Anchovy Engraulis Encrasicolus Research Articles

Climate change, dinoflagellate blooms and sardine in the southern Benguela Current Large Marine Ecosystem

The incidence of harmful algal blooms (HABs) caused by dinoflagellates may be increasing as a consequence of climate change. The southern Benguela Current Large Marine Ecosystem (LME) has experienced extensive dinoflagellate blooms in recent years, one of which occurred during 2011. We analysed in situ and remotely-sensed data collected at that time to characterise the bloom, investigate its possible causes, and assess its impacts on small pelagic fish species. The bloom was dominated by Gonyaulax polygramma, and the spatial extent of the bloom coincided with near-shore aggregations and wash-ups in some localities of sardine Sardinops sagax. Sardine in the bloom area were in poor condition compared to those elsewhere, whereas variation in the condition of anchovy Engraulis encrasicolus and west coast round herring Etrumeus whiteheadi did not appear to be linked to the bloom. High-salinity South Atlantic surface water covered much of the south coast during the bloom and is considered to have suppressed the normal diatom community and promoted the dinoflagellates. We hypothesise that sardine were negatively impacted by the bloom because this species possesses a fine-meshed branchial basket that can retain the dinoflagellates, whereas the other two species have coarse-mesh branchial baskets and cannot retain small particles. We speculate that the retention of these dinoflagellates on sardine gill rakers “irritated” the fish in some way such that they ceased feeding and lost condition. This hypothesis suggests an indirect impact of dinoflagellate blooms on sardine as opposed to a direct effect such as death from toxin ingestion or hypoxia.

The role of sardine as prey for pelagic predators in the western Mediterranean Sea assessed using stable isotopes and fatty acids

This study combined the analysis of fatty acids and stable isotopes of nitrogen and carbon to test the hypothesis that the pelagic food web of the south Catalan Sea has a wasp-waist structure supported by sardines Sardina pilchardus. If this hypothesis were correct, most predators would be expected to have stable isotope ratios and fatty acid profiles consistent with those derived from a sardine-based diet. However, this was true only for mackerel Scomber scomber, blue butterfish Stromateus fiatola, all sea-birds and oceanic loggerhead turtles Caretta caretta. The values of the DHA/EPA index of neritic logger-head turtles and striped dolphins Stenella caeruleoalba were also consistent with a sardine/ squid diet, but their trophic positions were too high. On the other hand, the DHA/EPA index of most predatory fishes in- dicated that anchovies Engraulis encrasicolus and/or horse mackerel Trachurus trachurus were their main prey. Nevertheless, some amounts of low trophic level invertebrates were likely to be consumed by some predatory fishes, because their trophic positions where lower than expected from a fish-based diet only. The heterogeneous distribution of phytoplankton groups above and below the thermocline during the warm season is hypothesized to be the primary reason for this food web structure, although the strong reliance of some seabirds on sardines is the likely consequence of a massive consumption of discards from fishing boats. In short, there is little evidence for a wasp-waist structure based on sardine, which may explain why the populations of predators fluctuate less than the population of sardines.

Influence of trophic pathways on daily growth patterns of western Mediterranean anchovy Engraulis encrasicolus larvae

Influence of trophic pathways on daily growth patterns of western Mediterranean anchovy Engraulis encrasicolus larvae

210Po and 210Pb trophic transfer within the phytoplankton–zooplankton–anchovy/sardine food web: a case study from the Gulf of Lion (NW Mediterranean Sea)

The transfer of 210Po and 210Pb in the food web of small pelagic fishes (from phytoplankton and zooplankton to anchovy Engraulis encrasicolus and sardine Sardina pilchardus) is investigated in the Gulf of Lion (GoL). We present original data of 210Po and 210Pb activity concentrations, C and N stable isotope ratios, measured (i) from different size classes of phytoplankton and zooplankton during spring and winter in different environments of the GoL, and (ii) in two fish species. Significant spatial patterns based on 210Po, 210Pb activity concentrations and 210Po/210Pb ratios in the different plankton size classes are evidenced by hierarchical clustering, both in spring and winter. This variability, also observed for C and N stable isotopes ratios, is connected to local specific pelagic habitats and hydrodynamics. The sampling strategy suggests that 210Po bioaccumulation in the GoL remains at a constant level from the first (dominated by phytoplankton) to the second trophic level (zooplankton), while 210Pb bioaccumulation shows an increase in winter. Based on stable N isotope ratios and 210Po activity concentrations measured in anchovies and sardines, we evidence 210Po bio-magnification along the trophic food web of these two planktivorous pelagic fishes.

