Csaba Hancz

Examination of some factors affecting selection of fish prey by otters ( Lutra lutra ) living by eutrophic fish ponds

In this study the predation and fish prey selection of otters Lutra lutra L. living by eutrophic fish ponds on agricultural land and in a protected area of temperate climate in Hungary were investigated. The correlations between fish in the diet of the otters (by spraint analysis involved 1942 and 1280 samples for the two habitats) and the fish stock available (by harvest and sample fishing) were generally close. Prey selection was significantly related to selected species of a particular size range (p < 0.01). The preference calculations were performed with Ivlevs index of preference (E-i, minimum - 1. maximum +1). Regardless of species, the otters avoided (E-i= -0.51) fish heavier than 1000 g, with a preference for individuals weighing between 500 and 1000 g (E-i = 0.79). No substantial or clear preference was observed in the weight range below 500 g (E-i = - 0.02-0.38). The preference for fish in accordance with their characteristic sites of occurrence within the body of water was also significant (P < 0.0 1). They avoided fish living primarily in open water (E-i= -0.64) and to a lesser degree those occurring near the pond bed (E-i= -0.22). They favoured fish inhabiting the area with a covering of aquatic plants (E-i = 0.46), and showed a preference to a lesser degree for fish living in the shallow littoral regions (E-i = 0. 14). With the cessation of fish farming and the effect of the drastic changes which occurred in the vegetation, the otters fed substantially on the stock of alternative sources of prey such as amphibians and water insects as well as terrestrial animals, and at such times, depending on season, fish became a secondary source of prey.

Preliminary studies on the genetic variability of six Hungarian common carp strains using microsatellite DNA markers

Genetic variation in six Hungarian common carp (Cyprinus carpio L.) strains was evaluated using 12 microsatellite loci. The domesticated (‘Tatai’, ‘Biharugrai’ and ‘Szarvasi’) strains were derived from fish farms. Two of wild strains (‘Tiszai’ and ‘Dunai’) were sampled from brood stocks maintained at fish farms for breeding, and ‘Kis-Balatoni’ wild carp were sampled from the Small Balaton Lake. Pairwise Fst-values (0.013–0.161) were highly significant (p < 0.0001), demonstrating differentiation among strains. The mean number of alleles ranged between 3.9 and 8.2. Overall mean observed heterozygosity was lower (0.557) than the mean expected heterozygosity (0.700). By strain, the only exception to this trend was the Dunai (Danubian), which showed higher mean observed heterozygosity (0.764) than expected (0.602). For five loci the Dunai strain showed extremely high levels of heterozygosity (1.00). Two wild strains exhibited a number of loci (Tiszai, 4; Dunai, 6) that were not in Hardy–Weinberg equilibrium. A relatively high number of private alleles overall (n=26), as well as differences in allele frequencies supported our ability to assign most individual fish (over 90%) to each strain.

Effects of methyltestosterone, tamoxifen, genistein and Basella alba extract on masculinization of guppy (Poecilia reticulata)

days. The treated groups showed no significant difference (P>0.05) in survival percentage while a significant increase (P<0.05) in percentage of males were observed in all the treatment groups compared to that in control. Control fish showed the lowest percentage (44.49%) of males while 17α-methyltestosterone treatment provided maximum (81.90%) males, followed by tamoxifen (80.09%), genistein (70.59%) and B. alba (63.55%). Intersex fish with male like colouration and gonopodium development, but female gonad structure was observed in all the treated groups. The nonsteroidal compounds evaluated in this study showed potential for affecting sex ratios although their potency was lower compared to 17α-methyltestosterone. Further studies are needed to determine an optimum treatment regime with these agents for induction of 100% sex reversal in guppy.

Efficacy of Basella alba and Tribulus terrestris extracts for production of monosex Nile tilapia, Oreochromis niloticus -

The present study was aimed to evaluate the efficacy of Basella alba and Tribulus terrestris for induction of masculinisation in Nile tilpia. B. alba leaves and T. terrestris seeds were extracted with water, ethanol, methanol, dichloromethane, hexane and successive methanol and mixed sex juveniles of Nile tilapia were subjected to dietary treatment with the extracts at the concentration of 0.5, 1.0 and 1.5 gm/kg feed. Treatment with both the plants showed no adverse effect on general fish health. There was no significant interaction effects (P>0.05) of solvent and concentration, and solvent and plant material for percentage of males. But, significant interaction effect (P<0.05) of concentration and plant material was observed for percentage of males. Also, there was significant interaction effect (P<0.05) of solvent, concentration and plant material for percentage of males. For dietary administration of B. alba leaves, the highest percentage of males (83.2±0.7) was obtained by treatment with ethanol extract at the concentration of 1.0 gm/kg feed. For all the solvents, the highest percentage of males was observed at the concentration of 1.0 gm/kg. But, in treatment with T. terrestris seeds, the highest percentage of males (88.9±1.1) was obtained with ethanol extract at the concentration of 1.5 gm/kg feed, which was also the highest percentage of males for all the treatment categories.

Effect of sex on the fillet quality of Nile tilapia fed varying lipid sources

Abstract Effect of sex and three different oil supplementations on main production traits, and fatty acid composition of the fillet and gonads was investigated in Nile tilapia. Males and females had significantly different final weights owing to the occasional reproduction of fish. Diets had no significant effects on the main production traits. The percentage of ALA in the fillet was significantly higher in the males in all diets. Significant differences were found between the two sexes in the n-3 PUFA, resulting in a higher n-3/ n-6 ratio in the males. MUFA and n-6 PUFA percentages and EPA/DHA ratio in the fillet were affected by the fat sources in the diet. The proportion of the main fatty acids showed significant changes in the gonads. Both sex and the diet had a significant effect on LA, AA, and DHA percentages. In case of EPA the males had significantly higher values than the females. ALA was affected by the different diets, the fillets of the LO group containing the highest percentage Regarding the main FA groups, n-3 PUFA, n-6 PUFA, n-3/n-6 ratio and the DHA/EPA ratio were affected by sex and diets.