Effects Of Straw Returning And Feed Addition On The Food Source Of Crayfish And The Diversity Of Aquatic Organisms In The Rice-Crayfish Co-Culture System

Rice-crayfish co-culture,as a new type of rice field farming model that combines rice planting and crayfish farming,has been widely promoted in China in recent years due to its high economic benefits.Straw return to the field and feeding crayfish are two important measures for crayfish farming in rice fields,which can directly or indirectly provide food sources for crayfish.In order to fully utilize the biological resources of rice paddies,meet the food source for crayfish farming in rice paddies,and improve the utilization efficiency of rice straw and feeding,this study conducted a straw feed experiment in Rice-crayfish co-culture from 2021 to 2022.Four experimental treatments were set up,namely: straw with feed(SF),straw with no feed(SNF),no straw with feed(NSF),and no straw with no feed(NSNF),The carbon and nitrogen stable isotope values of crayfish and its food sources were measured,and the contribution rates of each food source were calculated through MIXSIAR analysis to clarify the impact of straw returning and feeding on crayfish food sources.The results were confirmed by the 2022 biodiversity analysis of phytoplankton,zooplankton,and benthic animals.The main research findings are as follows:(1)The analysis of crayfish yield between different treatments showed that from2021 to 2022,straw return to the field and feeding significantly increased the yield of crayfish,and in 2022,straw return to the field and feeding increased the yield of crayfish,respectively.The yield of crayfish is 67.4%.Compared with the four treatments,the yield of crayfish was in the order of SF>NSF>SNF>NSNF.In 2022,SF significantly increased the yield of crayfish by 75% compared to NSNF.(2)The food source analysis of crayfish between different treatments showed that using carbon and nitrogen stable isotope techniques to analyze the food source of crayfish in the Rice-crayfish co-culture system showed that the changes in the food source of crayfish were basically the same in the two years from 2021 to 2022.The impact of straw and feeding on crayfish was relatively small in March.In 2022,the proportion of natural feed in SF,SNF,NSNF,and NSF was 89.3%,94.9%,and 92.6% and 100%,respectively.In SF and SNF,the proportion of straw as a source of food was 4.8% and 5.2%,respectively;The proportion of feed sources in SF and NSF was 6% and 7.4%,respectively.The first source of food for crayfish in the treatment room was organic debris(POM).Straw return to the field reduced the contribution rate of POM and phytoplankton to the food source by 6.5% and 34%,respectively;Effectively increased the feed source contribution rates of zooplankton and aquatic plants by 32.7% and 27.3%,respectively.Feeding effectively reduced the food source contribution rates of POM and aquatic plants by 29.6% and 84.5%,respectively;Effectively increased the feed source contribution rates of zooplankton and aquatic plants by 151% and 140%,respectively.The contribution rate of food sources in SF in 2022 was in the order of POM>phytoplankton>zooplankton>feed>aquatic plants>straw.From May 2021 to 2022,the feeding ability of crayfish increased,and the proportion of straw and feed intake increased.Compared with March,the proportion of natural feed sources in each treatment significantly decreased.In 2022,the proportion of natural feed in SF,SNF,NSF,and NSNF was 70.5%,82%,77.6% and 100%,respectively.In SF and SNF,the proportion of straw sources is 13.3% and 18% respectively;In SF and NSF,the proportion of feed sources is 16.1% and 22.4%,respectively.Straw return to the field reduced the contribution rates of POM,aquatic plants,and zooplankton by 9.7%,15.7%,and 50.5%,respectively.Feeding significantly reduced the contribution rates of POM,aquatic plants,zooplankton,and phytoplankton by 44.2%,16.7%,2.3%,and 8.3%.The contribution rate of food sources in SF was in the order of POM>zooplankton>feed>phytoplankton>aquatic plants>straw.(3)The diversity analysis of phytoplankton between different treatments showed that in 2021,there were a total of 8 phyla and 65 genera of phytoplankton in all treatments,including 14 genera of Cyanophyta,28 genera of Chlorophyta,6 genera of Bacillariophyta,7 genera of Euglenophyta,2 genera of Cryptophyta,3 genera of Euglenophyt,3 genera of Pyrrophyta and 1 genera of Xanthophyta.The dominant species were Cyanophyta and Chlorophyta.There was no significant difference between different treatments.Straw return to the field increased the density of phytoplankton by 9.5%;Feeding significantly reduced the density of phytoplankton by 37%.The density of phytoplankton among different treatments is in the order of SNF>NSNF>SF>NSF.Straw return to the field could significantly increase the biomass of phytoplankton by 133.6%.Feeding significantly reduced the biomass of phytoplankton by 37.1%,The order of biomass of phytoplankton among different treatments is: SNF>SF>NSNF>NSF.The effects of straw returning and feeding on the biodiversity index,evenness,and richness index of phytoplankton were not significant.(4)The diversity analysis of zooplankton between different treatments showed that there were a total of 4 phyla,53 genera,and 93 species of zooplankton,including 47 species of rotifers,37 species of Primitive,5 species of Copepods,and 4 species of Cladocera.The dominant species were rotifers and primitive,and the differences between treatments are not significant.Straw return to the field significantly reduced the density of zooplankton by 41.2% and 53.0%,respectively.The density of zooplankton among different treatments was as follows: NSNF>SF>SNF>NSF.Straw return to the field significantly increased the biomass of zooplankton by 65.3%,while feeding significantly reduced the biomass of zooplankton by 47.8%.The biomass of zooplankton among different treatments was in the following order: SNF>NSNF>SF>NSF.The effects of straw return to the field and feeding on the biodiversity index,evenness,and richness index of zooplankton were not significant.(5)The diversity analysis of benthos in different treatments showed that the benthos in the four treatments were basically annelids,belonging to 3 phyla and 8 genera in total,and the dominant genera were mainly Annelida,Arthropoda,and Mollusca.Compared to the no feeding treatment,feeding significantly increased the density of benthic animals by78%.The density of benthic animals among different treatments is as follows:NSF>NSNF>SNF>SF.Straw return to the field and feeding increased the biomass of benthos by 293% and 229% respectively.The order of benthic animal biomass among different treatments was: SNF>NSF>NSNF>SF.Straw return and feeding did not have a significant impact on the biodiversity index,evenness index,and richness index of benthic animals.In summary,straw return to the field and feeding are beneficial for the stability of the water environment in rice paddies.While increasing the yield of crayfish,there is no significant negative impact on the water environment in the rice paddies.Straw return to the field and feeding have an impact on the proportion of crayfish food sources.It is recommended to regulate the feed feeding amount at different stages of aquaculture to avoid resource waste.