Quantitative analysis of density dependent resource utilization, cannibalism, and competition of the red swamp crayfish (Procambarus clarkii) in rice-crayfish cocultures without supplementary food

Abstract

A 90-day, integrated rice-crayfish coculture experiment using net enclosures (8 m × 10 m each) was performed to determine resource utilization, cannibalism, and inter-sexual competition in the red swamp crayfish (Procambarus clarkii) at four stocking densities (4 ind/m2, 6 ind/m2, 9 ind/m2, and 12 ind/m2). The results were as follows: (1) With increasing stocking density of crayfish, the relative contribution of animal feed sources to male and female crayfish diets initially decreased and then increased, whereas the contributions of plant feed sources and detritus as a feed source initially increased and then decreased. There was no significant difference in the diets of female and male crayfish between 4 ind/m2 and 12 ind/m2; plants (> 50%) were predominant, followed by animal feed (> 20%), cannibalism (~ 18%), and detritus (> 6%). At 6 ind/m2 and 9 ind/m2, the contributions of feed sources for both male and female diets were as follows: plants (> 60%), animal feed (> 15%), detritus (> 10%), and cannibalism (< 8%). The trophic and spatial niche area per individual unit (SEA/density, SEA·m2/ind) of female and male crayfish decreased as stocking density increased. (2) With increasing stocking density, the contribution of cannibalized feed sources to crayfish initially decreased (from 4 ind/m2 to 6 ind/m2) and then increased (from 6 ind/m2 to 12 ind/m2). The SEA f,m (representing the similarity of diets between female and male crayfish and, therefore, the potential for inter-sexual competition) initially increased with stocking density (from 4 ind/m2 to 9 ind/m2) and then decreased (from 9 ind/m2 to 12 ind/m2). This indicated that cannibalism might reduce the competition between sexes for natural resources. (3) Based on the high trophic and spatial niche area per individual unit (SEA·m2/ind; female = 0.37 and male = 0.88), low contributions of cannibalized feed sources (female = 5.88 ± 2.62% and male = 7.97 ± 3.44%), and low degree of inter-sexual competition (SEA f,m = 0.25), 6 ind/m2 (crayfish tail weight 9.60 g) was identified as the optimal stocking density for P. clarkii in rice fields without supplementary artificial feed.