Comparison of ovarian cycles of Hungarian riverine fish species representing different spawning strategies

Investigations on the ovarian cycle of fish species that inhabit Hungarian rivers are necessitated by both environmental and economic reasons. The objective of our research was to explore new fundamental knowledge concerning the ovarian cycle of the white bream (Blicca bjoerkna, Linnaeus, 1758), barbel (Barbus barbus, Linnaeus, 1758), orfe (Leuciscus idus, Linnaeus, 1758) and nase (Chondrostoma nasus, Linnaeus, 1758). Histological investigation of ovaries and determination of proportions of oocytes in different stages of development is an appropriate method for the description of spawning characteristics of these species. Our results show that the GSI value for all four investigated species starts to increase at the end of summer and reaches its maximum before spawning. In the barbel and white bream, the presence of oocytes in the stage of cortical alveoli and the heterogeneous size of oocytes in the stage of vitellogenesis in the pre-spawning period indicate that barbel and white bream are multiple spawners. In contrast, in the orfe and nase, the absence of oocytes in the stage of cortical alveoli and the homogeneous size of cells in the stage of vitellogenesis indicate that orfe and nase are single spawners

Potential of corn distiller’s dried grains with solubles (DDGS) in the diet of European catfish (Silurus glanis)

Two experiments were conducted to evaluate the suitability of corn DDGS as a protein source for European catfish (Silurus glanis). The first experiment consisted of an in vivo digestibility assessment to determine apparent digestibility coefficients for protein, lipid, phosphorus and amino acids available in DDGS. One hundred twenty juveniles (average weight, 154.29 ± 2.73 g) were distributed in recirculation water system equipped with six 1m3 fiberglass tanks (20 fish per tank), which were allotted to two experimental group in triplicates. Juveniles were fed either of the two diets, with or without DDGS (DDGS diet or reference diet) ad libitum till saturation 3 times per day for two weeks. Apparent digestibility coefficient of dry matter, crude protein, crude fat and phosphorus of DDGS ingredient for Europeean catfish were found 49.42 %, 73.39 %, 77.38 % and 87.98 % respectively. The second experiment was conducted for eight weeks to evaluate the effect of corn DDGS on growth, nutrient utilization and metabolism of European catfish. Two hundred forty juveniles of European catfish (average weight, 272.7 ± 37.8 g) were stocked in 1000 L glass fibre tanks in a recirculation system in triplicates. Juveniles were fed with either of the four iso-nitrogenous and iso-caloric (37 % crude protein and 6 % crude fat) experimental diets formulated with the inclusion of 0, 10, 20 and 30 % corn DDGS with partial replacement of soybean and wheat. No significant differences were found between the experimental groups regarding growth performance and plasma biochemical parameters. The liver histopathological observations showed that 20 and 30 % DDGS groups had less vacuolized hepatocytes than the other groups. Both experiments conclude that apparent digestibility of corn DDGS is auspicious for European catfish and 30 % DDGS can be included in the diet of European catfish without compromising the growth performance and nutrient utilization