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 use of herbs as feed additives for fish showed a stimulating effect on growth, feed assimilation and increase its digestibility. The aim of research was to assess the outcome of feeding dietary cinnamon extract on the survival rate, growth performance, feed conversion and production efficiency of common carp (Cyprinus carpio L.), farmed in recirculation system. Thirty-two carps were distributed in two experimental variants, with two replicates of eight fish per group each. The average weight of the carps from the control and experimental group (CG) and EG) was 866.56 ± 113.99 g and 869.38 ± 96.88 g, respectively (p>0.05). The average individual carp grown EG was by 18.98% higher vs CG fish, with no significant differences between groups (p> 0.05). The economic efficiency of feed with extract of cinnamon in the experimental group had better coefficient of economic efficiency 2.71, which is lower by 4.61% compared to the coefficient of the controls

Licorice (Glycyrrhiza glabra) is medicinal plant characterized with sweet flavor which has been used in Bulgarian traditional medicine to improve the condition of the digestive tract and could positively affect digestibility and assimilation of feed nutrients in human and animal organisms. The studies connected with the effect of licorice in fish are limited. The aim of current study was to find the effect of feed supplemented with licorice Glycyrrhiza glabra on growth performance, blood parameters and meet quality in rainbow trout (Oncorhynchus mykiss W.), raised in the recirculation system. The fish were fed with two feeds: control feed (CF) - without the addition of supplement and experimental feed (EF), with supplementation of 300 mg.kg-1 licorice in pellets. The stocking density of rainbow trout in recirculation system was 50 pcs.m-3. The initial average weight of fish in CF variant was 13.30 ±3.07 g and in EF variant was 13.40±3.55 g without differences being statistically significant (p≥0.05). The continuation of the experiment was 60 days. The average final weight, meat quality, and blood biochemical parameters were measured at the end of the experiment. The SGR and FCR were also calculated. Fish from the experimental group fed with a supplement of licorice had with 8.54% higher average final weight compared to the parameter’s value in trouts from the control variant (p<0.05). SGR in rainbow trout’sfrom experimental variants was higher with 6.9% compared to the value of SGR in fish from CF variant. The blood biochemical parameters in experimental trouts were not significantly affected by supplementation of licorice extract. The average values of glucose, ASAT, and ALAT in control variant were higher respectively with 3.96%, 57.2% and 10.3% compared to values in these parameters measured in the blood of fish from the experimental variant, but differences were not statistically proven (p≥0.05). The meat quality parameters were affected from the addition of licorice in feed for trouts and the moisture, fat, and ash quantities were higher respectively with 2.49%, 36.4% and 12.5% compared with the average values of these parameters found for fish from CF group (p<0.05). The extract from licorice added to feed for the feeding of rainbow trout increases the growth of fish and affect the meat quality parameters (p<0.05), but did not affect significantly the blood parameters (p≥0.05).

Aquaponics is innovative recirculation system where hydrobionts are cultivated together with the plants. The possibilities for control of pathogens in these systems are highly restricted. One possible strategy for inhibition of pathogenic microorganisms in aquaponics is the usage of seaweeds extracts. The study connected with the investigation of inhibition effect of seaweeds from Bulgarian Black sea cost on different pathogens is rare. The aim of current study was to test In vitro the inhibition effect of three seaweed species (Ulva rigida, Cladophora vagabunda, and Ceramium rubrum) distributed at Black sea in front of Bulgarian cost on different pathogens (bacteria аnd fungi) which are potentially harmful to hydrobionts, plants and consumer of aquaponics products. The ethanol and methanol extracts from investigated seaweed species were prepared. They were tested with agar well diffusion method against the following fish, food borne and plant pathogens: Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus, Salmonella typhimurium, Candida albicans, Penicillium verrucosum var. verrucosum, Fusarium graminearum, Fusarium moniliforme and Aspergillus ochraceus. The current study showed that the following extracts from seaweeds distributed in front of Bulgarian Black sea cost possess high inhibition effect (size of inhibition zone higher than 10 mm) against potentially pathogenic microorganisms in aquaponics: ethanol extract of C. vagabunda against B. cereus and A. ochraceus, methanol extract of C. vagabunda against C. albicans, ethanol extract of C. rubrum against E.coli, B. cereus and C. albicans.

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Abstract. The aim of the present study was to evaluate the effect of a dietary nutmeg extract supplement on the survival rate, growth performance, feed conversion ratio and economic efficiency of common carp (Cyprinus carpio L.) reared in a recirculation IntroductionDuring the last years, various dietary supplements are used to improve the quality of fish feeds. Their main purpose is to enhance the growth performance of different species, to reduce feed conversion ratio and to increase survival rate. Furthermore, dietary fish feed supplements should improve their utilisation. Numerous feed additives (for example -betaine, L-amino acids and inosine) have been tested (Polat and Beklevik, 1999). Plant extracts are promising not only because they are not expensive, but they are also natural products that are safe for both fish and the environment (Gabor et al., 2010(Gabor et al., , 2011. Although men have used parts of various plants and plant extracts for food, as spices and cures for centuries, their effect on different fish species, their growth performance and health is not yet well studied. It is affirmed that some phytoadditives could be used as an alternative to antibiotics in aquaculture. Predominating research reports investigated the effect of plant additives on the survival of fish and the treatment of various infectious and parasitic diseases (Stratev et al., 2017). Studies that have evaluated the effect of phytoadditives on growth performance and feed conversion parameters in different farmed fish species are, however, few.Nutmeg (Myristica fragrans) is a dioecious evergreen plant growing in the Moluccas and Spice Island of Indonesia, the seeds of which are used as spice. It's known that they have anti-inflammatory, antimicrobial, antibacterial, hepatoprotective and antioxidant properties (Charles, 2012). The anaesthetic effect of Myristica fragrans is reported in common carp (Al-Niaeem et al., 2017), as well as its influence on the growth of African catfish fry (Clarias gariepinus) (Sodamola et al., 2017). The utilisation of nutmeg as a spice and phytomedicine suggests that the plant contains several biologically active substances that could have not only positive, but also negative effect on farmed fish.The aim of the present study was to evaluate the effect of a dietary nutmeg extract supplement on the survival rate, growth performance, feed conversion ratio and economic efficiency of common carp (Cyprinus carpio L.) reared in a recirculation system. Material and methodsObject of study Thirty-two common carps were allotted into two experimental variants, each of them comprising two replications with 8 fish in a group. The average initial live weight of carps from the control group (CG) and experimental group (EG) was 866.56±113.99g and 868.50±111.18g, respectively. Fish were reared in concrete tanks 3 with efficient volume of 0.8m , elements of the recirculation system. They were fed pelleted carp feed with 25% crude protein, produced by the Top mix company, with pellet size of 6mm. The feed of fish...