Feeding Habits and Predatorprey Size Relationships of Mandarin Fish

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. (2007). The relationships of the GW and the GH to examined using regression analysis. The relationships between TL were determined. A total of 401 mandarin fish were col- the four prey fish TL and BD were also determined by linear lected and examined during the investigation (162 in spring, regressions. To examine ontogenetic variation in the diet, 39 in summer, 76 in autumn, 124 in winter). mandarin fish were divided into three size groups: small Prey fish were also sampled seasonally using three (<217 mm TL), middle (217–307 mm TL) and large trap-nets to assess prey availability and size structure when (>307 mm TL). Percent wet weight (% W) was used to esti- mandarin fish were sampled. Each trap-net set had two mate the dietary importance of each food category. Prey fish cod-ends, with 2 m depth and 6 mm nylon mesh. Twelve were sorted and % W was recorded for the major prey taxa trap-nets were completed during each season. Pop-nets (Hyslop, 1980), then compared between different seasons and (10 m2, 1 mm mesh size) were used to collect prey fish quan- size groups. The differences in the diet composition with titatively. All prey fish were measured for total length (TL) respect to season and size groups were assessed by Chi-square

Table 1 Physico-chemical characteristics (mean ± SE) in Lake Xiaosihai at diﬀerent seasons in 2007

Parameters Spring Summer Autumn Winter Annual mean

Water temperature (°) 25.4 ± 0.1 29.1 ± 0.0 15.6 ± 0.12 6.7 ± 0.1 19.2 ± 2.0 Secchi depth (cm) 58.0 ± 2.5 44.0 ± 2.9 64.2 ± 4.3 88.6 ± 9.3 63.7 ± 4.0 pH 7.54 ± 0.1 8.24 ± 0.1 8.30 ± 0.1 7.41 ± 0.1 7.88 ± 0.1 Conductivity (lScmÀ1) 327 ± 7.8 362 ± 3.2 338 ± 4.9 260 ± 1.4 322 ± 8.8 Dissolved oxygen (mg LÀ1) 7.38 ± 0.2 7.10 ± 0.1 7.46 ± 0.1 11.17 ± 0.3 8.28 ± 0.4 Total nitrogen (mg LÀ1) 1.060 ± 0.15 0.662 ± 0.14 0.448 ± 0.06 0.684 ± 0.03 0.714 ± 0.07 Total phosphorus (mg LÀ1) 0.071 ± 0.01 0.048 ± 0.01 0.048 ± 0.01 0.042 ± 0.01 0.052 ± 0.01 Chlorophyll a (lgLÀ1) 6.65 ± 1.3 13.11 ± 2.6 7.46 ± 0.9 4.73 ± 0.2 7.99 ± 1.0 Feeding habits and predator-prey size relationships 3

Table 2 Table 3 Linear regression for relationships between total length (TL, mm) Diet composition in 2007 of mandarin fish, Lake Xiaosihai, and body depth (BD, mm) of four dominant prey fish for mandarin expressed as frequency of occurrence (% O), number (% N) and wet fish, Lake Xiaosihai weight (% W) in percentage

TL Prey taxon Prey range species (mm) Equation N R2 P Scientiﬁc name Common name %O %N %W