Quantifying the projected impact of the South African sardine fishery on the Robben Island penguin colony

Abstract Quantitative methods are needed to evaluate the ecological effects of fishing forage species upon which predators depend. African penguin Spheniscus demersus numbers at the Robben Island colony rose during the 1990s co-incidental with a marked increase in sardine Sardinops sagax and anchovy Engraulis encrasicolus abundances, but decreased appreciably during the 2000s as sardine suffered a series of poor recruitments. A population dynamics model is developed which relates penguin adult annual mortality to local sardine biomass, and is fit to penguin moult counts and re-sightings of tagged penguins. The predator–prey interaction is best explained by a sardine–penguin mortality relationship with average penguin survival decreasing only when the local sardine biomass is less than approximately one-quarter of the maximum observed. Results suggest that the rapid growth of the colony during the 1990s was driven primarily by immigration. Penguin projections are generated by linking to future sardine abundances predicted under the operational management procedure used to set catch limits for these sardine and anchovy fisheries, and compared with equivalent scenarios without fishing. Results indicate that fishing is likely to have a relatively small impact on penguins, especially when compared with uncertainties that arise from the variable spatial distribution of the sardine population.

A joint stock assessment for the anchovy stock of the northern and central Adriatic Sea: comparison of two catch-at-age models

Anchovy (Engraulis encrasicolus, L.) is one of the most important commercial species of the northern and central Adriatic Sea, as well as one of the most productive fisheries in the whole Mediterranean. In the Adriatic Sea the stock of anchovy is shared between Italy, Croatia and Slovenia. A joint stock assessment was carried out using catch data from all the fleets for the time interval 1975-2009. Analyses were performed using estimates of natural mortality at age obtained by means of two different methods and two population dynamics methods based on the analysis of catch-at-age data: Laurec-Sheperd virtual population analysis (VPA) and integrated catch-at-age (ICA), both tuned to acoustic estimates of abundance. Gislason’s estimates for natural mortality appeared to be more realistic and were thus preferred for short-lived species. The general trend of biomass and fishing mortality is similar for the two models, highlighting the major collapse of the stock in 1987. Nevertheless, ICA has enough flexibility to combine all the data available without adding too much complexity in comparison with a VPA approach and seems to perform better in terms of the spawning stock biomass/recruitment relationship and diagnostics (i.e. the retrospective pattern). For the stock status, the exploitation rate from ICA is higher than the suggested threshold of 0.4 proposed by Patterson for small pelagic species.

Some Trace Metals Pollution of Black Sea Anchovy from Crimean Coastal Region (Black Sea and Azov Sea)

Aims: The aim of the present study was to detect the level of three heavy metals cooper, zinc and lead in tissues of commercial fish species anchovy Engraulis encrasicolus in six regions of Crimean coastal waters (Black Sea and Azov Sea), and to compare them with the values obtained in various geographical locations of the world. Study Design: Fish samples were collected from commercial catches at six locations in Black Sea along Crimean coastal area (near the riparian cities Evpatoria, Saky, Sevastopol, Jalta, Alushta, Sudak and Feodosia) and at the region of Arabat Pointer in Azov Sea in springsummer period 2011.

Species identification of small pelagic fish schools by means of hydroacoustics in the Eastern Mediterranean Sea

Reliable biomass estimates by means of hydroacoustics largely depend on the correct identification of acoustic targets. Data collected during five summer acoustic surveys (2004-2008) in the North Aegean Sea (Greece) were analyzed to explore effective discrimination of small pelagic fish schools according to the species they belong. Discriminant Function Analyses (DFA) using bathymetric, energetic and morphometric school descriptors as explanatory variables were applied per research cruise as well as to pooled data from all surveys. Results revealed that the schools can be successfully classified into the five species considered (anchovy Engraulis encrasicolus, sardine Sardina pilchardus, round sardinella Sardinella aurita, blue whiting Micromessistius poutassou, and Atlantic mackerel Scomber scombrus). The percentage of correct classifications in terms of number of schools was higher in the analyses of the annual cruises (75.6%-95.36%) than in the analysis of pooled data (≈72%). This is because of (i) the lower number of species, as well as (ii) the reduced intraspecific variability, occurring in each separate cruise. Significant differences were detected among school descriptors for the different species, revealing discrete aspects of schooling behaviour for each species. The benefit of the specific approach is that the classification functions of the DFAs can be used to classify a larger set of schools, which has not been possible to assign to specific species. Overall the approach constitutes an objective, more automated and less time consuming procedure for the analysis of acoustic data and can contribute to the improvement of biomass estimates in the area.

