Hydrobiologia (2013) 703:247–256 DOI 10.1007/s10750-012-1370-z PRIMARY RESEARCH PAPER Role of body size and temporal hydrology in the dietary shifts of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) in a large floodplain lake Huan Zhang • Gongguo Wu • Huan Zhang • Ping Xie • Jun Xu • Qiong Zhou Received: 9 September 2011 / Revised: 11 October 2012 / Accepted: 22 October 2012 / Published online: 7 November 2012 Ó Springer Science+Business Media Dordrecht 2012 Abstract Seasonal water-level changes in floodplain d13C values were observed among larger anchovies lakes can induce variations in primary and secondary between seasons, indicating a temporal dietary shift. production, thus affecting trophic interactions. In this Anchovies fed primarily on shrimp and fish during the study, we tested the latter by studying size- and temporal low-water season despite the predominance of zoo- hydrology-related shifts in the diet of shortjaw tapertail plankton during the two seasons studied, which indi- anchovy Coilia brachygnathus (Actinopterygii, Engra- cated increased piscivorous reliance. C. brachygnathus ulidae) from Lake Poyang. During the wet season, d13C exhibited higher d15N values during the wet season values ranged from -28.2% for small anchovies to because the food items were 15N-enriched. Human -24.6% for larger individuals, but d15N ranged from waste brought by floods could be another possible 18.9% for smaller fish to 12.4% for larger fish. interpretation. Considering C. brachygnathus is an Significant 13C-enrichment and 15N-depletion occurred important link between plankton production and higher with increasing size, revealing that different carbon piscivorous trophic levels, changes in the species are sources were used as the fish grew. Given the high expected to affect the functioning of lake food webs hydrologic fluctuation levels, significant differences in along the trophic pathway. Keywords Coilia brachygnathus Á Dietary shifts Á Electronic supplementary material The online version of Lake Poyang Á Stable isotope analysis Á Trophic this article (doi:10.1007/s10750-012-1370-z) contains interaction supplementary material, which is available to authorized users. Handling editor: I. A. Nagelkerken Introduction H. Zhang Á P. Xie Á Q. Zhou College of Fisheries, Huazhong Agricultural University, Dietary shifts are a common feature of the early life of Wuhan 430070, People’s Republic of China many fish (MacNeil et al., 2005; Eloranta et al., 2010). H. Zhang Á G. Wu Á H. Zhang Á P. Xie (&) Á J. Xu (&) These phenomena are usually caused by migration, Donghu Experimental Station of Lake Ecosystems, States size-related morphologic constraints, habitat use, and Key of Freshwater Ecology and Biotechnology, Institute other reasons (Grey, 2001; Barbini et al., 2010; Ginter of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, People’s Republic of China et al. 2011) Thus, these behaviors affect species e-mail: [email protected] interaction and community structure (Werner & J. Xu Gilliam, 1984). Dietary shifts can also be expressed e-mail: [email protected] as changes in the trophic levels of fish (Xu et al., 2007; 123 248 Hydrobiologia (2013) 703:247–256 Wang et al., 2011a) that integrate changes in popula- Lake Poyang. Variations in the d13C and d15N values tion dynamics, prey availability, and predator–prey of the particulate organic matter (POM) and primary interactions (Vo¨gler et al., 2009). consumers were determined during the dry and wet Anchovies are a geographically widespread pelagic seasons. We also compared the variations between fish species in marine and freshwater ecosystems. seasons in the carbon and nitrogen isotope signatures They are of great economic and ecological importance among large anchovies and their dominant food items because of their significant biomass. As essential to examine whether a temporal dietary shift occurred. intermediate-level components in aquatic food webs, Using the stable isotope analysis in R (SIAR), a anchovies play an important ecological link between recently published Bayesian mixing model (Parnell plankton and higher piscivorous trophic levels. Most et al., 2010), we estimated the feasible contributions of marine anchovy species that undergo dietary shifts in dominant food sources assimilated by C. brachygna- their early life stage, such as the European (Engraulis thus and further addressed the possible dietary shift encrasicolus) and Japanese (E. japonicus) anchovies mechanisms associated with seasonal hydrologic (Bacha & Amara, 2009; Islam & Tanaka, 2009; Yasue changes. et al., 2010), have been widely studied. However, few studies are available on freshwater anchovy species (Tang, 1987; Xu et al., 2005, 2007). Materials and methods According to the Food and Agriculture