Topmouth 21–96 BD = 0.210TL À 2.722 276 0.99 <0.001 Fish gudgeon, Cypriniformes 63.45 63.51 72.93 P. parva Cyprinidae Sharpbelly, 54–173 BD = 0.142TL À 4.846 190 0.98 <0.001 Pseudorasbora parva Topmouth 31.72 27.33 22.83 H. leucisculus gudgeon Redfin culter, 44–353 BD = 0.202TL À 1.870 142 0.99 <0.001 Hemiculter leucisculus Sharpbelly 11.24 6.5 16.62 C. erythropterus Cultrichthys erythropterus Redfin culter 7.23 5.67 9.07 Crucian carp, 28–380 BD = 0.269TL À 5.600 148 0.99 <0.001 Carassius auratus Crucian carp 6.02 3.67 10.80 C. auratus Abbottina rivularis Rounded 5.22 2.5 2.23 gudgeon Sarcocheilichthys Rainbow 4.82 4.17 4.31 test (v2) of the frequency of a given prey (Sokal and Rohlf, nigripinnis gudgeon 1981; Sley et al., 2009). The Kolmogorov–Smirnov (K–S) test Acheilognathus Bitterling 1.61 0.83 0.55 chankaensis was used to examine differences in the length-frequency distri- Acheilognathus Bitterling 1.61 0.67 1.45 bution between prey in the diet of mandarin fish and the same macropterus prey in the environment (John, 2001). Least square regres- Toxabramis swinhonis – 2.01 1.00 1.93 – sions were fitted to estimate the relationships between prey Squalidus nitens 1.20 0.50 0.32 Paracheilognathus Bitterling 4.42 2.17 0.44 size and predator size. All analyses were performed using the imberbis SPSS 13.0 statistical package (SPSS Inc., Chicago, IL, USA). Rhodeus sp. Bitterling 14.06 8.5 2.38 Perciformes 14.46 8.17 22.82 Gobiidae Results Rhinogobius giurinus Barcheek goby 5.62 2.67 0.49 Eleotridae Total length and mouth gape size Odontobutis obscurus Dark sleeper 5.22 2.17 5.70 Mandarin fish TL ranged from 91 to 539 mm and the mean Micropercops swinhonis Swinhon’s 1.61 0.83 0.10 TL of 255 ± 74.5 mm (mean ± SD). Fish TL significantly sleeper Ophiocephalidae correlated with both gape width and gape height (Fig. 1). Channa argus Chinese 0.80 0.33 0.27 For fish ranging from 90 to 300 mm in length, the gape snakehead height of mandarin fish exceeded gape width, while for fish Mastacembelidae over 310 mm, the gape width exceeded gape height. Mastacembelus sinensis Large spiny eel 2.01 1.00 1.46 Serranidae Siniperca chuatsi Mandarin fish 0.40 1.17 14.80 Siluriformes 1.20 0.50 0.19 Diet composition Bagridae A total of 401 stomach contents were analyzed, of which 249 Pelteobagrus fulvidraco Yellow catfish 1.20 0.50 0.19 contained food. The diet of mandarin fish in Lake Xiaosihai Other prey Macrobrachium 18.47 10.33 2.00 included 24 recognizable prey taxa, with 18 species of fish Caridina 29.32 16.33 0.61 and six invertebrate taxa (Table 3). Fish were the dominant Odonata 0.80 0.33 0.03 prey taxa, representing over 95% of the diet by weight and Snail 0.80 0.33 0.02 occurred in nearly 80% of mandarin fish stomachs (Table 3). Unidentified fish 0.80 0.50 0.03 Plant material 30.12 1.37 Topmouth gudgeon was the most important component of

mandarin fish diets, with a frequency of occurrence of 80 GW = –0.21 + 0.13TL, R2 = 0.94, P < 0.001; 31.72% and accounting for 22.83% of the diet by weight. 70 GH = 2.59 + 0.12TL, R2 = 0.93, P < 0.001; Sharpbelly Hemiculter leucisculus (Basilewsky), redfin culter 60 n = 401 Cultrichthys erythropterus (Basilewsky) and crucian carp Carassius auratus (Linnaeus) were the next important prey 50 taxa, accounting for over 9% of the diet by weight, respec- 40 tively (Table 3). The mandarin fish were also cannibalistic, with other mandarin fish comprising 14.8% of the diet by 30 weight. However, only seven small mandarin fishes were con- Gape size (mm) 20 Gape width sumed by a mandarin fish of 513 mm TL. Shrimp prey, Gape height 10 including Macrobrachium and Caridina, were less important food items by weight, but still occurred in nearly 20 and 30% 0 0 100 200 300 400 500 600 of mandarin fish stomachs, respectively (Table 3). Total length (mm)

Fig. 1. Linear least-square regressions between total length (mm) Seasonal variation and gape width (mm) (●) and between total length (mm) and gape height (mm) (□) for mandarin ﬁsh, Siniperca chuatsi, in Lake Xiaosi- Results of the contingency table analysis indicated there were hai signiﬁcant seasonal variations in the diet composition of 4 W. Li et al.

