Notes on Feeding Preferences of Some Cyprinids (Osteichthyes, Cyprinidae) in the Danube Downstream from Belgrade - page 01

Material and Methods

Samples were collected in the period from May till November of 2011 on the Danube downstream from Belgrade at four localities - Grocka, Orešac, Smederevo and Kovin; (Figure 1). The samples were taken with trap nets, gillnets, seine and trawl nets of various mesh sizes (32 – 50 mm). Identification of fishes was done by using appropriate keys (Simonović, 2006).The material was frozen and further processed in the laboratory of hydroecology at the Institute for Biological Research "Siniša Stanković", Belgrade.

Standard length (L) and wet weight (W) were measured. After dissection of the ventral cavity, stomach and gut content was analysed and identified under the binocular microscope Carl Zeiss, Stemi 2000-C.

Aquatic macroinvertebrates were not sampled, but data regarding macroinvertebrate communities on this well explored river were obtained through relevant literature (Paunović et al, 2007; Tubić et al, 2013), available databases (BAES; Simić et al, 2006) and internal data.

Fulton's condition factor K (Fulton, 1902) was calculated to estimate overall condition of caught fishes. The formula K=105*W/L³ , W-weight (g), L –standard length (mm), was applied.

To describe selectivity of diet Jacobs' index D (Jacobs, 1974) was used. Many indices have been used to describe selectivity; however, none is generally superior to the rest and none is without bias and increasing error at small proportions (Hayward and Kerley, 2005). There are methods that minimize these biases and Jacobs' index is one of them (Krebs, 1989).

The index is obtained by formula D=r-p/r+p-2rp, where "r" is the percentage of a given type of food/prey used by a given species and "p" is the percentage of this type of food/prey that is available. The resulting value ranges from + 1 to -1, where + 1 indicates maximum preference and -1 maximum avoidance, or in percentage (range from -100% to 100%).

In our analysis 27 fishes, belonging to four cyprinid species were included: vimba bream Vimba vimba (Linnaeus, 1758), common bream Abramis brama (Linnaeus 1758), white-eye bream Ballerus sapa (Pallas 1814) and silver bream Blicca bjoerkna (Linnaeus 1758). The main data regarding sampled fishes/individuals are presented in Table 1. The standard length (L) of the analyzed ten vimba bream fish ranged from 240 to 327 mm, weight varied from 165 to 367 g, and condition factor K ranged from 0.91 to 1.68. The recognizable remains of diet were not found in two individuals. The standard length (L) of the analyzed seven common bream fish ranged from 210 to 300 mm, weight varied from 129 to 415 g, and condition factor K ranged from 1.19 to 1.89. The recognizable remains of diet were not found in one fish. The standard length (L) of analyzed five white-eye bream fish ranged from 225 to 277 mm, weight varied from 145 to 290 g, and condition factor K ranged from 1.14 to 1.58. The recognizable remains of diet were not found in one specimen. The standard length (L) of analyzed five silver bream fish ranged from 206 to 240 mm, weight varied from 141 to 200 g, and condition factor K ranged from 1.45 to 1.97. The recognizable remains of diet were not found in one fish.

 

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Figure 1: Sampling localities on the Danube downstream from Belgrade.

 

Table 1: The Weight, Length, Condition factor and Diet of analyzed cyprinid specimens
Tab01

 

Table 2: Diet composition and prey availability (%)
Tab02