| The rice-crayfish coculture system,as one of the main modes of Procambarus clarkii(crayfish),has become the typical culture pattern in the middle and lower reaches of the Yangtze River in China.Fertilization is an essential key link in rice-crayfish coculture systems,which can effectively increase the growth rate and biomass of primary producers in the water,improve the breeding environment,and supplement the growth of crayfish with the necessary trace elements to achieve a win-win situation for both economic and ecological benefits.However,researches on the quality and diet of crayfish after fertilization and the differences in food web structure in rice-shrimp co-cropping systems are still relatively weak.Therefore,four fertilization patterns(no fertilizer,slow-release fertilizer,shrimp rice fertilizer and compound fertilizer)were set up in this study to investigate the differences in the quality and feeding habits of crayfish in different fertilization patterns and the effects on the food web structure of the rice-crayfish coculture system.The nutrient contents and quality of crayfish were comprehensively evaluated by comparing the differences in conventional nutrient contents(moisture,ash,soluble protein and crude fat)and quality(sensory and physical properties)of crayfish under different fertilization patterns.To quantify the differences in food composition and spatial utilization of crayfish,the carbon and nitrogen stable isotope values of crayfish and their potential food sources under different fertilization patterns were measured,and the carbon contributions of their potential food sources to crayfish were output using a Bayesian mixture model.Furthermore,the trophic levels of each consumer in the rice-crayfish coculture system under different fertilization patterns were calculated,and the differences in food web structure of different fertilization patterns were explored using the trophic niche.This research aims to explore the effects of fertilization patterns on crayfish quality and food composition in rice-crayfish coculture systems,and the nutritional structure and energy flow of the biological community in the rice-crayfish coculture system were preliminarily explored.Our results could provide some data support for high-quality crayfish culture,the selection of fertilization patterns in rice-crayfish coculture systems,and the selection of feed for crayfish.The main findings and conclusions are as follows:(1)Comparative analysis of the conventional nutrient composition of crayfish with different fertilization patterns showed that the soluble protein content of crayfish in the no fertilization group was significantly higher than that of the other three fertilized groups,but there were no significant differences in their moisture,ash and crude fat content.The comparative analysis of the muscle quality of crayfish with different fertilization patterns showed that the chela length,breastplate length,body length,fresh weight and dry weight of crayfish with slow-release fertilization were significantly higher than those of the other three groups.The color of crayfish muscle and carapace after the application of shrimp rice fertilizer was obviously different from that of the other three groups.The color of crayfish muscle and carapace was significantly different from those of the other three groups with the application of shrimp rice treasure fertilizer,and the fatness,stickiness and chewiness of shrimp meat with the application of compound fertilizer were significantly lower than those of the other three groups,but the physical properties of crayfish with different fertilization patterns(p H,thylakoid)were significantly higher than those of the other three groups.The physical properties(p H,tethering force and shear force)of crayfish were not significantly different from those of the other three groups.The condition factor,gumminess and chewiness of crayfish muscle were significantly lower after the application of compound fertilizer than in the other three groups,but there were no significant differences in physical properties(p H,water holding capacity and shear force)between fertilization patterns of crayfish.(2)In the rice-crayfish coculture system,the food composition of crayfish in the no fertilizer group was relatively balanced,and its main food sources were angiosperms(Oryza sativa and Cynodon dactylon),particulate organic matter(POM)and artificial feed,with contributions of 23.33%,19.05%,28.54% and 26.28%,respectively.All three fertilization patterns increased the contribution of POM to the diet of crayfish.Meanwhile,crayfish mainly fed on artificial feeds with a contribution of 45.94% in the slow-release fertilizer group,while crayfish mainly fed on POM with a contribution of 56.89% and 42.86% in the shrimp rice fertilizer and compound fertilizer groups,respectively.The SIBER output showed that the isotope niche of crayfish shifted upward in the slow-release fertilizer group.The ecological space utilization of crayfish under different fertilization patterns was compound fertilizer >no fertilizer > shrimp rice treasure fertilizer > slow-release fertilizer.(3)The analysis of the food web structure characteristics of the rice-crayfish coculture system under different fertilization patterns showed that the food chain length in the nonfertilized group was greater than that in the other fertilized groups,but the food diversity,nutrient structure diversity and even distribution of the food web in the rice-crayfish coculture system increased after fertilization.In addition,there was an overlapping trophic niche of different species and a more complex food web structure in the rice-crayfish coculture system in the slow-release fertilizer group,but the trophic niches of the main consumers in the other three groups of rice-crayfish coculture systems did not overlap. |