2 mandarin fish (v = 168.9, d.f. = 21, P < 0.001) (Fig. 2). 56 136 57 Sharpbelly was mostly eaten during spring and summer, 100% accounting for nearly 36% and over 33% of the diet by weight, respectively (Fig. 2). Topmouth gudgeon represented 80% the greatest proportion of prey fish consumed during autumn 60% Others and winter, accounting for nearly 32% and over 26% of the Shirmp diet by weight, respectively. Topmouth gudgeon, crucian Other fishes carp, and dark sleeper Odontobutis obscurus (Temminek et 40% Rhodeinae Schlegel) were the next three important prey fish during C. auratus spring, while redfin culter, sharpbelly, crucian carp, and dark 20% H. leucisculus sleeper together accounted for over 47% and over 34% of Percent of weight (%W) C. erythropterus P. parva the diet by weight during autumn and winter, respectively. In 0% summer, shrimps were the second most important prey. <217 217–307 >307 Size groups (mm) Fig. 3. Diet composition of mandarin fish among size-classes, Lake Ontogenetic variation Xiaosihai, based on percent of weight of major prey groups Ontogenetic variations in the diet of mandarin fish were apparent, with the small size group clearly displaying differences in stomach contents when compared to middle and correlations between the length of topmouth gudgeon as prey large size groups (v2 = 84.2, d.f. = 14, P < 0.001) (Fig. 3). and TL of mandarin or prey BD and predator gape (Figs 4b Larger prey items such as crucian carp, redfin culter became and 5b). There was no significant increase in minimum prey more common, and smaller prey such as topmouth gudgeon, TL for all four prey fish species consumed during ontogeny bitterlings, and shrimps became less common with succes- of mandarin fish. For the four prey fish combined, the sively larger mandarin fish size classes. In the small size mandarin fish TL and prey fish TL, as well as predator gape group, topmouth gudgeon, bitterlings, shrimps accounted for width and prey BD were positively and linearly related 45.4, 17.2, and 9.6% of the diet by weight, respectively, (Figs. 4a and 5a). Similar-sized mandarin fish fed on larger whereas they were of lesser importance in the diet of the two redfin culter than on crucian carp and sharpbelly, and on larger size groups, accounting for 12.7, 1.1, and 1.7% of the larger sharpbelly than on topmouth gudgeon. The body diet in adults, respectively. However, larger size groups (mid- depths of all prey fish consumed were smaller than the gape dle and large size) consumed more crucian carp and redfin width of the mandarin fish, although for crucian carp body culter than the small size group, and the middle size group depths were nearly equal to the gape widths of mandarin fish contained more crucian carp than the large size group. (body depth to predator gape width ratio was 0.99; Fig. 5e).

Predator-prey size relationships Prey selectivity The prey TL to mandarin fish TL ratio (PPR) varied with Mandarin fish exhibited strong selectivity based on prey size prey fish species. The mean PPR were 26, 33, 33 and 23% for topmouth gudgeon, sharpbelly and redfin culter (Fig. 6). for topmouth gudgeon, sharpbelly, redfin culter and crucian The three prey fish consumed by mandarin fish were carp as prey, respectively. The maximum PPR was 0.60 when restricted to a narrower range of sizes than those available in a mandarin fish of 285 mm TL consumed a redfin culter of the environment, respectively. Significant differences were 170 mm. The maximum and mean TL of sharpbelly, redfin detected between the size distributions of topmouth gudgeon culter, and crucian carp consumed increased with increasing (Dmax = 0.623, K–SP< 0.001), sharpbelly (Dmax = 0.360, TL of mandarin fish. The TL of mandarin fish and prey fish, K-S P < 0.001) and redfin culter (Dmax = 0.541, K–S as well as predator gape width and prey BD were positively P < 0.001) captured in the environment and size distributions and linearly related for sharpbelly, redfin culter and crucian of each prey species consumed by mandarin fish. Mandarin carp as prey (Figs 4c–e and 5c–e). There were no significant fish consumed much larger topmouth gudgeon (60–89 mm) than expected based on field size distributions, while smaller sharpbelly (40–99 mm) and redfin culter (60–99 mm) were 88 18 51 92 consumed than expected. 100%

