Turkish Journal of Zoology Turk J Zool (2017) 41: 67-81 http://journals.tubitak.gov.tr/zoology/ © TÜBİTAK Research Article doi:10.3906/zoo-1603-34 Seasonal and ontogenetic diet shift of two sympatric cyprinid fish species from the temperate Karamenderes River, Çanakkale, Turkey Şükran YALÇIN ÖZDİLEK* Department of Biology, Faculty of Science and Arts, Çanakkale Onsekiz Mart University, Terzioğlu Campus, Çanakkale, Turkey Received: 15.03.2016 Accepted/Published Online: 28.05.2016 Final Version: 25.01.2017 Abstract: Diet composition and feeding relationships of two cyprinid species, Squalius cii and Barbus oligolepis, from the Karamenderes River, northwestern Turkey, were assessed over a 1-year period. Both species were omnivorous and fed mostly on benthic plant materials (particularly algae) and insects. The diet of B. oligolepis primarily comprised Bacillariophyceae, Diptera larvae, and other insects, while that of S. cii comprised filamentous algae (Cyanobacteria and Chlorophyceae), insect larvae, and adults. Ontogenetic shifts in diet were identified in both species. The ratio of Chlorophyceae in the diet of B. oligolepis showed a gradual increase with increase in its body size; moreover, the number of ingested taxa decreased but diet diversity increased with increasing fish size. There were seasonal variations in feeding intensities of both fish, which decreased in the colder months. Seasonal resource availability was higher for S. cii than B. oligolepis; moreover, diet overlap was significant in the spring and summer. Findings indicate that S. cii may exclude B. oligolepis during limited resource availability conditions. The cooccurrence of these species may be explained by their generalist feeding strategies; ontogenetic and seasonal resource partitioning played an important role in the coexistence of these species. Key words: Freshwater fish ecology, feeding ecology, river ecology, niche, competition 1. Introduction freshwater ichthyofauna is unknown in Turkey as a part of Increases in global environmental problems make the the Eurasian continent. freshwater ichthyofauna one of the major topics in Feeding and diet composition data are used for terms of biodiversity loss, particularly in Mediterranean evaluating biological and ecological characteristics of countries. In Turkey, as well as in other Mediterranean freshwater fish species. Gut content analysis is one of countries, a series of anthropogenic activities such as the earlier methods used in the determination of feeding habitat degradation, pollution, new introduction of patterns such as feeding intensity, trophic level, niche invasive species, and increase in the number of reservoirs breadth, and intra- and interspecific competition of fish and hydroelectric power plants along the streams together species in their habitats (Windell and Bowen, 1978). with climate change threaten the freshwater fish fauna of Biological characteristics such as age and size together this region. These adverse impacts display the importance with environmental conditions such as season play of natural resources considering the range of fish diversity important roles in the diet composition of most fish with high endemism due to representing European, Asian, (Nikolsky, 1963). Ontogenetic diet shifts with seasonal and even African origin (Şekercioğlu et al., 2011; Çiçek changes explain the intra- and interspecific competition et al., 2015) in Turkey, and it requires the development and give valuable data for understanding the condition of effective management plans in this regard. Data on of native populations. The current study focused on the biological and ecological characteristics of inland fish seasonal and ontogenetic diet shift of two sympatric species are crucial to understand and improve effective fish species in a river in a temperate Mediterranean management plans for conservation and sustainable climate (i.e. northwestern Turkey), including Squalius use of freshwater ichthyofauna. However, the big gap in cii (Richardson, 1857) and Barbus oligolepis Battalgil, knowledge of the biology and ecology of native freshwater 1941. These species are the most abundant native fish fish species limits the understanding of the natural species in the Karamenderes River (Sarı et al., 2006; conditions and conservation status of freshwater fish Yalçın Özdilek, 2008; Yalçın Özdilek and Jones, 2014). species and the fate of the biological reserve in terms of Both species are benthopelagic; however, detailed studies * Correspondence: [email protected] 67 YALÇIN ÖZDİLEK / Turk J Zool of the diets and feeding habits of these species have not plates near ancient Troy, reaching into the Çanakkale been published. On a smaller scale, coexisting species may strait (Figure 1). Two reservoirs for irrigation have been exhibit ontogenetic, spatial, or temporal differentiation established in the Bayramiç and Pınarbaşı districts along in resource use in a local community. These fish species the river. The landscape around the Karamenderes River may shift their diet during ontogenesis