Feeding of Eurasian perch (Perca fluviatilis L.) in three reservoirs in Serbia

Milena Pavlović1, Momir Paunović2 and Vladica Simić1

 

 


1 University of Kragujevac, Faculty of Science, Institute of Biology and Ecology, Radoja Domanovića 12, 34000 Kragujevac, Serbia

2 University of Belgrade, Institute for Biological Research "Siniša Stanković", Despota Stefana 142, 11000 Belgrade, Serbia

 

Abstract

The diet of adult Eurasian perch (Perca fluviatilis) as one of top predators in aquatic ecosystems in Serbia was investigated during 2011, in order to contribute to the knowledge on the food and habitat preference and cannibalism rate of this common and abundant species. Eurasian perch were collected in three reservoirs in Serbia. Fish was found to be the only prey in the analyzed specimens (170). A total of five fish species were found in stomach content, but they were not all represented as a prey in all studied reservoirs. Twelve fish species were present in the nets drawn from the Gazivode reservoir, seven from the Vlasina reservoir, and eight from the Vrutci reservoir. Bleak (Alburnus alburnus) and Eurasian perch were present in the diet of Eurasian perch from all studied reservoirs. Roach (Rutilus rutilus) was prey in all reservoirs, except the Vlasina reservoir. Chub (Squalius cephalus) was found only in the stomachs of the Eurasian perch from the Vrutci reservoir and rudd (Scardinius erythrophthalmus) was found only in the stomachs of Eurasian perch from the Vlasina reservoir. The significant and negative correlation between abundance and biomass was detected only for Eurasian perch from the Vlasina reservoir.

Keywords: predation, Eurasian perch, diet, reservoirs, stomach content

 

 

Introduction

Piscivorous fish are the top predators in many aquatic systems and knowledge of the type, quantity and size of the prey included in their diet is essential to identifying their potential impact in structuring populations at lower trophic levels. Northern pike (Esox lucius L.), pikeperch (Sander lucioperca L.), Eurasian perch (Perca fluviatilis L.) and occasionally eel (Anguilla anguilla L.) are generally considered to be the most important predators in lakes with low water transparency (Dörner et al., 2007). Predation is one of the key factors that structures communities and drives food web dynamics. Natural communities often have multiple predators (Carey and Wahl, 2010).

The Eurasian perch is a freshwater species inhabiting different ecosystems varying from artificial ponds to brackish water (Akin et al., 2011). Eurasian perch can be found throughout Europe, except in the Iberian Peninsula, southern Italy, and the western part of the Balkan Peninsula. Eurasian perch belongs to a group of temperate fishes that spawn in spring when temperature and photoperiod conditions increase after a long period of gametogenesis through autumn, winter, and early spring (Ceccuzzi et al., 2011). In aquatic ecosystems, fishes that change habitat or prey target during ontogeny are often subject to selection pressure and competition at different life stages (Werner, 1988). A shift from littoral to pelagic habitat occurs during the early life history of the Eurasian perch. Larvae of this species migrate from the littoral zone into the pelagic habitat soon after hatching, and stay there for a month or even longer while they feed predominantly on zooplankton. Some juveniles then switch to the demersal mode of life and return back to the littoral zone, or to the benthic zone (Kratochvíl et al., 2008). As Eurasian perch grow, they switch to larger food items, such as benthic macroinvertebrates, and finally turn to piscivory (Allen, 1935; Haakana et al., 2007).

As perch switch feeding behaviour, their social behaviour changes accordingly from shoaling as zooplanktivores (Craig, 2000) towards feeding in small groups (Eklöv, 1992) or solitary (Bruylants et al., 1986) as piscivores. Eurasian perch are vision-oriented selective predators, which depend on good light conditions (Helfman, 1979). Reduced light may have fundamental effects on interactions between fishes and their prey, as many fishes are visual foragers and highly dependent on light to efficiently detect and consume their prey. Decreased light intensity may also affect the competitive interactions between fishes because many fish species are adapted to a particular light climate (Estlander et al., 2010).

