The objective of these experimental trials was to determine the effect of a mannan oligosaccharide (MOS) derived from the outer cell wall of Saccharomyces cerevisiae strain 1026 on the growth performance and immune status of rainbow trout. Two experiments were conducted, one with eight net cages and the other with eight raceways. The net cage experiment (42 days) involved 14,400 fish with an initial average weight of 30 g. The raceway experiment (90 days) was conduced with 40,000 fish with an initial average weight of 101 g. Both experiments compared a commercial extruded diet with and without 2,000 ppm MOS supplementation. The calculated daily feed was supplied in six equal rations. Body weight, feed intake, and mortality were recorded and samples were taken for analysis of indicators of immune status. All data were subjected to ANOVA, with a net cage or raceway regarded as an experimental unit. Significantly improved performance and immune status were observed in the net cage trial-improved weight gain of 13.7% (P < 0.01), reduced feed conversion ratio (FCR) (P < 0.05), reduced mortality (P < 0.01), and improved indicators of immune status (P < 0.01) for fish fed the MOS supplement compared with controls. Similar significantly improved performance was observed for the MOS-treated groups in the raceway trial-9.97% improved weight gain (P < 0.01), lower FCR (P < 0.01), and reduced mortality compared with the control treatment. In the raceway trials, however, only the indicators of immune status lysozyme concentration, APCA, and CPCA were significantly improved by MOS treatment (P < 0.05). These experimental trials demonstrated the ability of MOS to improve the growth performance, survival, and immune status of rainbow trout produced in net cages or raceways.

Abstract:One of the main challenges in aquaponics is disease control. One possible solution for this is biological control with organisms exerting inhibitory effects on fish and plant pathogens. The aim of this study was to examine the potential of isolating microorganisms that exert an inhibitory effect on both plant and fish pathogens from an established aquaponic system. We obtained 924 isolates on selective King's B agar and 101 isolates on MRS agar from different compartments of a model aquaponic system and tested them for antagonism against the plant pathogen Pythium ultimum and fish pathogen Saprolegnia parasitica. Overall, 42 isolates were able to inhibit both fungi.Although not yet tested in vivo, these findings open new options for the implementation of biological control of diseases in aquaponics, where plants and fish are cultivated in the same water recirculating system.

Problem statement: Only limited information exists on nutrients in salmonoids meat in Bulgaria, which may to be different and vary to a greater extent than the nutrient composition of other fish items. The present paper is aimed to determine the proximate composition, macro and trace elements of Atlantic salmon`s meat. These data could be helpful in judging the value of nutrient composition data as a base for dietary recommendations. Organisms: 12 species of Atlantic salmon (Salmo salar). Approach: The aim of this study was to determine the proximate composition and levels of iron, potassium, sodium, calcium, phosphorus, magnesium, copper, selenium and zinc in Atlantic salmon cultivated for the first time in Bulgaria. The content of protein, fat and ash and concentrations of iron, potassium, sodium, calcium, phosphorus, magnesium, copper, selenium and zinc were determined by automatic systems and electro thermal atomic absorption spectrometry (ETAAS) after microwave digestion. Mean values and their respective coefficients of variation were calculated from the measured concentrations. Conclusion: In order to provide an accurate overview and to be able to calculate reliable dietary intakes, it is important to know the fish composition data.

Aquaponics is combined growing fish and plants in a recalculating system. Therefore, it is very important to achieve optimal conditions for their cultivation. The purpose of this study was to trace the influence of the water used by the cultivated fish on the biomass of the lettuce in the aquaponic system. In this connection, two types of hydroponic sections were built and integrated into an existing recirculation aquaculture system. The hydrochemical parameters were measured during the trial. The duration of experiment was 60 days. Forty specimens from the fish species rainbow trout (Oncorhynchus mykiss) with an average weight of 13.4 g in good health condition were growing of the each of tanks of the aquaponic system. Sixteen lettuce seedlings were planted on the hydroponic section filled with light weight expanded clay aggregate (LECA) and the other sixteen plants were planted on the floating raft hydroponic section. At the end of the trial the fresh weight of the lettuce plants was measured. The productivity of lettuce plants is highly dependent on the type of plant growing medium and the fish biomass. A better removal capacity in ammonium, nitrate and ortho-phosphate were observed in the LECA section compared with the cleaning capacity in the raft section as a part of experimental aquaponics system.

The present research aimed to examine the effect of dietary phytoextracts supplementation on the chemical composition and fatty acid profile in the meat of rainbow trout (Oncorhynchus mykiss W.), cultivated in a recirculation system. The fish were divided into 6 groups: one control (C) and five experimental groups in the food of which phytoextracts of curcumin (EC), paprika (EP), thyme (ET), oregano (EO) and garlic (EG) were added. The inclusion of phytoextracts had no significant effect on growth parameters of fish from EC, EP, ET, EO and EG groups (P>0.05). No statistical differences on water content, protein and lipids were observed in the meat of fish from the control and the experimental groups (P>0.05). Statistically significantly higher value of the dry matter was established in ET group in comparson with C, EC, EP, EO and EG groups (P≤0.001). The values of ash were significantly lower in fish from all experimental groups compared to the control group. The inclusion of phytoextracts did not affect the fatty acid profile of fish from EP, EO and EG groups (P>0.05). Exceptions are EC and ET groups, which had the lowest value of C18:3n-3 α-linolenic compared to those from the control group (P≤0.05, P≤0.001).