Notes on Feeding Preferences of Some Cyprinids (Osteichthyes, Cyprinidae) in the Danube Downstream from Belgrade - Page 03

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Regarding diet composition and prey availability (Table 2), it is notable that gammarids are the most common and abundant prey utilized by all analyzed species. An especially high proportion of gammarids in total diet composition was found in vimba bream, whereas Odonata and Diptera were the most rare prey found in low proportion only in vimba bream and white-eye bream, respectively.

Taking into account the availability of particular prey types (Jacobs index; figures 2 to 5), the situation is somewhat different. The gammarids remain the only "universal" prey, but wit lower preference. The highest value remains in Vimba vimba (33%), but this value is way bellow preferences for Odonata (97%) and Trichoptera (91%) . The registered preference of vimba bream for gammarids of vimba bream is in accordance with the literature, as Uiblein (1992) stated that its populations in the Danube prey on gammarids. It is also notable from Figure 2, that V. vimba avoids chironomids and Diptera.

Common bream prefers hironomids (37%) and gammarids (29%), while avoiding Trichoptera, Diptera and Odonata (Figure 3). The observed diet composition of A. brama could indicate interspecific competition (Piria, 2007) and/or intraspecific competition (Persson and Brönmark, 2002).

Trichoptera (98%) and Diptera (94%) are the preferred prey of Ballerus sapa, while molluscs and Odonata are avoided (Figure 4). Diet preferences, similarly to the previous case of A. brama, could be explained by the pronounced interspecific and/or intraspecific competition. Registered food preferences of Abramis species are in accordance with literature data, where it is stated that bream and white bream are specialized for feeding on dipteran larvae in the sediments or organisms associated with the sediments (Lammens and Hoogenboezem, 1991), while due to limited "pharyngeal crushing power" they are not well adapted to molluscs as a food source (Nagelkerke and Sibbing, 1996).

Blicca bjoerkna showed a higher preference for gammarids (26%), followed by molluscs (17%). Examined specimens of this fish species avoided chironomids, Trichoptera, Diptera and Odonata (Figure 5). Avoidance of chironomids, should be noted, as literature states that, besides gammarids and molluscs, chironomids should be the main food source for this species (Bubinas and Ložys, 2000; Simonović, 2006). It should also be mentioned that compared to other analyzed species, B. bjoerkna showed the highest preference for molluscs.

All four analyzed fish species are omnivores (Lammens and Hoogenboezem, 1991; Simonović, 2006), but only a single specimen of A. sapa and B. bjoerkna have been registered with the presence of plant material in their diet. Due to the specific nature of this plant component, these data have not been further processed or included in the final result.

Although zooplankton is the dominant food of younger/smaller cyprinds, up to 15 cm long (Lammens and Hoogenboezem, 1991; Bănărescu and Coad, 1991), and moreover large bream specimens (up to 30 cm) can also feed on zooplankton (Biró et al, 1991), in our investigation this component of diet was not found. The reason for this is that our study didn’t cover younger specimens that consume zooplankton as primary food. Also it is possible that, although, fish had eaten zooplankton, remains of it were not found in our samples, due to the pronounced trituration of the examined material/gut content.

In summary, we showed that in the investigated part of the Danube near Belgrade, the most important and common food component (prey) for the analyzed cyprinids were gammarids. Knowing that in large potamon rivers in Serbia gammarids are common, and moreover one of the dominant aquatic macroinvertebrates (Paunović, 2007; Paunović et al, 2007; Tubić et al, 2013), and having in mind their general importance as fish food (Macneil et al, 1999), this situation is not so unexpected. Similar results, with gammarids as an important food resource for fish in this part of the Danube, were obtained by Đikanović (2011). Molluscs and especially oligochaetes, as the other dominant and most common macroinvertebrates in potamon-type rivers in Serbia, are far less utilized (molluscs) or completely avoided (oligochaetes), as a prey/food. The reason could be more direct availability/accessibility of gammarids (unlike oligochaetes, which are usually buried in sediment) and their easier catching (unlike molluscs, which are attached to or buried in substrate).



The study was supported by the Ministry of Education and Science of the Republic of Serbia – Grants No. TR 37009 and No. III 43002. Authors would like to thank Dr. Predrag Cakić, Dr. Vesna Đikanović and Goran Avalić from Institute for biological research "Siniša Stanković" in Belgrade for valuable help.