and/or there may is used for agricultural purposes. The river is ~3–15 m be seasonal changes in resource availability that affect the wide; the habitat is categorized by run, small riffles, and competitive interactions between them (Winemiller, 1989; shallow pools with an abundance of submerged vascular Wood et al., 2016). Therefore, the aim of this study was plants such as Potamogeton sp., particularly during arid to determine the feeding habits by gut content analysis summers. There is no canopy cover and the river bottom and evaluate the feeding relationships between two consists mainly of gravel, sand, and clay. During the study, native temperate-stream fish species across ontogenetic the mean water depth was ~25 cm, and the depth of the and temporal parameters. This study also assessed the river was as high as 80 cm during the rainy winter season trophic level of these species, taking into consideration in some places. Physical and chemical water characteristics the gut length. The relationship between the relative gut are provided in Table 1. length and quality of diet is well known in fish (Wootton, Specimens were collected along a ~2-km section of 1990). A fish with a longer gut length has a predominantly the river below the second reservoir at Pınarbaşı by using herbivorous feeding pattern (Montgomery, 1977; Ribble cast nets (12- and 25-mm pore sizes) once a month. The and Smith, 1982; Kramer and Bryant, 1995). Plasticity in abundances of each species were expressed as catch per gut morphology may be observed in response to changes unit of effort (CPUE), which is a percentage based on the in diet (Sibbing and Nagelkerke, 2000), and relative gut number of specimens per cast net (Thompson, 1992). length may help to ascertain the trophic category of fish Fish were collected by recreational fisheries activities. in order to understand the ecological roles of these species Specimens were placed on ice blocks immediately after and also the feeding relationships between the two species. capture in order to prevent digestion. In the laboratory, the total length (TL) of the specimens was measured to the 2. Materials and methods nearest 1.0 mm and they were weighed (W) to the nearest Fieldwork was conducted from August 2007 to July 2008 1.0 mg; the entire gut tract from the esophagus to the anus along the Karamenderes River (39°53′28″N, 26°17′32″E was removed and measured to the nearest 1.0 mm and then and 39°54′07″N, 26°16′28″E). The Karamenderes River preserved in 4% formaldehyde after labeling. Subsequently, is ~109 km in length and located on the Biga Peninsula, the gut tract was opened and the contents were removed; northwestern Anatolia; it has five main river basins. The the volume and W of the contents (GCW) were measured river originates from the Ağı and Kaz Mountains and is and contents were preserved in 70% ethanol. The food directed to the west and north, after passing the Kumkale organisms in the contents were identified to the lowest Figure 1. The Karamenderes River and sampling station. 68 YALÇIN ÖZDİLEK / Turk J Zool Table 1. Physical and chemical characteristics of water measured in the study area and biological characteristics of specimens. Seasons Parameters Summer 2007 Fall 2007 Winter 2007–2008 Spring 2008 Summer 2008 Temperature (°C) 27.7 17.17 ± 1.2 9.1 ± 3.6 19.6 ± 4.9 24.4 DO (mg/L) 12.1 10.4 ± 0.67 13.2 ± 6.29 9.5 ± 0.1 5.7 pH 8.3 7.6 ± 0.8 8.1 ± 0.72 6.9 ± 0.06 7 Nitrate (ppm) 0.2 0.2 ± 0.19 1.1 0.5 ± 0.05 - Phosphate (ppm) 0.2 0.6 ± 0.41 0.3 0.5 ± 0.12 - Discharge (L/s) - 10.3 ± 0.37 19.1 ± 2.18 11.9 ± 2.21 - Conductivity (µS/cm) 534.7 665.0 ± 145.7 764.0 ± 39.2 429.3 ± 170.8 349 S. cii N (♀ + ♂ + unknown) 6 (3 + 3) 15 (5 + 6 + 4) 1 (0 + 0 + 1) 32 (4 + 22 + 6) 28 (6 + 20 + 2) 16.8 ± 5.3 20.76 ± 8.8 19.44 ± 6.63 18.83 ± 2.42 Total length ± SD (mm) 14.3 (12.3–24.5) (7.8–36.7) (9.0–31.0) (15.1–24.7) 67.0 ± 69.2 177.98 ± 226.96 119.74 ± 112.88 80.70 ± 37.17 Weight ± SD (g) 34.2 (17.3–183) (3.5–730.0) (7.6–428.3) (39.7–216.5) Condition factor 1.27 ± 0.10 1.37 ± 0.23 1.39 1.36 ± 0.19 1.49 ± 0.36 Gut length ± SD (mm) 18.0 ± 3.4 25.6 ± 12.1 15.6 20.9 ± 7.6 17.3 ± 5.11 Relative gut length ± SD 1.34 ± 0.38 1.14 ± 0.37 1.09 ± 0.21 0.92 ± 0.19 B. oligolepis N (♀ + ♂ + unknown) 8 (0 + 3 + 5) 27 (6 + 6 + 15) 25 (9 +16) 16 (1 + 12 + 3) 16.75 ± 2.95 16.11 ± 3.47 18.54 ± 4.33 17.93 ± 4.12 Total length ± SD (mm) (14.2–23.5) (11.1–26.9) (12–28.1) (13.2–26.2) 44.84 ± 23.04 43.49 ± 30.47 76.71 ± 55.61 68.36 ± 48.74 Weight ± SD (g) (25.5–98.8) (12.1–160.1) (15.1–213.4) (22.9–198.3) Condition factor 1.22 ± 0.10 1.19 ± 0.11 1.33 ± 0.13 1.34 ± 0.12 Gut length ± SD (mm) 20.90 ± 4.26 20.19 ± 5.82 27.76 ± 7.68 22.81 ± 7.10 Relative gut length ± SD 1.28 ± 0.32 1.26 ± 0.19 1.49 ± 0.21 1.26 ± 0.21 possible taxon (Pennak, 1953; Prescott, 1964; Foged, 1981; by measuring the uniformity of the distribution via the Demirsoy, 1992) and counted using a Sedgewick rafter Shannon–Wiener diversity index (H) with evenness (E) of counting chamber under a stereomicroscope at 4× and food items as suggested by Levins (1968).