80% Discussion In this study, fish were the dominant food items of mandarin 60% Others fish, which accounted for the greatest proportion of diet by Shirmp weight (over 95%) and occurred in nearly 80% of mandarin Other fishes 40% fish stomachs. The results generally concur with those of past O. obscurus C. auratus studies (Li et al., 1998; Yang et al., 2002). Yang et al. (2002) 20% H. leucisculus reported that fish accounted for 94.5% of the diet by weight Percent of weight (% W) C. erythropterus and occurred in 64.2% of mandarin fish stomachs in Lake P. parva Liangzi. However, our study found that topmouth gudgeon 0% Spring Summer Autumn Winter was the most important prey fish of mandarin fish, whereas Season crucian carp was the most important prey of this fish in Lake Fig. 2. Diet composition of mandarin fish in different seasons, Lake Liangzi (Yang et al., 2002). Previous studies indicated that Xiaosihai, based on percent of weight of major prey groups crucian carp was the most abundant prey fish in Lake Feeding habits and predator-prey size relationships 5

250 (a) Four prey combined 200 Y = 30.0 + 0.168X, n = 258, 150 R2 = 0.14, P < 0.001 100 50 0 250 200 (b) Toumouth gudgeon as prey n = 163, R2 = 0.0001, P = 0.22 150 100 50 0 250 (c) Sharpbelly as prey 200 Y = 23.2 + 0.24X, n = 39, 150 R2 = 0.29, P < 0.001 100 50 0

Prey total length (mm) length total Prey 250 (d) Redfin culter as prey 200 Y = –74.6 + 0.58X, n = 34, 150 R2 = 0.38, P < 0.001 100 50 Fig. 4. Relationships between prey 0 total length and mandarin fish TL for each of four important prey species 250 and for all four prey species com- 200 (e) Crucian carp as prey Y = –56.2 + 0.41X, n = 22, bined, Lake Xiaosihai. Dashed 150 2 lines = theoretical maximum size R = 0.40, P = 0.002 prey that could be ingested by man- 100 darin fish based on fish gape and prey 50 body depth (see Table 2). (b) Y = + = À + 0 14.20 0.601X, (c) Y 32.43 50 100 150 200 250 300 350 400 450 0.890X, (d) Y = 10.54 + 0.625X, (e) Y = À15.89 + 0.469X Mandarin fish total length (mm)

Liangzi (Xie et al., 2001) and topmouth gudgeon in Lake In this study, the diet of large-sized mandarin fish was Xiaosihai (Li et al., 2010). Thus, the difference in dominant obviously different from that of the small-sized fish prey fish consumed by mandarin fish between the two lakes (Fig. 3). The small-sized mandarin fish tended to feed on may result from the difference in prey fish abundance in the small-sized prey, such as topmouth gudgeon, bitterlings and lakes. An effect of prey abundance on prey selection has also shrimps, while the large-sized mandarin fish tended to con- been reported for other piscivorous fish (Kahilainen and sume large-sized prey, such as C. auratus and C. erythropte- Lehtonen, 2003). rus. This indicated an ontogenetic diet shift in mandarin The diet composition of mandarin fish showed significant fish. Similar cases were found by Mittelbach and Persson seasonal variation. These differences are a reflection of the (1998), based on data of 27 piscivorous fish species. changes in the abundance and availability of various prey Moreover, the present study results indicate that mandarin species (Snyder, 1984). The present study revealed that fish are a mouth gape-limited predator (Fig. 4) which pos- sharpbelly was mostly eaten during spring and summer while sess a ‘predation window’ defined by the minimum and topmouth gudgeon represented the greatest proportion maximum size of prey consumed (Claessen et al., 2002). of prey fish consumed during autumn and winter, which The size spectra of a potential prey consumed by mandarin corresponded to expected peaks in their abundance in that fish must be within the predation window set by the preda- season. Other factors, such as life history of prey fish, may tor’s mouth gape size (Fig. 4). also influence prey selection during different seasons. Zhang In our study, the mean prey TL and BD of sharpbelly, (2005) observed that the maximum life-span of topmouth redfin culter, and crucian carp consumed by mandarin fish gudgeon was just over 2 years in Lake Baoan, and that the increased with increasing size of the predator, whereas no spawning individuals died after reproduction. Consequently, such pattern was found for topmouth gudgeon as prey. This the abundance of topmouth gudgeon decreased quickly after was probably due to the fact that topmouth gudgeon is a the spawning season (April–June). This could explain why small-sized species and the maximum size collected in Lake topmouth gudgeon was less important in the diet of manda- Xiaosihai was 96 mm in TL (Table 2), which could be rin fish during spring and summer than during autumn and consumed by most of mandarin fish captured. In another winter. study, Dorner et al. (2007) found that the size of piscivo- 6 W. Li et al.

