Search

The recent expansion of the round goby (Neogobius melanostomus) in tributaries of the lower Danube (Bulgaria) prompted assessing potential negative effects on local fish fauna such as competition for food resources. Diet overlap between the round goby and native fishes was analyzed using samples of fishes and macroinvertebrates collected monthly for a one-year period. Significant dietary overlap between N. melanostomus and Barbus petenyi, Perca fluviatilis, Gobio gobio, Vimba vimba, and Neogobius fluviatilis was observed. Dietary overlap in the Iskar River was found to be considerable mainly in the spring months. Conversely, overlap in the Vit River was observed during summer and late fall. The main reason for the overlap noted was the preference for Chironomidae and Hydropsychidae larvae and Gammaridae. The results suggest that there is potential for competition between the round goby and native fish species inhabiting the tributaries of the Danube. Potentially harmful effects on rare, protected fish species in the area are discussed.

Aquaculture production in Bulgaria has increased over the last decade, reaching 16 442 tonnes in 2019. Fish production has doubled in comparison with 2007, while that of mussels has increased tenfold. The Bulgarian contribution to EU aquaculture production has been increasing significantly in both volume and value over the years, making up 1.15% of the volume and 1.0% of the value of EU production in 2019. Freshwater aquaculture accounts for 78% of total production. Common carp dominates with about 29.4% (4836 t), followed by rainbow trout with 29.2% (4820 t) in 2019. The cultivation of sturgeon species and caviar production are among the most dynamically developing aquaculture segments. Mariculture in the Black Sea has increased in recent years, with the production of Mediterranean mussel reaching 2932 tonnes in 2019. An average of 405 farms operated during the period 2010-2019. Four regions (Plovdiv, Stara Zagora, Burgas and Montana) account for 50% of the total fish production. Pond aquaculture is the dominant technology used in Bulgaria, and it serves as the basis for numerous other activities, including management of fish stocks in various water bodies mainly for recreational fishing. Approximately 35 net-cage farms currently operate in bigger dams. Recirculating fish farms output made up only 0.15% of the total amount of aquaculture for the period 2010-2019. The aquaculture sector exhibited difficulties in recovering from the financial crisis of 2007-2008, manifested by a slow growth for the period 2010-2014. From 2015 to 2019 there has been a significant growth, manifested in a sharp increase of total revenue and profitability, especially among the larger enterprises in the sector, as well as an increase in the number of employees, and the labour productivity. As a result, in 2019 the registered total revenue per enterprise and total revenue per employee were more than double the respective figures for 2010. The profits of larger enterprises increased more than three times on average, but smaller entities, micro-enterprises with less than 5 employees, operated at the border line between profit and loss. The COVID-19 crisis could have lasting consequences. Despite EUR 1.2 million direct payments in the sector in 2020, there has been a significant drop in the export of aquaculture products. Consumption of fish and other aquaculture products remains low compared to those in the other EU countries. [ABSTRACT FROM AUTHOR]

The family Gobiidae is the largest teleost family, consisting of more than 2,000 species in more than 200 genera. They have adapted to a wide range of habitats, inhabiting mostly marine and brackish waters. Recently invasive Ponto-Caspian gobies have caused significant changes to the structure of fish assemblage throughout the European waters. The aim of the study was to verify the possibility of identifying three species of the genus Gobiidae based on the analysis of the mitochondrial region of the cytochrome oxidase subunit 1 (COI) gene. 339 samples originated from seven countries and 17 different sites were investigated. Qualitative and quantitative assessment of the extracted DNA was conducted by measuring light absorbance and electrophoretic separation. Approximately 650-bp (base pairs) fragments were amplified from the 5' region of the mitochondrial COI with the PCR (polymerase chain reaction) reaction. Sequences of 652 bp were obtained and compared with reference sequences in the National Center for Biotechnology Information (NCBI). Based on the sequence analysis, we determined that in the analysed geographical regions, the goby preliminary identified morphologically as the round goby was represented by three species: round goby (Neogobius melanostomus), tubenose goby (Proterorhinus marmoratus), and monkey goby (Neogobius fluviatilis). The latter two are newly reported for their new habitats. Genetic characterisation of such populations offers the opportunity to assess their genetic stability, which provides agencies managing the aquatic environment in EU countries with a tool for revising the legislation, including regulations relevant for updating the status of native and invasive species in European waters. [ABSTRACT FROM AUTHOR]

In the present study, we provide data on the first established, self-sustaining population of non-native brook trout (Salvelinus fontinalis Mitchill, 1814), family Salmonidae, in Bulgaria. The brook trout was detected in upland section of the Palakariya River (Iskar basin) at an altitude between 1350 and 1500 m a.s.l. Distribution, abundance and size structure of S. fontinalis were studied in the period 2019-2021. The coexistence of individuals of different sizes (from 4.1 cm to 24.6 cm); no restocking activities in the last 10 years and the suitable environmental habitat features support the contention of a self-reproducing population of S. fontinalis in the Palakariya River. [ABSTRACT FROM AUTHOR]

Length-weight relationships (LWRs), Fulton (K) and relative (Krel) condition factors for Acipenser ruthenus Linnaeus, 1758, Acipenser gueldenstaedtii Brandt & Ratzeburg, 1833 and Acipenser stellatus Pallas, 1771 from the Danube River were estimated. Fish were captured by bottom drifting trammel nets in the period June - August, 2015-2019. A total of 790 specimens were measured and analyzed. More than 80% of the specimens were young of the year (YOY) fish with total length (TL) up to 35 cm. The values of the parameter b of the weight - length relationship for fish with lengths up to 35 cm ranged from 2.433 (A. ruthenus) to 2.859 (A. gueldenstaedtii). For specimens with TL > 35 cm the values of parameter b ranged from 3.227 (A. stellatus) to 3.668 (A. ruthenus). Relative condition factor (Krel) ranged from 1.003 ± 0.020 (A. gueldenstaedtii) to 1.144 ± 0.018 for A. ruthenus. Fulton's condition factor (K) ranged from 0.300 ± 0.003 for A. stellatus to 0.514 ± 0.011 for A. gueldenstaedtii. [ABSTRACT FROM AUTHOR]

In the 1960-1970s, three coregonid fishes (Coregonus albula, Coregonus maraenoides and Coregonus peled) were imported from the former Soviet Union and introduced to some reservoirs in Bulgaria. Irregular import, hatching in local fish-farms and stocking continued until the 1990s. The aim of our study was to examine the occurrence of the alien coregonid species in one of the stocked reservoirs, Iskar Reservoir, and to identify the species recorded based on their morphology. A total of 54 coregonid specimens were collected at five stations in the period from October to March in 2015 and 2016. According to the studied morphometric and meristic data, all the coregonid specimens collected were identified as the Peipsi whitefish, Coregonus maraenoides. The morphology of C. maraenoides from Iskar Reservoir revealed some differences from the native population (Peipus Lake, Estonia and Russia), being most likely a result of adaptation of this species to the local environmental conditions or related to the brood stock management in the fish farms. Our results showed that C. maraenoides has successfully established in the reservoir. The existence of self-sustaining population has been supported by the following: a long period from the last stocking of C. maraenoides to the reservoir up to our study (>15 years); presence of specimens of different size classes in the catches; and presence of sexually mature female and male specimens. [ABSTRACT FROM AUTHOR]