Environ Biol Fish (2015) 98:1965–1978 DOI 10.1007/s10641-015-0414-4 Diet of Leptobotia elongata revealed by stomach content analysis and inferred from stable isotope signatures L. Li & Q. Wei Wei & J. Ming Wu & H. Zhang & Y. Liu & X. Xie Received: 4 July 2014 /Accepted: 16 April 2015 /Published online: 8 May 2015 # Springer Science+Business Media Dordrecht 2015 Abstract The diet of Leptobotia elongata in the Yibin shift to piscivory at c.110 mm standard length was found reach of the Yangtze River, China was investigated by using the stable isotope mixing model to reveal dietary stomach content analysis and by stable isotope analysis ontogeny by IsoSource software, and the trend in varia- from muscle. The results of the two methods were agree- tion of the δ13Candδ15N was similar with increased ment. Both stomach contents and isotope analysis indi- body length, and the plankton is important prey item in cated that L. elongata fedinspringmainlyonplankton, all size classes. The δ13Candδ15Nvaluesinsimilar shrimp and fish, and secondarily on benthic invertebrates sized individuals showed significant seasonal differences and aquatic insect larvae. For the stomach content anal- (δ13C, ANOVA, F=76.33,p<0.001 and δ15N, ANOVA, ysis, the diet composition showed significant differences F=144.56, p<0.001), indicating a temporal dietary and among the size classes in relative weight of prey items, trophic level shift. L. elongata is an important commer- with L. elongata changing feeding habits at c.110 mm cial species, and the results of the study form part of a standard length. The smaller individuals fed on benthic detailed investigation of feeding ecology of L. elongata invertebrates and aquatic insect larvae, whereas individ- that provides basic data for studying the food web of the uals >109 mm fed mainly on shrimp and fish. A similar upper Yangtze River. Keywords Leptobotia elongata . Dietary shift . Body length . Season . Stomach contents . Stable isotope L. Li : Q. W. Wei (*) : Y. Li u College of Fishery, Huazhong Agricultural University, Wuhan, Hubei, China e-mail: [email protected] Introduction L. Li : Q. W. Wei : J. M. Wu Key Laboratory of Freshwater Biodiversity Conservation, Leptobotia elongata is a benthic freshwater fish endem- Ministry of Agriculture of China. Yangtze River Fisheries ic in the upper reaches of the Yangtze River, China Research Institute, Chinese Academy of Fishery Sciences, (Anonymous 1976;Chen1980;Liang2000). It is the Wuhan, Hubei, China largest species of Cobitidae in the world, reaching to ’ X. Xie 3kg(Ding1994), mainly inhabiting the river smiddle School of Life Sciences, Southwest University, Beibei, stretch (Ku 1999). In recent years, L. elongata popula- Chongqing, China tions have declined greatly due over-fishing and to environmental deterioration, including the destruction H. Zhang Institute of Geographic Sciences and Natural Resources of spawning grounds and prey (Le and Chen 1998; Research, Chinese Academy of Sciences, Beijing, China Sun et al. 2010). L. elongata was classified as a 1966 Environ Biol Fish (2015) 98:1965–1978 vulnerable species by the Endangered Species Scientific topography, and climate, with up to 286 fish spe- Commission in China in 1998 (Le and Chen 1998). The cies. Construction of the Three Gorges Dam cre- annual catch was 10 000 kg prior to the 2000s, but has ated a reservoir in a stretch of approximately decreased to no more than 2000–3000 kg per year in 600 km from Yichang to Chongqing. The recent years (Duan et al. 2008). L. elongata is an im- National Nature Reserve for rare and endemic fish portant commercial species in the Yibin reach of the species in the upper reaches of the Yangtze River upper Yangtze River in spring, but difficult to catch in was established in 2005 and includes the main other seasons (Li et al. 2013). It has considerable orna- stream of the Yangtze between Xiangjiaba Dam mental value. Recovery of L. elongate populations re- and Masngxi Bridge at Chongqing (approximately quires augmentation of stock through release of fish into 387 km) (Wei 2012). Annual mean air temperature the upper Yangtze River. A stocking program has been is 18 °C, and a flood period extends from June in place since 2010, supported by the China Three through October (Wei 2012). The present study Gorges Corporation, the largest water conservation and was conducted from Nanguang to Nanxi reach in hydropower facility in China. Yibin reach (28°45’ 50^ to 28°48’17^N, Dietary shifts are a common phenomenon of the early 104°39’35^ to 104°57’11^E), located below the life of many fish species (Eloranta et al. 2010)andare junction of the Jinshajiang and Minjiang Rivers usually the result of morphologic constraints, migration, in the central area of the reserve (Fig. 1), which or change in habitat (Grey 2001). Thus far, most studies includes spawning grounds of L. elongata (Zhao of L. elongata have concentrated on its taxonomy and 1995). And L. elongata is an important commer- reproductive biology. Information regarding the feeding cial fish in Yibin reach, representing 3.16 % of strategies of the species, particularlyintheYibinreachof fish harvested annually and 9.53 % of the annual the Yangtze, is scarce. Studies of L. elongata conducted harvest by weight (Li et al. 2013). in the Yichang reach in 1999 used percent frequency of occurrence in stomach content to evaluate ontogenetic Sample collection shifts in diet (Ku 1999). The distance from Yibin reach to Yichang reach is approximately 1040 km. Research on A total of 427L. elongata specimens were collect- the dietary shifts of L. elongata is important to improve ed by fishermen with drift gill nets from understanding of its trophic ecology to contribute to its NanguangtoNanxireachintheYibinreachof management and conservation. theupperYangtzeRiver(Fig.1)inspring(April) The goals of the present study were (1) to describe 2012, n=413;summer(July)2012,n=5; autumn the diet of the L. elongata on the Yangtze River, (2) to (October) 2012, n=5; and winter (January) 2013, characterize ontogenetic dietary changes by stomach n=4. Fish were weighed to the nearest 0.1 g, and content analysis and stable isotope analysis, and (3) to body length (standard length) was measured to the investigate seasonal variations in the diet of the nearest 1.0 mm. The 413 specimens captured in L. elongata by the stable isotope technique. The study spring were used to analyze dietary shift in ontog- forms part of a detailed investigation of feeding ecology eny by stomach content, and 67 of those were of L. elongata, and will provide basic data for studying used for analysis of dietary shift by stable isotope the food web of the upper Yangtze River. The results in spring according to different body length of the may also provide information for management plans of L. elongata, and the grouping of the body length rare and endemic fish species in the National Nature for the stable isotope analysis was consistent with Reserve of the upper reaches of the Yangtze River. the stomach content. Nineteen specimens collected throughout the year with drift gill nets (spring, n= 5; summer, n=5; autumn, n=5; winter, n=4) were Materials and methods used to analyze seasonal variation in diet. Study area Stomach content analysis The area of the Upper Yangtze above Yichang is an Immediately after their collection, individuals were eu- exceptional ecosystem with unique geology, thanized, and stomachs were dissected and placed in Environ Biol Fish (2015) 98:1965–1978 1967 Fig. 1 a location of Yibin reach in the Yangtze River, China, b sampling area in Yibin reach 10 % buffered formalin until processing. In the labora- Stable isotope analysis tory, stomach contents were separated using a dissecting microscope, and the food items were identified to the Muscle tissue was removed from the dorsal-anterior lowest possible taxonomic level using standard taxo- section of the body immediately after capture and stored nomic keys (Ding 1994; Liang et al. 1996; Zhao 2005; at −20 °C until use. Each sample was oven dried at Zhou and Chen 2011). Items of each identified taxon 60 °C for 48 h and ground to a fine homogeneous were counted, and wet mass of each prey item was powder using a mortar. Sixty-seven specimens captured weighted to the nearest 0.1 mg by electronic analytical in April were separated into 11 size classes: 70–89 mm, balance for per stomach. Food items were grouped into n=5; 90–109 mm, n=10; 110–129 mm, n=9; 130– eight categories to reduce error caused by comparisons 149 mm, n=7; 150–169 mm, n=6; 170–189 mm, n= among taxonomic levels (Cortés 1997): fish, shrimp, 8; 190–209 mm, n=6; 210–229 mm, n=5; 230– gammarid, mollusk, benthic invertebrates, aquatic insect 249 mm, n=3; 250–269 mm, n=3; and >270 mm, n= larvae, plankton, and phytodetritus. prey compositions 5. The grouping of size classes for stable isotope anal- were expressed as a percentage weight (W%) and per- ysis was partially consistent with the grouping of size centage numerical composition (N%), and percentage classes for stomach content analysis. Leptobotia frequency of occurrence (F%) of a prey item in elongata is difficult to capture except in spring, so no stomachs with prey was calculated (Hyslop 1980). The analysis of dietary shift was conducted in other seasons. index of relative importance (IRI,Pinkasetal.1971) Potential L. elongata food items were collected in was also calculated as follows: IRI =(W%+N%)F%. April. Plankton was collected using a 30 cm diameter Fish that had regurgitated, had food in the mouth or net (64 μm mesh) at the surface for 10 min. Six samples pharynx, and those with slack, thin-walled empty were filtered through pre-combusted fiberglass filters stomachs were excluded from the analysis.