Feeding of pelagic fish in waters of Mauritania: 1. European anchovy Engraulis encrasicolus, European sardine Sardina pilchardus, round sardinella Sardinella aurita, and flat sardinella S. maderensis

Feeding peculiarities of mass pelagic planktonphagous fish from Canary upwelling water and frontal zones of Mauritania were investigated: European anchovy Engraulis encrasicolus, European sardine Sardina pilchardus, round sardinella Sardinella aurita and flat sardinella S. maderensis. European anchovy and flat sardinella feed mainly on zooplankton crustaceous (89 and 57% of food mass), while round sardinella and European sardine feed mainly on phytoplankton (58 and 55%). Detritus and detritus-algal units compose a significant part in feeding of round sardinella, European sardine and flat sardinella young. This provides the reasons to suppose that detritus in pelagic water of Mauritania serves as an additional diet component next to phyto and zooplanktons. Sea grasses covering an area of 390–490 km2 of shallows in the Gulf of Arguin are the most probable source of detritus.

Is the Target Reference Point (F0.1) vulnerable to changes of natural mortality (M) ? Case of the european anchovy Engraulis encrasicolus (Linnaeus, 1758) from the eastern coast of Algeria.

Is the Target Reference Point (F0.1) vulnerable to changes of natural mortality (M) ? Case of the european anchovy Engraulis encrasicolus (Linnaeus, 1758) from the eastern coast of Algeria.

Dietary change in Cape gannets reflects distributional and demographic shifts in two South African commercial fish stocks

Abstract Seabirds are upper trophic level predators, and are often highly sensitive to changes in the availability of their prey. Altered prey assemblages resulting from fluctuations in oceanographic conditions may be mirrored by shifts in seabird diet. Long-term studies of dietary change in seabirds therefore provide valuable insight into the nature of environmental shifts within the systems in which they forage. In recent decades, the Agulhas region in South Africa has undergone significant oceanographic change related to warming and intensification of the Agulhas current. Concurrent with this change, the population of Cape gannets Morus capensis at Bird Island, Algoa Bay, has grown rapidly, probably as a result of an increased availability of its dominant prey items, sardine Sardinops sagax and anchovy Engraulis encrasicolus. Using one of the longest and most complete time-series available on diet of a seabird (spanning 34 years), we tested for changes in composition and the abundance of dominant prey species of this population. These observed changes were also compared with acoustic survey estimates of their biomass, and annual catch data. Since 1979, the prey composition has remained similar, but the dietary contribution of sardine and anchovy, which fluctuated inversely to each other, increased over the study period. These shifts seem to be reflective of fluctuations in the stock size of sardine and anchovy. Conversely, a third species, saury Scomberesox saurus, dominant in the non-breeding diet of the 1980s, decreased significantly in dietary abundance over the following two decades. It is likely that dietary shifts of Cape gannets at Bird Island were related to climate-mediated oceanographic change. The implications of such changes are discussed.

Small pelagic fish feeding patterns in relation to food resource variability: an isotopic investigation for Sardina pilchardus and Engraulis encrasicolus from the Bay of Biscay (north-east Atlantic)

