Abstract: In this study, two polyculture modes of grass carp (i.e., polyculture of mud carp and grass carp named as “mud-grass mode” and polyculture of crucian carp and grass carp named as “crucian-grass mode”) were simulated, and the niche width, niche overlap, and specific growth rate of grass carp as well as the physical and chemical indices of water under the two polyculture modes were analyzed. There was no significant difference in the niche width of grass carp between the two modes, but the niche overlap of grass carp was significantly different, with the value being 0.5598 and 0.6478 in “mud-grass mode” and “crucian-grass mode”, respectively. The specific growth rate of grass carp in mud-grass mode was 1.524% per day, which was much higher than that (1.346% per day) in crucian-grass mode. The water NH⁺₄-N, NO^-₃, TN, TP, and reactive phosphate contents in mud-grass mode were higher than those in crucian-grass mode, while the water pH value and DO, NO^-₂, and chlorophyll-a contents were in adverse. These results suggested that the competition between crucian carp and grass carp was more severe than that of mud carp and grass carp, and mud carp was more suitable for grass carp than crucian carp in the polyculture.

Key words: Maize aphids, Niche breadth, Niche overlap, Rhopalosiphum maidis Fitch