlid and tilapia males were observed preying on them.