Small pelagic fish represent an essential link between lower and upper trophic levels in marine pelagic ecosystems and often support important fisheries. In the Bay of Biscay in the north-east Atlantic, no obvious controlling factors have yet been described that explain observed fluctuations in European sardine Sardina pilchardus and European anchovy Engraulis encrasicolus stocks, in contrast to other systems. The aim of this study was therefore to investigate to which extent these fluctuations could be trophodynamically mediated. The trophic ecology of both fish species was characterised over three contrasting periods (spring 2010 and 2011 and autumn 2011) in the area, in relation to potential variation in the abundance and composition of the mesozooplankton resource. Stable isotope analyses of carbon (δ13C) and nitrogen (δ15N) were performed on potential mesozoplanktonic prey items and in the muscle of adult fish, as well as in the liver whenever available, and mixing models were applied. In both springs, the mesozooplankton resource was abundant but qualitatively different. During this period of the year, results based on muscle isotope values in particular showed that S. pilchardus and E. encrasicolus likely do not compete strongly for food. On the medium term, E. encrasicolus always presented a greater trophic plasticity than S. pilchardus, both in terms of feeding areas and in the size of the mesozooplanktonic prey consumed. In autumn, mesozooplankton abundances were lower, and it was likely that S. pilchardus and E. encrasicolus share food resources during this period. No clear links between the variation in the mesozooplanktonic resource and the trophic segregation maintained between adults of both fish species in spring could be made. Although a certain potential exists for trophodynamically mediated fluctuations of both species under specific abiotic conditions (i.e. due to the existing trophic segregation in spring in particular), the overall results suggest that fluctuations in abundance of both fish species are probably not directly linked to their trophic ecology in the Bay of Biscay, at least at the level of adult individuals.

Disentangling the effects of inherent otolith growth and model-simulated ecosystem parameters on the daily growth rate of young anchovies

Otolith increment widths have often been used to infer somatic growth history when studying the influence of temperature and food supply. However, there is no functional relation- ship between otolith accretion rate ('inherent otolith growth') and somatic growth rate; although both may be mediated by temperature and food, the uncoupling of these rates under changing environmental conditions or during ontogenetic transitions can undermine the sensitivity of incre- ment width analyses. We used otolith microstructure analysis to model the daily growth of anchovy Engraulis encrasicolus juveniles collected from the North Aegean Sea in July 2007, December 2007 and February 2009. To assess the environmental causes of seasonal variability in growth we used daily outputs of environmental variables from a coupled 3D hydrodynamic-bio- geochemical model (POM-ERSEM) as a proxy for the potential environment that fish experienced during their development. According to the simulation, juveniles that hatched in late autumn- winter developed in unfavorable conditions (low temperature, low productivity); however, they exhibited wider otolith increments before metamorphosis. To specifically study environmental influences on the daily growth rates, we used the simulated environmental variables in gener- alised additive model (GAM) analysis of otolith increment widths, while also taking into con - sideration inherent otolith growth, expressed by the explanatory variables 'previous increment width' and 'age'. The inclusion of the interaction term 'age' × 'sampling period', rather than 'age', accounted for the seasonal effects on ontogenetic changes (timing and duration of metamorphosis) and the differences in growth-selective mortality among samples. Results showed that the daily growth rate of anchovy is influenced by temperature, exhibiting an optimum at 24.5°C, and increases significantly with increased mesozooplankton concentration (i.e. food availability). The analysis highlights that, in order to infer the daily somatic growth from fish otolith increment data and understand the environmental influences, inherent otolith growth has to be disentangled and otolith width trajectories standardised for between-sample differences in ontogenetic changes and growth selective mortality.

Sympatric Clupeoid Fish Larvae in the Northeastern Mediterranean: Coexistence or Avoidance?

The summer (July 2002 and 2003) larval concentrations of two commercially important clupeoid species (order: Clupeiformes), the European anchovy (Engraulis encrasicolus) and round sardinella (Sardinella aurita), were measured in Kavala Gulf (northern Aegean Sea), in order to examine their distribution patterns. Anchovy was generally most abundant, reaching 13 852 larvae 10 m−2 in 2003 and occurred in more stations compared to round sardinella. Despite the spawning of both species occurring across the entire gulf, the general spatial distribution of their larvae was different, with European anchovy larvae occupying the entire gulf and round sardinella larvae mainly concentrated at offshore stations. The reason proposed for the spatial segregation of their larvae is direct competition for resources. Yet, coexistence of the two species was observed in frontal areas with abundant food resources that prevent competition.