Organiza- tion (FAO) Fisheries Synopsis, C. brachygnathus is Study area the only anchovy species that exclusively lives in freshwater environments (Whitehead et al., 1988). It is Lake Poyang (N 28°220–29°450, E 115°470–116°450), one of the dominant fish species in important fisheries located in the northern part of Jiangxi Province, is the in Lake Poyang, a large freshwater floodplain lake largest freshwater lake in China, covering an area of connected to the Yangtze River. Spawning once a year 3,283 km2. The lake receives runoff water from five from April to July, anchovies reach maturity within tributaries, namely Ganjiang, Fuhe, Xiushui, Raohe, 5–6 months (Liu, 2008). Anchovy stocks have been and Xinjiang. Lake Poyang is pivotal to the biodiver- greatly reduced because of the deterioration of lake sity conservation of Yangtze floodplain ecosystems, environments and overfishing (Zhang & Li, 2007). being one of the two largest freshwater lakes that are Thus far, most studies on C. brachygnathus have still naturally connected to the Yangtze River. The concentrated on its taxonomy and nomenclature. lake serves as an important nursery and feeding However, information regarding the feeding strategies ground for numerous fish species, including some of the species, particularly in the Yangtze-connected endangered anadromous species, such as Acipenser lake, is rare. Therefore, research on the dietary shifts sinensis, C. nasus, and Tenualosa reevesii. However, of C. brachygnathus is important to improve current fish biodiversity is seriously threatened by increasing understanding of its trophic ecology, thereby facili- anthropogenic activity in Lake Poyang (Zhang & Li, tating its management and conservation. 2007). The lake undergoes considerable seasonal Seasonal water-level changes in floodplain lakes hydrologic changes, with the high-water period occur- could induce variations in the primary and secondary ring from June to September and the low-water period production, thus affecting trophic interactions. Tro- from October to March. In one hydrologic cycle, the phic patterns of C. brachygnathus may also be affected area of the lake fluctuates from less than 1,000 km2 by seasonal hydrological changes. A previous study on during the dry season to more than 4,000 km2 during the diet of C. brachygnathus was based on stomach the flood period (Yin & Zhang, 1987; Min, 1995). The content analysis (Institute of Hydrobiology of Hubei lake is comparable to a river during the dry season but Province, 1976). However, this technique is often becomes a lake during the flood season. Our study was biased because the diet is only assessed over small conducted in Hukou (Fig. 1), the only outlet connect- temporal scales, and they exclude information regard- ing Lake Poyang to the Yangtze River. This site has ing assimilation (Hyslop, 1980). In the current study, the greatest seasonal water-level fluctuation, averag- the stable isotope technique was used to distinguish ing more than 10 m (Yin & Zhang, 1987; Min, 1995). size-related changes in the diet of C. brachygnathus in Aquatic macrophytes are rare in this region because of 123 Hydrobiologia (2013) 703:247–256 249 Fig. 1 A Location of Lake Poyang in the mid-lower Yangtze River Basin, China. B Lake Poyang area with main towns. The shaded area denotes the approximate location where the samples were collected the rapid water flow and sandy sediment (Guan et al., wet season, 57 individuals were large size, and all in 1987). Anchovies prefer the habitat in the northern the dry season. part of Lake Poyang because of the specific environ- Potential food items of anchovy were also collected mental conditions, consequently becoming the most from the fishing region during the same period. Water important fish resource harvested on an annual season samples were filtered using precombusted glass in Hukou (Liu, 2008). microfiber filters (Whatman GF/F) and then analyzed as POM. Zooplankton (mostly copepods, Mesocy- Sample collection clops) was collected using a plankton net (mesh size, 112 lm) and then transferred into distilled water by Coilia brachygnathus (Actinopterygii, Engraulidae) hand under a microscope to allow gut evacuation. The was collected from a fisherman’s catch in Hukou samples were then filtered through precombusted glass during two hydrologic seasons. Sampling during the microfiber filters (Whatman GF/F). We also collected low-water period was performed on March 5, 2010, the benthic-grazing freshwater snail, Bellamya aeru- and on August 3, 2010 during the high-water period. A ginosa, and the filter-feeding mussel, Corbicula total of 76 and 15 C. brachygnathus individuals were fluminea. Two dominant shrimp species (Macrob- collected during the wet and dry seasons, respectively. rachium