Turnover And Fractionation Of Stable Carbon And Nitrogen Isotopes In Multiple Tissues Of Two Yellow Catfish Species

Stable isotope analysis is widely used in trophic ecology study and has been a powerful tool to examine structure and trophic interactions of aquatic food webs. Multiple tissues of organisms may provide diet information of their life history. Stable isotope turnover rate is the speed at which a fish will reach equilibrium after a shift to isotopically distinct prey, which is contributed by both metabolism and growth factor. The fractionation factor including the enrichment of stable isotope and different distribution of stable isotope in different tissues. The turnover rates of different tissues may reflect the dietary habit of several time periods. Applications on reconstruction of diet and migration patterns require precise estimates of turnover rate and discrimination factor of each isotope in the studying tissues. Recently, with the development of aquaculture, the diet of yellow catfish Pelteobagrus fulvidraco draw more and more attention from researchers. Yellow catfish is omnivorous fish and plays an important role in the freshwater ecosystems. With the individual growth, increasing the diameter, the diet it ingestion also changed through its life history.We simulated the diet shift by changing the food source of yellow catfish under control experiment to investigate different of stable carbon and nitrogen isotope turnover rates of different tissues, to analysis the contribution rate of growth and metabolism factor to stable isotope turnover rates and estimate the fractionation factor of different tissues of yellow catfish. Results showed that:（1） Mucus and liver of catfish have the highest turnover rates, the stable isotope turnover rates of fin, muscle and gill are relatively slow. The turnover rates of tissues are: mucus(δ¹³C: 28.0d, δ¹⁵N: 35.7d) and liver(δ¹³C: 25.8 d, δ¹⁵N: 63.6d), fin(δ¹³C: 106.5 d, δ¹⁵N: 64.2d), gill(δ¹³C: 196.9 d, δ¹⁵N: 196.8d) and muscle(δ¹³C: 92.6d), respectively.（2） The stable carbon and nitrogen isotope discrimination factors are variable in tissues. Discrimination factors of tissues ranged from-2.1‰ to 2.0‰ for carbon and-1.4‰ to 2.4‰ for nitrogen.（3） Metabolism accounts for more than 60% of δ¹³C and δ¹⁵N in all tissues except for gill.（4） The variation in turnover rates of multiple tissues may provide complementary information for diet reconstruction at different time scales, the mucus and liver may reflect short time diet shift, while fin, liver and muscle may reflect a longer period of dietary information.（5） The relationship of body length and weight of P. nitidus in Dianshan Lake is W=0.0192×BL^2.7766, R2=0.78. The function shows that of P. nitidus has an allometric growth pattern（b<3）.（6） The correlation analysis of liver and gill δ¹³C and δ¹⁵N values show that there is only δ¹⁵N of gill and body length significant correlation. P. nitidus’ s diet keep stable after the length reach 8cm, and the δ¹³C of liver and gill is in equilibrium, and the increasing rate of δ¹⁵N of liver and gill is very slow. There is no significant relationship between deviation of liver and gill δ¹³C（Δ13Cliver-gil） and body length, and the value>0.（7） The trophic position of P. nitidus of Dianshan Lake estimate through liver is 3.50,and through gill is 2.86,which means liver reflect P. nitidus short-term dietary information, while gill reflect the long-term dietary information. It’s possible to study the dietary information and trophic relationship of different time scale from multiple tissues of the same individual. P. nitidus diet derived from both plankton and benthic food sources.