Fischlarven der westlichen Ostsee – Biodiversitätsuntersuchungen von 2000 bis 2005

Fish larvae surveys provide information on the species composition in an area of investigation and leads to a better understanding of the entire fish community. Since 2000 every year in April/May an ichthyoplankton survey in ICES-Subdivision 22 and 24 has been performed to sample the plankton community in the western Baltic Sea. One objective was to acquire indicators of possible changes in the natural structures of the fish community. The time series derived from the Bongo-Net samples is too short to show a trend in larval densities. Up to now samples in the western Baltic Sea yielded only low mean densities. According to the reproductive biology the fish species were divided in three major groups: -Fish species with a long developmental phase in the plankton community -Small short living species with benthic eggs and a reduced planktonic phase -Guests without local spawning populations Species were identified, which were absent in the plankton of the western Baltic Sea in the 1960s and 1970s.

Untersuchungen zur chemischen Zusammensetzung und Nematodenbelastung von Stinten (Osmerus eperlanus L.)

Smelt (Osmerus eperlanus L.) from the river Elbe has a long tradition as local food speciality. It is offered baked or fried every year during spring in many restaurants along the river. Information about the composition of the edible part and its changes during fishing season are scarce. In earlier days the fish was mostly sold by local fisherman directly after catch. Today the fish is also offered as ungutted fresh fish in ice on the whole sale market. The freshness of this fish has not been studied. Smelt from the river Elbe is known to contain nematode larvae (Pseudoterranova decipiens) in the muscle meat. Actual quantitative data on the abundance and prevalence in the commercially offered ice stored fish are missing.

Veränderungen der Farbe und thermischen Stabilität der Muskelproteine von Räucherforellen während der Kühllagerung

The aim of the investigation was to prove if different farming conditions like conventional and organical farming of rainbow trout may cause differences in quality which are detectable by physical methods such as colour measurement and differential scanning calorimetry. Colour measurement revealed remarkable differences in lightness. Smoked trouts originating from conventionally farmed fish were much lighter than those of organically farmed trouts. This difference in L* could already be found when colour measurements were taken on the raw material. However, during chilled storage differences were equalized. Redness and yellowness were not significantly influenced by farming and did not change remarkably during chill storage. Based on earlier investigations on changes in thermal stability caused by heating, DSC curves of smoked trout could be used to verify that the core temperature of smoked fish had reached at least 60 °C during hot smoking process. This temperature is demanded by the guidelines of the German Food Code. In the DSC curves only the actin peak was still visible. All other proteins were obviously denatured during the hot smoking. When DSC curves were taken from smoked trout after different durations of chilled storage it could be seen that the denaturation temperature of actin decreased almost linearly with progression of storage time.

Nachweis von Parvalbuminen in Störgeweben

Parvalbumins, calcium-binding, heat-stable proteins of considerable allergenic potential, are occurring in high concentration in light muscle of many fish species. Lack of knowledge about parvalbumins in sturgeon tissues prompted us to study the distribution of this type of proteins in light and dark muscle, as well as in swim bladder and skin of Atlantic sturgeon, Acipenser oxyrhynchus, and three other sturgeon species. Results: Light and dark muscle of sturgeons contained water soluble proteins with following properties: (1) Great stability against heating at 70 or 80 °C. (2) Isolelectric points between 3.85 and 5.66. (3) Treatment of proteins separated by isoelectric focusing with the dye “stains all” gave blue protein bands. (4) The molecular mass was about 10 to 14 kDalton. (5) Concentration of acidic, heat-stable proteins was higher in light than in dark muscle. Taken together, these findings gave strong indication for the presence of parvalbumins in muscle tissue of sturgeons. This conclusion was corroborated by immunological tests. However, parvalbumin could not be detected in swim bladder tissue. Skin preparations showed only traces of parvalbumins, possibly resulting from residual muscle tissue.

Population dynamics of the skipjack tuna (Katsuwonus pelamis) of the Eastern Pacific Ocean

