Journal of Applied Ichthyology J. Appl. Ichthyol. (2012), 1–8 Received: May 9, 2011 © 2012 Blackwell Verlag, Berlin Accepted: January 1, 2012 ISSN 0175–8659 doi: 10.1111/j.1439-0426.2012.02044.x Feeding habits and predator-prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in a shallow lake, central China By W. Li1,2, T. Zhang1,S.Ye1, J. Liu1 and Z. Li1 1State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, the Chinese Academy of Sciences, Wuhan, China; 2Graduate University of Chinese Academy of Sciences, Beijing, China Summary individual life history. Thus, information regarding the feed- The diet and predator-prey size relationships of mandarin ing habits of important predators is essential to understand fish Siniperca chuatsi (Basilewsky) in Lake Xiaosihai along the potential effects of fish predation on prey populations the middle reach of the Yangtze River were studied and communities. through stomach content analysis. A total of 401 specimens Siniperca chuatsi (so-called Chinese perch) inhabits waters (91–539 mm total length) were collected in 2007. The diet from the southern Zhujiang River system through to the was dominated by topmouth gudgeon Pseudorasbora parva, north in the Amur River system (Liang et al., 2001). This fish sharpbelly Hemiculter leucisculus, redfin culter Cultrichthys is a piscivorous species throughout its life (Liang et al., erythropterus, and crucian carp Carassius auratus, with signif- 1998). In the past decades, a major conventional fishery prac- icant seasonal and ontogenetic differences. Ontogenetic varia- tice in Yangtze lakes has been to overfish piscivorous fish tion in diet was apparent that larger prey items such as and to stock herbivorous species (e.g. grass carp Ctenophar- crucian carp and redfin culter became more common, while yngodon idellus) and planktivorous species (e.g. bighead carp smaller prey such as topmouth gudgeon, bitterlings and Aristichthys nobilis and silver carp Hypophthalmichthys moli- shrimps gradually declined in the larger fish. Mandarin fish trix), thereby inducing a series of ecological problems (e.g. total length (TL) was strongly related to mouth gape width reduction or elimination of submersed macrophytes, algae (GW) and gape height (GH). Mandarin fish TL and prey fish blooms, and flourishing of small-sized fishes; Chen, 1989; TL as well as mandarin fish GW and prey fish body depth Cao et al., 1991). In recent years, there has been a shift in (BD) were positively and linearly related for sharpbelly, fish stocking from common carps to piscivorous fishes (espe- redfin culter and crucian carp. Strong size selectivity for cially Siniperca chuatsi) to utilize the abundant small-sized topmouth gudgeon, sharpbelly and redfin culter as prey fish resources (Xie et al., 2000; Cui and Li, 2005), and to ease indicated that the piscivorous mandarin fish can have poten- conflicts between fishery development and water quality tial impact on the population size structure of the three prey conservation based on the principle of trophic-cascading fish. effects (Carpenter and Kitchell, 1988; Liere and Gulati, 1992). Previous studies on the diet of mandarin fish in Chinese Introduction lakes reported prey species occurrence in stomachs (Li et al., There is growing recognition of the important role of preda- 1998; Yang et al., 2002). However, the seasonal and onto- tors in regulating ecosystems and sustaining biodiversity genic changes in the diet as well as predator-prey size rela- (Ritchie and Johnson, 2009). Piscivorous fish are the apex tionships were not considered. Other studies have focused on predators and may have direct effects on the density and size the growth and economic benefits of stocking mandarin fish structure, thereby affecting the entire food web (Tonn et al., (Cui and Li, 2005; Zhang, 2007), but did not examine feed- 1992; Claessen et al., 2002; Wysujack and Mehner, 2005; ing habits of stocked mandarin fish and their effects on prey Dorner et al., 2007; Alp et al., 2008). Mittelbach and species. In this study, the diet and predator-prey size Persson (1998), who reviewed the size-dependent predator-prey relationships of mandarin fish were examined in Lake Xiaosihai, relationships for 27 species of piscivorous freshwater fish, a shallow eutrophic lake along the middle reach of the Yan- found that both maximum and mean size of prey increased gtze River. The specific objectives of this study were to deter- with predator size and most of the variation observed in mine seasonal and ontogenetic variations in food the sizes of prey consumed by piscivores was due to differ- composition, the size relationship between predator and prey, ences in piscivore body size. The size ranges of prey vulnera- and the prey selection of mandarin fish. Such results are use- ble to a specific predator