Measurement and analysis of small pelagic fish condition: A suitable method for rapid evaluation in the field

As condition is a key variable in population dynamics (especially for survival, growth and reproduction), the use of well-defined and accurate fish condition indices is capital. In particular, condition indices (morphometric, bioenergetic and biochemical) have never been compared and validated for the European anchovy Engraulis encrasicolus, the European pilchard Sardina pilchardus and the European sprat Sprattus sprattus. The accuracy of two indirect methods, the morphometric relative condition index Kn and the bioenergetics index determined with the Distell Fish Fatmeter was investigated by comparing with a direct measure of relative lipid content carried out with a thin layer chromatography-flame ionization detector. Estimations from the fatmeter correlated quite well with the relative lipid contents of all species, regardless of the reproductive period (R2=0.69 for anchovy, R2=0.75 for sprat and R2=0.48 for sardine). Kn correlated more poorly with relative lipid content (R2=0.22 for anchovy and R2=0.41 for sardine, ns for sprat), especially during the reproductive period, pointing out the difficulty for such an index to precisely reflect changes in fat allocation. During the reproductive period, changes in Kn could reflect other processes, such as changes in protein content. Therefore, these different types of commonly used indices do not reflect exactly the same type of energy stores. The high repeatability of the fatmeter was brought to light, so that only one measurement on each fish side may be necessary to evaluate the relative lipid content of a small pelagic fish. Finally, fatmeter measurements were not affected by freezing storage up to one month for anchovy (R2=0.66) and sardine (R2=0.90), making it possible to use frozen samples of both commercial and scientific survey. In contrast, the freezing storage for sprat should be avoided. Based on this study, the Fatmeter appears to be a suitable indirect method to assess condition and fat content of sardine and anchovy on a large number of individuals.

İzmir Körfezi (Orta Ege Denizi)’ndeki Hamsi Engraulis encrasicolus (Linnaeus, 1758) Yumurta ve Larvalarının Bolluk ve Dağılımı

In this study, the abundance and distribution of anchovy Engraulis encrasicolus (Linnaeus, 1758) eggs and larvae in İzmir Bay were examined in 2013. For this aim, seasonally obtained the plankton samples from 11 stations identified in the bay. Anchovy eggs and larvae were obtained all seasons except winter. As a result, total 6889 eggs/m², 3231 larvae/m² were obtained. The minimum and maximum diameters of anchovy eggs; in short exis 0.49 to 0.56 mm (average 0.51±0.43), in long axist 1.09 to 1.30 mm (average 1.21±0.006). Minimum and maximum larvae length is 2.28-9.8 mm.

Age‐specific survival and movement among major African Penguin Spheniscus demersus colonies

Reliable estimates of survival and dispersal are crucial to understanding population dynamics, but for seabirds, in which some individuals spend years away from land, mortality and emigration are often confounded. Multistate mark–recapture methods reduce bias by incorporating movement into the process of estimating survival. We used a multistate model to provide unbiased age‐specific survival and movement probabilities for the Endangered African Penguin Spheniscus demersus based on 5281 nestlings and 31 049 adults flipper‐banded and resighted in the Western Cape, South Africa, between 1994 and 2012. Adult survival was initially high (≥ 0.74) but declined after 2003–2004 coincident with a reduction in the availability of Sardine Sardinops sagax and Anchovy Engraulis encrasicolus on the west coast of South Africa. Juvenile survival was poorly estimated, but was lower and more variable than adult survival. Fidelity to the locality of origin varied over time, but was high in adults at Robben and Dassen islands (≥ 0.88) and above 0.55 for juvenile and immature Penguins at all localities. Movement occurred predominantly during 1994–2003 and was indicative of immigration to Robben and Dassen islands. Our results confirm that a prolonged period of adult mortality contributed to the observed decline in the African Penguin population and suggest a need for approaches operating over large spatial scales to ensure food security for marine top predators.

Habitat selection response of small pelagic fish in different environments. Two examples from the oligotrophic Mediterranean Sea.

