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Microbiological method was used to assess peculiarities of abundance of autochthonous and petroleum hydrocarbon-degrading bacteria (HDB) in the digestive tract of fish of different trophic groups and the proportion of HDB in the total heterotrophic bacteria (THB). The number and dynamics of petroleum hydrocarbon-degrading bacteria in the digestive tract of fish was registered in different seasons of the year. Regularities of abundance of petroleum hydrocarbon- degrading bacteria in freshwater and marine fish species were pointed out. The bacteriocenoses of the digestive tract of investigated fish were found to be dominated by the total heterotrophic bacteria. The variability of abundance and dynamics of autochthonous and alochthonous bacterioflora of the digestive tract of fish from the Baltic Sea and the Curonian Lagoon was due to fish species, nutrition habits and intensity, and season of the year. The lowest amount of bacteria of investigated functional groups was observed in early spring, and the highest in summer, during intensive fish feeding. The total heterotrophic bacteria in bacteriocenoses of the digestive tract of river perch and gudgeon from the Curonian Lagoon varied from 10-7 to 10-8 g-1 of intestine content. A similar tendency was observed in fish from the Baltic Sea; however, summer counts of THB in fish from the sea were considerably lower than in fish from the Curonian Lagoon. The greatest part of HDB in THB was observed in summer in the digestive tract of small sandeel (30.95%), European flounder (30.08%) and bullrout (28.33%) from the Baltic Sea. A respective spring proportion was 11.57% in European flounder, 9.88% in sandeel, and 9.24% in bullrout. In autumn this parameter was slightly higher than in spring in the digestive tract of European flounder (18.5%) and the least in bullrout (0.36%). From the proportion of HDB in THB we can assume that the littoral zone of the Baltic Sea near Būtingė is considerably more contaminated with oil than the Curonian Lagoon. The average values of abundance of the total coliform bacteria in the bacteriocenosis of the digestive tract of perch and gudgeon caught in the Curonian Lagoon varied, with the highest values in summer and autumn, whereas in the Baltic Sea the greatest average abundance of total coliforming bacteria (TCFB) was observed in the digestive tract of bulltrout in spring and summer. [ABSTRACT FROM AUTHOR]

Ljunggren, L., Sandström, A., Bergström, U., Mattila, J., Lappalainen, A., Johansson, G., Sundblad, G., Casini, M., Kaljuste, O., and Eriksson, B. K. 2010. Recruitment failure of coastal predatory fish in the Baltic Sea coincident with an offshore ecosystem regime shift. – ICES Journal of Marine Science, 67: 1587–1595.The dominant coastal predatory fish in the southwestern Baltic Sea, perch and pike, have decreased markedly in abundance during the past decade. An investigation into their recruitment at 135 coastal sites showed that both species suffered from recruitment failures, mainly in open coastal areas. A detailed study of 15 sites showed that areas with recruitment problems were also notable for mortality of early-stage larvae at the onset of exogenous food-intake. At those sites, zooplankton abundance predicted 83 and 34% of the variation in young of the year perch and pike, respectively, suggesting that the declines were caused by recruitment failure attributable to zooplankton food limitation. Incidences of recruitment failure match in time an offshore trophic cascade that generated massive increases in planktivorous sprat and decreases in zooplankton biomass in the early 1990s. Therefore, sprat biomass explained 53% of the variation in perch recruitment from 1994 to 2007 at an open coastal site, where three-spined stickleback also increased exponentially after 2002. The results indicate that the dramatic change in the offshore ecosystem may have propagated to the coast causing declines of the dominating coastal predators perch and pike followed by an increase in the abundance of small-bodied fish. [ABSTRACT FROM PUBLISHER]

The Ponto-Caspian round goby ( Neogobius melanostomus, Pallas 1814) most probably was established in the Gulf of Gdańsk, Baltic Sea, in the late 1980’s and has since become one of the dominant species in the region. In this study we assess the role of round gobies as prey for two important fish species in the Gulf of Gdańsk, cod ( Gadus morhua) and perch ( Perca fluviatilis). We compared their present diet with stomach analyses from the area prior the round goby establishment, as well as with diet analysis from Baltic regions where round gobies are absent. There were large differences in the diet between cods from the Gulf of Gdańsk 2003–2006 compared to cods in earlier studies (1977–1981) from the Southern Baltic Sea. There were also large differences in cod and perch diets from areas with and without round goby. Presently, round goby constitutes the most important prey for medium sized cods in Gulf of Gdańsk, and perch from the same area almost exclusively feed on gobiids. Stomach analysis, trophic level estimates, and stable isotope analyses all indicated that cod and perch in Gulf of Gdańsk after the round goby establishment belonged to a similar trophic level. Beside round goby, no mussel feeding fish contributed much to the diet of cod or at all to the diet of perch. Thus, it is likely that round gobies constitute a new energetic pathway from mussels to top predators. However, due to the short time elapsed after round goby establishment, we can only speculate on the species future impacts on Baltic food webs. [ABSTRACT FROM AUTHOR]

