Prey size selectivity of pikeperch (Sander Lucioperca L.) fed with topmouth gudgeon (Pseudorasbora Parva Temminck & Schlegel)

M. Gevezova-Kazakova*, M. Yankova, T. Hubenova, A. Zaikov, G. Rusenov

Institute of Fisheries and Aquaculture, 4003, Plovdiv, Bulgaria
(Manuscript received 29 May 2017; accepted for publication 29 July 2017)

Abstract. The aim of this study is to examine the size selectivity of the pikeperch fed with one of the most widespread weed fish in fish farms, such as topmouth gudgeon (Pseudorasbora parva Temminck & Schlegel). Topmouth gudgeon (Pseudorasbora parva Temminck & Schlegel), separated in two size groups: large – group 1 (body weight of the specimens 8.63 ± 2.68 g, total length 9.58 ± 0.92 cm, and height of the body 2.06 ± 0.33 cm) and small – group 2 (body weight of the specimens 1.10 ± 0.36 g, average total body length of 5 ± 0.62 cm, and height of 0.85 ± 0.13 cm), were used for prey. The experiment was carried out under controlled laboratory conditions, in the course of 40 days, in 7 tanks. One pikeperch and 10 topmouth gudgeons from both size groups, in total 20 preys were placed in each tank. During the experimental period it was observed that pikeperch preferred to feed on smaller individuals, the difference in the number of consumed small and large fish is approximately 2 times (70 to 34, respectively).

Food spectrum of grey mullet (Mugil cephalus L.) along the Bulgarian Black Sea coast

R. Bekova, G. Raikova-Petrova, D. Gerdzhikov, E. Petrova, V. Vachkova, D. Klisarova
Abstract. For the present paper 35 specimens of sea mullet (Mugil cephalus) from different age groups were investigated. The material was collected between May 2010 – September 2011 along the coast, the main points are two: Varna Bay and the mouth of the river Veleka. The main objective of the study was to establish the food spectrum of mullet, and thus a connection could be made between food components. The methods which were used and defined to study the food spectrum and the relationship between different food components are as follows: frequency of occurrence and dominance index of the nutritional components; the filling index and stomach emptiness index, as well as selectivity coefficient of a meal.Results showed that detritus, zoobenthos (Rissoa sp. and Trochammina inflate – 71.43%) and macrophytes (Cladophoraceae family – 63.64%) dominated in stomachs. Several potential toxic species were also found: Amphora coffeaeformis, Pseudo-nitzschia delicatissima, Pseudo-nitzschia seriata, Prorocentrum cordatum, E. pyriformis, P. minimum, Protoperidinium crassipes. The results for the frequency of occurrence (pF) showed that the most common in the stomach of a mullet of the macrophytes are the species of family Ulvaceae – 45.5% ; family Cladophoraceae – 45.5% ; of phytoplankton – Navicula spp (109,09%).; of zoobenthos: Nematoda g.sp. – 42.9% and Trochammina inflate – 28.6 %. The low emptiness index (0.0857) defines the grey mullet as an often eating fish. The small fish reaching up to 3–4 cm eat phytoplankton and zooplankton. Until now, research on the food spectrum of sea mullet by the Bulgarian sector of the Black Sea have not been conducted.