Trophic spectrum of the cichlids Cichlasoma (Parapetenia) istlanum and Cichlasoma (Arconcentrus) nigrofasciatum in the Amacuzac River, Morelos, Mexico

" I compared the trophic spectrum of Cichlasoma istlanum and C. nigrofasciatum of the Amacuzac, River. The diet of C. istlanum was composed of 13 prey categories, and that C. nigrofasciatum had 26. The niche amplitude index values showed that both species have narrow trophic niches (0.29 for C. istlanum and 0.12 for C. nigrofasciatum). The overlapping index of feeding niche value was 0.50, indicating that the diet for both species was significantly different (X2 = 89.8, P < 0.05). These species shared five food types during the dry season and six during the rainy season. The index of overlap in the rainy season was 0.70. However, chi-square test values indicated that diet was different (X2 = 92.35, P < 0.05). Analysis of the diet by age showed that the young and adults in both species shared three food types. The diets were statistically different (X2 = 91.7, P < 0.05, for young: X2 = 137.74, P < 0.05 for adults). Cichlasoma istlanum is a specialized entomophagous carnivore, and C. nigrofasciatum is an omnivore with a carnivorous tendency. Displacement of C. istlanum by C. nigrofasciatum due to alimentary interference seems unlikely "