Abstract: Organotin compounds (OTCs) leaching from the antifouling paints used in boats and ships have contaminated many water areas worldwide. The purpose of this study was to obtain a general view of the organotin contamination in fish in Finnish lake areas and Finnish coast of the Baltic Sea using perch as the main indicator species. Perch sampling covered areas presumed as less contaminated and areas suspected as more contaminated. Besides perch, 12 other species were sampled from sites presumed as less contaminated. OTCs measured were mono-, di- and tributyltin, mono-, di-, and triphenyltin and dioctyltin. The sum concentration of OTCs (ΣOTCs) in perch in the least contaminated areas of the Baltic Sea were around 20ng/g fresh weight (fw) and less than 10ng/g fw in lake areas. In heavily contaminated areas of the Baltic Sea 150–500ng/g fw in perch were detected. In lake areas the maximum ΣOTCs in perch was only 30ng/g fw. With regard to the other species in the Baltic Sea, salmon, sprat, flounder, whitefish, vendace and lamprey contained low concentrations (ΣOTCs mainly less than 20ng/g fw), whereas in pike, pike-perch, burbot and bream concentrations were higher. ΣOTCs in lake fish were generally lower than in the Baltic Sea. In a distance gradient study, ΣOTCs in perch decreased quickly from nearly 200ng/g fw at a contaminated harbor area to 35ng/g fw during a distance of 5km. Further decrease was slower and reached 15ng/g fw at 100km. In a size dependence study triphenyltin showed better correlation with the fish length than tributyltin for all species studied, i.e. for perch (0.16 vs 0.26), pike-perch (0.13 vs 0.24) and roach (0.46 vs 0.80). High correlation for roach may be partly explained by smaller number of samples collected and small length range. [Copyright &y& Elsevier]

The effects of temperature, water level and moon phase on the movements of pikeperch ( Sander lucioperca) were studied during pre-spawning and spawning season from April to June. Trends in catches and temperature were removed with linear regression. Cross-correlation analysis showed that temperature change one and two days earlier had the strongest effect on catches. Close to the new moon, pikeperch catches increased, whereas changes in water level had no effects on movements. [ABSTRACT FROM AUTHOR]

Nursery areas of perch, Perca fluviatilis L., in the shallow coastal areas of the Baltic Sea are affected by increased water turbidity due to the ongoing eutrophication and other physical disturbances. Visually feeding fish, such as perch, which depend on clear water and good light conditions for effective foraging are often negatively affected by turbidity. We tested the following hypothesis: in laboratory experiments increased turbidity combined with decreased light intensity impairs the foraging efficiency of juvenile perch. Consumption of the mysid shrimp, Neomysis integer Leach, by 0+ perch (4–5.2 cm) and 1+ perch (6.1-7.7 cm) was tested at four levels of turbidity (1, 10, 20 and 30 NTU = Nephelometric Turbidity Units) combined with three light intensities imitating daylight (64–71 μmol m-2 s-1), twilight (1.0–1.2 μmol m-2 s-1) and night (complete darkness). There were no significant reductions in the consumption of mysids by 0+ and 1+ perch with increased turbidity and decreased light intensity in 3 h trials. The consumption of mysids by 0+ perch decreased slightly, although not significantly, with increasing turbidity in 1.5 h trial. This indicates that there are compensatory factors (e.g. increased activity of perch, increased prey encounter, reduced anti-predator behaviour of prey, altered contrast of prey) acting on reduced visual ability of juvenile perch due to increased turbidity and low illumination. [ABSTRACT FROM AUTHOR]

Pikeperch and perch perform seasonal migrations between the Curonian Lagoon and the coastal waters of the Baltic Sea. The Curonian Lagoon is a freshwater basin, while salinity in the coastal waters varies between of 4.9–6.8 psu. In the Curonian Lagoon water temperature is generally higher than in the coastal waters. Field studies of growth and condition characteristics of pikeperch and perch were carried out in these water bodies with the aim to estimate growth differences of the two fish species under different salinity and temperature conditions. Additionally, an experimental study of the impact of salinity on the growth of perch young-of-the-year (YOY) was performed to test the hypothesis that a brackish environment positively influences percids. Field observations revealed that body length, condition factor, fatness coefficient and fat content in muscles were significantly higher in individuals inhabiting the cooler, brackish waters of the Baltic Sea than in individuals inhabiting the Curonian Lagoon. A positive effect of low salinity on growth was also established in the experimental study. Hence, the study results suggest that under certain temperature conditions, brackish waters beneficially affect the growth of pikeperch and perch. [ABSTRACT FROM AUTHOR]

Recruitment of perch (Perca fluviatilis) and pikeperch (Sander lucioperca) was studied in two bays and an estuary in the Baltic Sea during 1982 and 1993. For both species, year-class strength began to correlate positively with water temperature one month after the assumed hatching. Recruitment was estimated as relative year-class strength at the adult stage, and water temperature as degree-day sums over 10 °C. Temperature-corrected age-0 littoral catches imply that year-class strength is determined in early summer. The results, thus, suggest similarities in the recruitment of perch and pikeperch. [ABSTRACT FROM AUTHOR]