Resources In Rice Field Foraged By Aquatic Animals By Means Of Stable Isotopes Analysis

Global agriculture currently faces the challenge of how to produce enough food for the world population with limited land and water resources while not negatively impact environment. As rice field offers a suitable condition for ’fish’ (’fish’, in the thesis refer a wide range of aquatic animals, e.g. crab, carp, shrimp), rice-’fish’ system, integrated rice with freshwater aquaculture, has been under attention. It is well documented that rice-’fish’ system can produce diverse food (rice grain and aquatic protein) by optimizing the benefits of scarce land and water resources, at the meanwhile decreases chemical fertilizers and pesticides use. Rice fields also habitat several kinds of aquatic organisms that can be foraged by fish. However, how fish uses these living resources is less known. Stable isotope analysis (SIA) is widely used in tracing pathways of organic matter (particularly carbon and nitrogen) in food webs, and in determining the contributions of various food items to organisms’diets. SIA is based on assimilated food sources, and provides information on the long-term diets of organisms. Thus, SIA is employed in my study. I first determine carbon (C) and nitrogen (N) discrimination factors by the meta-analysis with the published papers in 2008-2014. I then used the discrimination factors of 13C and 15N to analyze the food sources of three aquatic animals by field experiment. I also analyzed the differences of stable isotope of three genotypes of a common carp originated from rice field. The results are as follows:1A meta-analysis for discrimination factors of carbon and nitrogenA meta-analysis of 31 research papers published within 2008-2014 indicated that the discrimination factors of 13C and 15N significantly differed among arthropods, reptiles, fish and bivalves. The values of discrimination factors of 13C (△13C) and 15N (△15N) are 0.9298-1.2147%o, and 2.5127-2.9987%o respectively.2 The diets analysis of aquatic animals in the three rice-’fish’systemsFood sources of carp, soft-shell turtle and crab in rice-carp system, rice-turtle system and rice-crab system were analyzed by SIA of 13C and 15N. Results showed that diets of carp, soft-shell turtle and crab were from both input feed and natural food s in field. For carp,66.46% of total diets were from input feed and 33.54% were from rice field. For turtle,62.0% of total diets were from input feed, and 38.0% were from rice field. For crab,63.8% of total diets were from input feed, and 36.2% were from rice field.3 Analysis the difference in stable isotopes and diets for the indigenous populationSIA of 13C and 15N was used to test the differences of an indigenous carp (Cyprinus carpio var. color) originated from different locations and from different farms. Results indicated that values of δ15N and δ13C were different between locations, and between farms (intensive farming or traditional farming), suggesting that SIA can be used to identify the origination of this carp.Results by SIA of 13C and 15N also showed that the three genotypes (Red, Black and Red-Black) differed in δ15N and δ13C. For the genotype "Red", the range of 815N and δ13C were 5.022～5.935‰and -25.115～-24.172‰respectively. For the genotype "Black", the range of δ15N and δ13C were 6.651～8.451‰ oand -25.032～-23.707‰ respectively. For the genotype "Red-Black", the range of δ13N and δ13C were 5.395 6.477‰ and-23.39～-21.698‰ respectively.Although there were no significantly difference in the morphology and growth rate in these genotypes, their food sources were different. Foods from input-feed were 66.4% ("Red"),62.5% ("Black") and 65.4% ("Red-Black") respectively under the feeding condition. Under without feed input, genotypes "Red" and "Red-Black" preferred zoobenthos (33.1%,22.6%)、macro-algae (23.2%,37.8%) and duckweed (28.7%, 18.6%), while genotype "Black" preferred zoobenthos (20.1%)、macro-algae (18.9%)、 snails (20.3%)...