When paddlefish larvae were reared in tanks and fed on zooplankton, a length of 12-15 cm and a weight of 9.2 g had been obtained by the second month after hatching. After a further 2-months of pond rearing, the survival rate was 48%, and the juveniles had reached an average weight of 27.74 g and length of 22.5 cm. Much better growth rate was achieved when both paddlefish fry and juveniles were reared only on artificial food in tanks. At the end of the first month, a weight of 11.6 g had been reached; at the second month the paddlefish weight was 33.29 g, at the third month it was 60.2 g, and at the fourth month it was 127.7 g. There were two cases in which, respectively, 1,000 and 1,500 paddlefish with an average body weight of 33-60 g were stocked in a reservoir. At the age 5 months the fish had reached, or exceeded, an average weight of 500 g, and, after 1 year, it was over 700 g, which is an indicator of the good rearing opportunities this reservoir offered.

Abstract. The present study investigated the growth performance, weight gain, feed conversion ratio, growth and survival rate of European catfish (Silurus glanis L.) fingerlings reared for one month in tanks with different colours. Four colours were used: light blue, white, green and black. The experimental unit was a flow-through system (0.8 L.min-1) consisting of eight tanks with water volume of 30L, continuous air supply and water heaters. Two hundred fish with an average weight of 1.85±0.62g were stocked in each tank. Results from the study demonstrated that the weight gain and the feed conversion ratio were poorly affected by the tested tank colours. Weight gain is slightly higher in groups A (blue) and B (white) than in groups C (green) and D (black). However, no significant difference was found in terms of weight gain among the experimental groups (p>0.05). Survival rate was the highest in group C (91%) followed by group D (88.5%). Thus, for rearing of European catfish fingerlings it is preferable to use dark coloured tanks, which resemble the natural habitat of the fish.

The purpose of the present study is to investigate the gonadosomatic index (GSI %), the absolute and relative fecundity of one-year-old pike weighing over 400 g and at the same time to study the dependence between the egg size and the size, behavior and vitality of the free embryos obtained from one-and two-yearold spawners. The study involved two weight groups of females, differing in age and body weight and length-one-year-old (W = 514 g, SL = 36.1 cm) and two-year-old matured pike (W = 1454 g, SL = 49.3 cm). Ovary samples were fixed and egg follicles containing maturing oocytes counted and weight. The weight and length of the free embryos from semi-artificial spawning were measured. The results showed that, when raising this species under farmed conditions, more than 40% (in rarer cases 90%) of one-year-old pike females reached over 400 g and 35 cm (SL) and reached puberty. Absolute fecundity of 15,030 follicles (30 follicles per gram body weight) was observed; the GSI was nearly 15% and the follicle weight reached 3.7 mg. This data differs significantly from that obtained from the larger two-year-old fishes: absolute fecundity 41,363 follicles (28 follicles per gram body weight), GSI nearly 20%, follicle weight 5.8 mg. Results showed that the different follicle size determines the free-embryo size. A positive linear correlation was found between the egg follicle weight and the free-embryos weight (r = 0.7143). The free embryos obtain from the one-and two-year-old spawners differed significantly both in terms of their weight (7.13 mg against 10.61 mg) and total length (0.81 cm against 0.97 cm), the differences being 1.5-and 1.2-fold, respectively.

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 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).Keywords: pikeperch (Sander lucioperca L.), prey, topmouth gudgeon (Pseudorasbora parva Temminck & Schlegel), size, selectivity, food AGRICULTURAL SCIENCE AND TECHNOLOGY, VOL. 9, No 3, pp -, 2017 209 212 DOI: 10.15547/ast.2017 IntroductionPredation as a form of relationship between different species is essential for the formation of fish populations. Predators can affect not only species composition, but also the size structure (Bronmark et al., 1995). The presence of predatory fish in water bodies affects significantly the entire ecosystem and can change the feeding behavior or habitat preference of other species (Magnehagen, 2006;Persson et al., 1996).The direct effect of their presence is expressed in reduction in the number of preys, important in this respect being the selectivity of eating, which is defined as total quality for predators (Beyerle and Williams, 1968;Ivlev, 1977; Hart and Hamrin, 1988; Einfalt and Wahl, 1997).The interaction between predator and prey in aquatic ecosystems is highly dependent on their size (Paine, 1976;Olson, 1996). According to Nilsson and Bromark (1999), pike (Esox lucius) prefers to eat smaller prey when there is such choice presented. It is believed that this is determined by the lower risk of failure to catch them. Those who are larger swim vigorously and cause real danger of kleptoparasitism (Nilsson and Bronmark, 1999;2000;Tuersson et al., 2006). The opposite conclusion is reached by Hubenova et al. (2013), who found that pike prefers to feed on larger specimens.The maximum size of prey that predator may eat depends on the morphological constraints of the oral apparatus (Werner, 1974;Nilsson and Bronmark, 2000). In this connection, from entirely anatomical viewpoint the pikeperch has significantly less capacity compared to European pike and Wels catfish.Essential for the choice of prey, except for size, is the shape and height of the body, swimming speed, accessibility, level of satiation of predators, the existence of competition, etc. According to Petrova et al. (1993;1993a) the food spectrum of pikeperch is a reflection of the species composition, abundance, biological and physiological state of the ichthyofauna in the environment. In practice, this choice is determined by a complex set of factors that occur in specific conditions.The issue of selectivity of pikeperch (Sander lucioperca L.) with respect to consumed fish species, including in terms of their ...

Abstract. The purpose of the study is to establish the efficacy of different concentrations of clove oil and the time needed for induction and recovery from anesthesia of European catfish (Silurus glanis L.) fry. The experiment was carried out in laboratory conditions with 50 specimens with body weight 1.11±0.25g and body length 5.45±0.60cm. For the aim of this paper the following five concentrations of clove oil are used: 0.01 ml.l-1, 0.02 ml.l-1, 0.03 ml.l-1, 0.04 ml.l-1 and 0.05 ml.l-1. At the lowest concentration (0.01ml.l-1) the effect is sedative and the fry do not reach the phase of complete immobilization. The application of 0.02 ml.l-1 concentration of clove oil is not beneficial for practical usage, with only 30% of the fish reaching phase 4 of anesthesia. At the highest concentrations (0.04 ml.l-1 and 0.05 ml.l-1) all of the fry were anesthetized for a short time, but the process of recovery was not successful for all of the fry. All of the fry reach phase of anesthesia and recovery without loses at 0.03 ml.l-1. This concentration is advisable for anesthesia of European catfish fry during different manipulations.