Resolving the feeding habits of fish provides an understanding of the trophic interactions among organisms. The feeding habits of fish species also present information on species assemblages and the role of fish in food webs. The trophic position that a species occupies in the community resolves food web interactions (Akin et al., 2011; Simić and Simić, 2012). As fish are an important component of the food web in aquatic systems, their feeding has been investigated for a better understanding of interspecific and intraspecific interactions. The identifications of stomach content allow us to know about food consumption, feeding and assimilation rates, cannibalism and even habitat segregation (Gümüş et al., 2002). A key element in understanding the relationship between aquatic predators and prey is quantifying the rate of energy transfer through consumption. The first step in this process is a detailed analysis of the diet dynamics of the predator species (Liao et al., 2002). The study of the feeding habits of fish based upon analysis of stomach content has become a standard practice (Hyslop, 1980).

The aims of this study were to investigate the diet of adult piscivorous fish specimens of Eurasian perch, and to evaluate whether the abundance and biomass of this predator is in the correlation.

 Materials and Methods

The study included three reservoirs in Serbia: the Vrutci reservoir, the Gazivode reservoir and the Vlasina reservoir (Figure 1).

Morphometric characteristics and trophic status of the studied lakes are given in Table 1.

Sampling was performed from May to the end of September 2011 by using gillnets with mesh sizes (stretched mesh) from 10 to 120 mm, and electrofishing. Electrofishing was conducted in the littoral zone.

 

Fig01

Figure 1: Geographic locations of the investigated reservoirs.

 

Table 1: Morphometric characteristics and trophic status of the studied lakes

Tab01

 

After collection, total length (TL, mm) and weight (W, g) were measured in the field. To prevent further digestion, the gut was removed and preserved in 4% formaldehyde in the shortest possible time interval, immediately after measuring. Material was further processed in "Aquarium Kragujevac", at the Faculty of Science in Kragujevac. There are three basic steps to analyzing the stomach contents of predators: weighing, identifying, and measuring contents (Elliot et al., 1996). In the laboratory, the stomachs were dissected and prey items were sorted, weighed (g), identified to the lowest taxonomic level possible and subsequently counted and maintained in 70% ethanol. Contents were analyzed by counting prey organisms under a binocular and a microscope and identified. In cases where a prey item was largely digested, pharyngeal bones (cyprinids), opercular bones, vertebrae, scales and position of the eyes and mouth were used for identification through the use of keys and field guides.

Percent frequency of occurrence (%F.O), percent by number (%N), and percent by weight (%W) were calculated for each prey type for each of the four species (Hyslop 1980). The main food items were identified using The Index of Relative Importance, IRI. The Index of Relative Importance was calculated combining %F.O, %N and %W:

IRI = (%W+%N) х %F.O (Pinkas et al., 1971).

Percent IRI (%IRI) was used to facilitate interpretation and was calculated by summing IRI values of all prey types and calculating each prey type's percent contribution to the total (Cortés, 1997). Empty stomachs were excluded from the calculation.

The relationship between an abundance and biomass of predatory species was analyzed using the Pearson's Correlation Coefficient (R) calculated using SPSS 16.0 statistical package programs for Windows (SPSS Inc., Chicago, IL, USA).

 

Results and Discussion

The total number of fish species that were present in the nets drawn from the Gazivode reservoir was 12, from the Vrutci reservoir eight, and from the Vlasina reservoir, seven. The dominant species in the Vrutci and Gazivode reservoirs are nase (Chondrostoma nasus), Prussian carp (Carassius gibelio), bream (Abramis brama) and Eurasian perch. In the Vlasina reservoir the dominant species are Eurasian perch, Prussian carp, bleak, chub and bream.

Eurasian perch, Prussian carp and chub are only three species that were present in the nets drawn from all three reservoirs.

The total number of analyzed specimens of Eurasian perch for diet composition was 170. The number of fish with empty stomachs was 33 (19.41%). The total length and weight of the analyzed species are shown in Table 2.

 

Table 2: The total length (cm) and weight (g) of the analyzed specimens of Eurasian perch (mean ± SD)

Tab02

 

Prey items that were found in the analyzed fish included only fish (bleak, roach, Eurasian perch, chub and rudd).

The results of percentages of the Index of Relative Importance (IRI) of prey items are presented in Table 3.

 

Table 3: %IRI values of prey items found in the stomachs of P. fluvitilis

Tab03