A number of scientific papers in the last few years singled out the influence of environmental conditions on the spatial distribution of fish species, highlighting the need for the fisheries scientific community to investigate, besides biomass estimates, also the habitat selection of commercially important fish species. The Mediterranean Sea, although generally oligotrophic, is characterized by high habitat variability and represents an ideal study area to investigate the adaptive behavior of small pelagics under different environmental conditions. In this study the habitat selection of European anchovy Engraulis encrasicolus and European sardine Sardina pilchardus is analyzed in two areas of the Mediterranean Sea that largely differentiate in terms of environmental regimes: the Strait of Sicily and the North Aegean Sea. A number of environmental parameters were used to investigate factors influencing anchovy and sardine habitat selection. Acoustic surveys data, collected during the summer period 2002–2010, were used for this purpose. The quotient analysis was used to identify the association between high density values and environmental variables; it was applied to the entire dataset in each area in order to identify similarities or differences in the “mean” spatial behavioral pattern for each species. Principal component analysis was applied to selected environmental variables in order to identify those environmental regimes which drive each of the two ecosystems. The analysis revealed the effect of food availability along with bottom depth selection on the spatial distribution of both species. Furthermore PCA results highlighted that observed selectivity for shallower waters is mainly associated to specific environmental processes that locally increase productivity. The common trends in habitat selection of the two species, as observed in the two regions although they present marked differences in hydrodynamics, seem to be driven by the oligotrophic character of the study areas, highlighting the role of areas where the local environmental regimes meet ‘the ocean triad hypothesis’.

Changes in prey availability impact the foraging behaviour and fitness of Cape gannets over a decade

Seabirds respond to environmental changes by adjusting their breeding and forag- ing strategies, but this behavioural flexibility has limits. Cape gannets Morus capensis breeding in the southern Benguela on Malgas Island off South Africa's west coast have experienced large fluc- tuations in natural prey availability over the past decade, linked to environmental change and localised overfishing. When small pelagic fish are unavailable, breeding gannets increase their consumption of low-quality fishery discards (primarily hake Merluccius spp.). To investigate the limits of foraging flexibility of breeding gannets facing variable prey availability, we monitored foraging behaviour, nest attendance, adult body condition and chick growth between 2002 and 2012, along with diet composition and prey abundance (through annual hydroacoustic assess- ments) during the birds' breeding season. The combined biomass of sardine Sardinops sagax and anchovy Engraulis encrasicolus within the Malgas gannet colony's foraging range varied tenfold across the study period and was positively correlated with the proportion of these high quality fish in the gannets' diet (17 to 90%). Foraging effort increased and nest attendance decreased with decreasing sardine/anchovy consumption. Adult body condition was negatively impacted by increases in hake in the diet. Chick growth was lowest when low sardine and anchovy composi- tion was coupled with an increase in adult foraging effort, suggesting a limit to behavioural com- pensation for food shortages. This long-term study demonstrates the consequences of variable prey levels for Cape gannet behaviour and fitness. These results highlight the need for detailed investigations of seabird-fishery interactions, and the necessity to limit fishing within Cape gan- net foraging ranges during years of low natural prey abundance.

Survey of viral haemorrhagic septicaemia virus in wild fishes in the southeastern Black Sea.

Species diversity in the Black Sea ecosystem has been declining rapidly over the last 2 decades. To assess the occurrence and distribution of viral haemorrhagic septicaemia virus (VHSV) in various wild fish species, a wild marine fish survey was carried out in 2009, 2010, and 2011. The pooled or individual samples of kidney, liver, and spleen of 5025 specimens, belonging to 17 fish species, were examined virologically using cell culture. The cells showing cytopathic effects (CPE) were subjected to ELISA and multiplex reverse transcriptase polymerase chain reaction (RT-mPCR), for VHSV and infectious pancreatic necrosis virus (IPNV), after blind passaging to determine the virus species causing CPE. The virus species and possibility of co-infection with IPNV were verified by the RT-mPCR developed in this study. Twelve species of fish (pontic shad Alosa immaculata, red mullet Mullus barbatus, three-bearded rockling Gaidropsarus vulgaris, black scorpionfish Scorpaena porcus, Mediterranean horse mackerel Trachurus mediterraneus, whiting Merlangius merlangus euxinus, stargazer Uranoscopus scaber, pilchard Sardina pilchardus, garfish Belone belone, round goby Neogobius melanostomus, thornback ray Raja clavata, and anchovy Engraulis encrasicolus) tested positive for VHSV Genotype Ie (VHSV-Ie). Except whiting, pilchard, and round goby, the rest are new host records for VHSV. The extent and spread of VHSV-Ie was significantly higher among bottom fish than among pelagic fish. Sensitivity and specificity of the RT-mPCR developed was sufficiently high, suggesting that this assay may be used for both diagnostic and surveillance testing. According to the RT-mPCR results, IPNV was not present in wild fish. These results support the hypothesis that the VHSV-Ie genotype, highly prevalent among fish species in the Black Sea, may have a serious impact on the population dynamics of wild fish stocks.