60 (a) Four prey combined 40 Y = 2.5 + 0.34X, n = 258, R2 = 0.15, P < 0.01 20

60 (b) Topmouth gudgeon as prey 40 n = 163, R2 = 0.004, P = 0.41

60 (c) Sharpbelly as prey 40 Y = 7.4 + 0.29X, n = 39, R2 = 0.30, P < 0.001 20

0 Prey body depth (mm) depth (mm) body Prey 60 (d) Redfin culter as prey 40 Y = –17.0 + 0.91X, n = 34, R2 = 0.43, P < 0.001 20

0 60 (e) Crucian carp as prey 40 Y = –6.5 + 0.79X, n = 22, Fig. 5. Relationships between prey R2 = 0.40, P = 0.0016 body depth and mandarin ﬁsh gape 20 width for each of four important prey species and for all four prey species 0 combined, Lake Xiaosihai. Dashed 0 10203040506070 lines = where prey body depth axis corresponds to mandarin ﬁsh gape Mandarin fish gape width (mm) width axis

rous pikeperch did not correlate significantly with their (Rice et al., 1993). The present study showed that man- prey. darin fish preferred to consume topmouth gudgeon, Prey-size selectivity is usually defined as any difference sharpbelly and redfin culter individuals of 60–79 mm TL, between prey composition in the environment and prey which indicated that this piscivorous fish may cause composition in the diet of the predator (Manly et al., increased mortality of such individuals in the environ- 1972; Chesson, 1983). In the present study, the sizes of ment. Consequently, large-scale stocking of mandarin fish topmouth gudgeon, sharpbelly and redfin culter consumed in the lake may have potential impacts on the size by mandarin fish did not match closely with those sizes structure of these three prey fish. Therefore, further captured in the environment, indicating that mandarin fish research on the prey selection by mandarin fish and its exhibited strong selection on size-specific individuals of the effect on population size-structure of prey species is three prey fish. Moreover, in our study, mean TL of needed for the successful management of fish stocking sharpbelly and redfin culter consumed by mandarin fish fisheries in future. was significantly smaller than that available in the environment, which was similar to the findings of two other studies (Dorner et al., 1999; Dorner, 2002). However, mean TL of topmouth gudgeon consumed by mandarin fish was signifi- Acknowledgements cantly larger than that available in the environment. The dif- The authors would like to thank Dr. Brendan J. Hicks and ference in prey selection could probably be explained by the Dr. Songguang Xie for their constructive comments and fact that sharpbelly and redfin culter showed larger size critical reading of the manuscript. This study was financially spectra in the environment and swim faster than topmouth supported by the Projects of the National Natural Science gudgeon. Foundation of China (Grant No. 30830025 and 30970553), Predation by piscivorous fish is often size-dependent, Special Fund for Agro-scientific Research in the Public leading to increased mortality at specific life stages of Interest (Grant No. 200903048-04), and the R and D Project the prey (Werner and Gilliam, 1984) and to potential of the Ministry of Science and Technology of China (Grant shifts in the size distributions of surviving individuals No. 2012BAD25B05 and 2012BAD25B08). Feeding habits and predator-prey size relationships 7

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