size depend on encounter ful to further investigate the effect of large-scaled stocking of constraints at the lower limit, and gape and capture mandarin fish on populations of prey species. constraints at the upper limit (Christensen, 1996; Wahlstrom et al., 2000). The range was referred to as the ‘predation Materials and methods window’ by Claessen et al. (2002), who studied the impact of size-dependent predation on cannibalistic perch population Study site dynamics. They suggested that the lower limit of the preda- Lake Xiaosihai (30°16′N, 114°41′E) is on the south bank of tion window mainly affected population dynamics and the middle reach of the Yangtze River, Hubei Province, the upper limit had an effect on population structure and central China. With an area of 133.3 hm2 and depths ranging 2 W. Li et al. from 1.0 to 1.7 m, the lake is separated from a larger lake and standard length (SL) to the nearest mm, and body (Lake Baoan) by a dyke. In 2007, the lake was mostly weight (BW) to the nearest 0.1 g. To analyze the effect of the covered by Trapa bispinosa and only a small area of the gape limitation of mandarin fish, maximum body depth (BD) littoral zone was sparsely vegetated with Myriophyllum spica- of four important prey fish were also measured (to the tum. The physico-chemical characteristics of the lake during nearest 0.1 mm) using calipers. This was performed at the the four seasons of 2007 are given in Table 1, which shows position of the anterior edge of the dorsal fin (Dorner and that the lake was lightly eutrophic according to the trophic Wagner, 2003). Based on these measurements, the relation- state index (TSI). A total of 42 fish species belonging to 13 ships between TL and BD were determined (Table 2). The families was recorded in the investigation of 2006–2007, of main bones (cleithrum, opercular, preopercular, pharyngeal, which common carp Cyprinus carpio Linnaeus, silver carp, and dentary bones) of potential prey fish were collected and mandarin fish, and Chinese snakehead Channa argus their morphologies were observed. (Cantor) were the most important commercial fishes. For several years prior to this study, the major form of fishery had been the stocking of the Chinese mitten crab Eroichier Stomach content analysis sinensis. In June 2006, 6000 mandarin fish juveniles (mean Stomach contents of mandarin fish were analyzed by count- total length = 63.1 mm) were stocked in the lake. ing and measuring prey organisms under a stereo binocular microscope. Prey fish in stomach contents were identified to species or genus, and other prey identified to genus or order. Fish sampling Lengths of intact prey fish were measured directly. Slightly Mandarin fish were sampled seasonally using gill nets 24 digested prey fish could be identified to species level by exter- April–25 May 2007 (spring), 20 July–25 August 2007 nal morphology and their size was back-calculated by means (summer), 20 October to 22 November 2007 (autumn), and of the linear equations between their standard length and 23 December 2007–20 January 2008 (winter). During each total length. Heavily digested prey fish were identified to spe- season, 30 gill nets with mesh sizes of 30, 40, 50, 60, 70, and cies based on the morphology of intact species-specific bones 80 mm (each mesh type including five gill nets, total net area remaining in predator stomachs, and TL and body weight of of about 1350 m2) were set throughout the lake, then pulled the digested prey fish were back-calculated theoretically up and examined for fish after 4 h in the daytime or 10–12 h according to the regression equations made by Zhang (2005). during the night. Additionally, electrofishing was conducted The importance of different prey taxa in the diet was evalu- at night (20.00 hours to 23.00 hours) in autumn and winter ated using a variety of indices, including percent frequency along littoral zones, with a generator-powered machine (DC, of occurrence index (% O), numerical index (% N), gravi- 4 kW, 220–380 V, 50 Hz). The cathode, a 2 m long copper metric index based on prey wet weight (% W), and the index cable, was at the rear of boat. The hand-held anode (3.5 m of relative importance (% IRI). Among them,% W has been long pole with a net of 40 cm diameter, mesh size 5 mm) the most popular index to describe prey importance and its was used to catch the fish. relationships with fish and prey availability (Persson and Mandarin fish were immediately placed in iceboxes after Hansson, 1999; Pelham et al., 2001). capture and individually measured in total length (TL, to the nearest mm) and weighed (BW, to the nearest 0.1 g). Mouth gape width (GW) and gape height (GH) were measured using Data analysis a caliper rule (to the nearest 0.1 mm) according to Dorner Relationships of mandarin fish GW and GH to TL were et al.