Polyculture of mixed-sex and male populations of Nile tilapia (Oreochromis niloticus) with the Mayan cichlid (Cichlasoma urophthalmus)

Abstract

The purpose of this study was to test polyculture of Nile tilapia and the native Mayan cichlid, as an alternative production method of tilapia. The experiment had a 2×4 factorial design: the first factor was the population of tilapia (mixed-sex and 95% males) and the second factor was the proportion of Nile tilapia: Mayan cichlid (3:1, 5:1, 7:1 and 1:0). Proportion of 1:0 was tilapia monoculture. At stocking, tilapias were 11weeks old and weighed 24.0g and Mayan cichlids weighed 5.0g. Recirculating water systems were used, with 24 fiberglass tanks 1m3 with permanent water flow (7Lmin−1) and aeration. Each treatment had 3 replicates distributed randomly, and 24 fish were introduced in each tank (30fishm−3). The experiment lasted 21weeks, until tilapia reached marketable size. 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±1.2mgL−1 and 7.9±0.2) were within the appropriate ranges for growth, and TAN, nitrites and total alkalinity (0.29±0.22mgL−1, 0.04±0.03mgL−1 and 238±27mgL−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 (45g 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 (9.26kgm−3, 1.39 and 383g) than in the mixed-sex population (7.70kgm−3, 1.52 and 315g). 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 (45.9g) than in the 95% male population (34.4g). Mayan cichlid growth was inversely proportional to its density, with final weights of 45.5g, 39.0g and 34.3g (7:1>5:1>3:1). The differences in Mayan cichlid growth are associated with intraspecific competition for available tilapia larvae. Mouth brooding tilapia females with eggs or larvae were observed in both tilapia populations and in all proportions. When fish were weighed some tilapia females released their larvae in the tanks, and both Mayan cichlid and tilapia males were observed preying on them.