Inducing reproduction during periods of the year when spawning typically does not occur is an important goal for the feasibility of commercial fish farming. Pre-seasonal propagation of pikeperch generally occurs about 3 months before the natural spawning season. The objective of this study was to assess effects of imposing a thermal schedule for control of water temperature and differing salmon gonadotropin releasing hormone analogue (sGnRHa) dosages on final stages of oocyte growth, and egg quality by optimizing protocol duration and synchronizing spawning time. In Experiment 1, there was analysis of thermal schedule effects for water temperature control when hormonal administrations occurred before or after water warming (WARMING and STABLE, respectively). In Experiment 2, there was assessment of the sGnRHa dosage effects during the warming schedule. In both experiments there was analysis of oocyte diameter from time of sGnRHa administration until the late stages of maturation. There was greater synchrony in time of spawning in specimens of the WARMING group with lesser variability in time from sGnRHa administration to spawning. In Experiment 2, values for reproductive variables were variable among the different groups, without any differences between treatments. Oocyte diameter at the time of sGnRHa administration was correlated with embryo survival. For effective pre-seasonal pikeperch propagation, the selection of breeders based on oocyte diameter, and administration of 5 μg/kg sGnRHa immediately upon transport to hatchery, followed by a 1 °C/d temperature increase to 10 °C, are effective methods for induction of spawning during periods when spawning does not naturally occur.

With the intensification of aquaculture technologies, the amount of feed input and waste material is increasing, creating potentially negative impacts on freshwater habitats receiving effluent from such systems. Changes in biodiversity of zooplankton communities is often used to assess the effects of such impacts. Rotifers are suitable for bioindication of water quality due to their fast reaction to environmental changes. We examined seasonal changes in the diversity of rotifer communities along a 3.5 km section of the biggest oxbow lake in the Tisza River basin, Hungary, that received inflow from an intensive tank-based aquaculture farm. We detected a species-rich rotifer community with 26 species. Using the Rényi one-parameter diversity index families, we found that biodiversity increased away from the point of inflow in spring, but after a summer transition period the situation became partially reversed during autumn. At the beginning of the study period, the nutrient-rich effluent strengthened the dominance of common species, which decreased but did not disappear in summer. In autumn, the extra nutrient input delayed the decline of the rotifer community at the point of effluent.

Semi-intensive common carp (Cyprinus carpio) farm technology uses several feed types affecting the growth performance; however, we know less about their long-term effects on water quality. Herein, we evaluated the effects of three commonly used feeds—moderate levels of fish meal and fish oil feed (FF), plant meal and plant oil feed (PF), and cereal feed (CF) on the nutrient (total nitrogen (TN), total phosphorus (TP) and organic matter (OM)) content of the pond water. The experiment was carried out over three consecutive years from juveniles to market-sized fish. The type of feed affected the net yields, but generally, it did not affect the water quality. The year of sampling, however, was a significant factor affecting TN, TP, and OM, whose concentrations decreased during the three years. Our findings highlight that the age of the stocked fish on water quality has a more pronounced effect than the nutrient profile of the supplementary feed. Additionally, the plant-based feed could provide comparable net yields as the fish meal-based feed without additional nutrient loading in the water column, reinforcing the sustainability of alternative feeds in semi-intensive carp farming.

With the intensification of aquaculture, the structure and dynamics of aquatic ecosystems are highly affected. At the same time, for a pond fish farmer, one of the most important tasks is to establish and maintain stable and favourable zooplankton populations. In this paper, we assess the effects of different supplementary feed types on zooplankton communities in freshwater fishponds. In an outdoor, experimental fishpond system, carp individuals of 2+ years of age were stocked and fed with either a fishmeal-based diet (FF), a plant meal containing experimental feed (PF) or cereals (CT). To compare the diversity of the zooplankton communities, we used the Shannon diversity index, and to assess the effects of environmental factors and the feed ingredients, we applied canonical correspondence analysis. We described the dynamics of zooplankton communities, where the biodiversity of rotifera and Crustacean communities showed temporal differences. In order to examine the effects of feed ingredients, temporal clustering was applied. The different diets did not consistently alter the composition of zooplankton communities. Consequently, the plant meal containing experimental feed had no negative effect on the planktonic biodiversity, which makes it suitable as an alternative feed source for fishponds at the applied level.

The growth of the human population brought about the global intensification of aquacultural production, and aquaculture became the fastest growing animal husbandry sector. Effluent from aquaculture is an anthropogenic environmental burden, containing organic matter, nutrients and suspended solids that affect water quality especially in the water bodies of high biodiversity and conservation value. Water quality assessment often relies on bioindicators, analysing changes in taxonomic diversity of various freshwater organismal groups. Stepping beyond taxon diversity, we used functional and phylogenetic diversities of rotifers to identify factors affecting their community organization in response to an aquaculture effluent gradient in the largest oxbow lake in the Carpathian Basin, Hungary. Sampling was carried out three times per season at five points along a 3.5 km section of the oxbow lake, including the point of effluent inflow. We used eight traits to evaluate functional diversity: body size, trophi type, feeding mode, protection type, body wall type, corona type, habitat preference and tolerance level. Functional and phylogenetic distances among the 24 species identified indicated trait conservatism. Rotiferan diversity increased with increasing distance from the point of influx in spring and summer. Among the factors affecting community organization in spring and summer, we find examples of environmental filtering, while in autumn the role of biotic interaction is more frequent. Under nutrient‐rich conditions in spring and summer, organisms belonging to the same functional group were dominant, whereas under oligotrophic conditions, more diverse but less abundant groups were present. Considering functional and phylogenetic traits allowed us to identify organising forces of rotifer communities in the largest oxbow lake of the Hungarian Lowland.