ENGLISH: Catches of skipjack tuna supporting major fisheries in parts of the western, central and eastern Pacific Ocean have increased in recent years; thus, it is important to examine the dynamics of the fishery to determine man's effect on the abundance of the stocks. A general linear hypothesis model was developed to standardize fishing effort to a single vessel size and gear type. Standardized effort was then used to compute an index of abundance which accounts for seasonal variability in the fishing area. The indices of abundance were highly variable from year to year in both the northern and southern areas of the fishery but indicated a generally higher abundance in the south. Data from 438 fish tagged and recovered in the eastern Pacific Ocean were used to compute growth curves. A least-squares technique was used to estimate the parameters of the von Bertalanffy growth function. Two estimates of the parameters were made by analyzing the same data in different ways. For the first set of estimates, K= 0.819 on an annual instantaneous basis and L= 729 mm; for the second, K = 0.431 and L=881. These compared well with estimates derived using the Chapman-Richards growth function, which includes the von Bertalanffy function as a special case. It was concluded that the latter function provided an adequate empirical fit to the skipjack data since the more complicated function did not significantly improve the fit. Tagging data from three cruises involving 8852 releases and 1777 returns were used to compute mortality rates during the time the fish were in the fishery. Two models were used in the analyses. The best estimates of the catchability coefficient (q) in the north and south were 8.4 X 10- 4 and 5.0 X 10- 5 respectively. The other loss rate (X), which included losses due to emigration, natural mortality and mortality due to carrying a tag, was 0.14 on an annual instantaneous basis for both areas. To detect the possible effect of fishing on abundance and total yield, the relation between abundance and effort and between total catch and effort was examined. It was found that at levels of intensity observed in the fishery, fishing does not appear to have had any measurable effect on the stocks. It was concluded therefore that the total catch could probably be increased by substantially increasing total effort beyond the present level, and that the fluctuations in abundance are fishery-independent. The estimates of growth, mortality and fishing effort were used to compute yield-per-recruitment isopleths for skipjack in both the northern and southern areas. For a size at first entry of about 425 mm, the yield per recruitment was calculated at 3 pounds in the north and 1.5 pounds in the south. In both areas it would be possible to increase the yield per recruitment by increasing fishing effort. It was not possible to assess potential production of the skipjack stocks fished in the eastern Pacific, except to note that the fishery had not affected their abundance and that they were certainly under-exploited. It was concluded that the northern and southern stocks could support increased harvests, especially the latter. SPANISH: Las capturas de atún barrilete que sostienen las pesquerías principales de la parte occidental, central y oriental del Océano Pacífico han aumentado en los últimos años; así que es importante examinar la dinámica de la pesquería para determinar el efecto que pueda tener sobre la abundancia de los stocks. Se desarrolló un modelo hipotético, lineal para standardizar el esfuerzo de pesca a un solo tamaño de barco y tipo de arte. Luego se usó el esfuerzo standardizado para computar un índice de la abundancia que pueda dar razón de la variabilidad estacional en el área de pesca. Los índices de la abundancia variaron mucho de un año a otro tanto en el área septentrional como en el área meridional de la pesquería, pero indicaron una abundancia generalmente superior en el sur. Se emplearon los datos de 438 peces marcados y recuperados en el Océano Pacífico oriental para computar las curvas de crecimiento. Una técnica de mínimos cuadrados fue usada para estimar los parámetros de la función de crecimiento de van Bertalanffy. Se hicieron dos estimativos de los parámetros mediante el análisis de los mismos datos, de diferente manera. Para el primer juego de estimativos, K=0.819 sobre una base anual instantánea y L∞=729 mm; para el segundo, K=0.431 y L∞=881. Estos se correlacionaron bien con los estimativos obtenidos usando la función de crecimiento de Chapman-Richards, que incluye la de von Bertalanffy como un caso especial. Se decidió que la última función proveía un ajuste empírico, adecuado a los datos del barrilete, ya que la función más complicada no mejoró significativamente el ajuste. Los datos de marcación de tres cruceros incluyendo 8852 liberaciones y 1777 retornos, fueron usados para computar las tasas de mortalidad durante el tiempo en que los peces estuvieron en la pesquería. Se usaron dos modelos en los análisis. Los mejores estimativos del coeficiente de capturabilidad (q) en el norte y en el sur fueron 8.4 X 10-4 y 5.0 X 10-5 , respectivamente. La otra tasa de pérdida (X), la cual incluyó pérdidas debidas a la emigración, mortalidad natural y mortalidad debida a llevar una marca, fue 0.14 sobre una base anual instantánea para las dos áreas. Con el fin de descubrir el efecto que posiblemente pueda tener la pesca sobre la abundancia y el rendimiento total, se examinó la relación entre la abundancia y el esfuerzo y entre la captura total y el esfuerzo. Se encontró que a los niveles de la intensidad observada en la pesquería, la pesca no parece haber tenido ningún efecto perceptible en los stocks. Por lo tanto se decidió que mediante un aumento substancial del esfuerzo total, más allá del nivel actual, la captura total probablemente podría aumentarse, y que las fluctuaciones de la abundancia son independientes de la pesquería. Los estimativos del crecimiento, mortalidad y esfuerzo de pesca fueron usados para computar las isopletas del rendimiento por recluta del barrilete, tanto en las áreas del norte como del sur. Para una talla de primera entrada de unos 425 mm, el rendimiento por recluta fue calculado en 3 libras en el norte y 1.5 libras en el sur. En ambas áreas sería posible aumentar el rendimiento por recluta mediante un aumento del esfuerzo de pesca. No fue posible determinar la producción potencial de los stocks del barrilete pescado en el Pacífico oriental, excepto para observar que la pesquería no ha afectado su abundancia y que ciertamente se encuentran subexplotados. Se concluyó que los stocks norte y sur pueden soportar un aumento en el rendimiento, especialmente este último. (PDF contains 274 pages.)

Maifische an der deutschen Nordseeküste - zum Auftreten von Finte (Alosa fallax) und Alse (Alosa alosa)

Quantitative data on twaite shad are collected annually in spring and autumn since 1974 by the Demersal Young Fish Survey. Results for occurrence of these anadromous species show that twaite shad has been caught in the entire Wadden Sea area despite of the poorly suited 3-m shrimp beam trawl applied in the survey. Regional differences occur: Only sporadic catches are observed in the northern part of the German Wadden Sea, while more frequent ones occurred southwards and in the East Frisian Islands region. The obvious recent increase of abundance of Alosa fallax in spring allows for a lower ranking in the Red List of Endangered Species, while Allis shad (Alosa alosa) requires the same classification, as it was the never caught during the thirty years of surveys.

Die Reproduktion von Dorschen (Gadus morhua L. und Gadus morhua callarias L. ) in der Ostsee unter besonderer Berücksichtigung der Arkonasee. Teil I: Allgemeiner Verlauf des jährlichen Reifeprozesses und der Laichaktivitäten in den verschiedenen Gebieten

From 1993 to 2003 special surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea. The ICES advice for cod in the Baltic Sea is based on yearly stock assessments of two separate stocks the western (SD 22 – 24) and the eastern stock (SD 25 – 32). Both stocks are characterized by different spawning seasons. The general progression of the maturity suggests that two types of development can be distinguished. In the western Baltic Sea (SD 22) the maturity development is temporal stable, with a relative short, main spawning period from March to April - spring spawner. In the Arkona Sea and Bornholm Basin the main spawning season starts in June and probably finishes in September - summer spawner. The proportion of spawners in summer is significantly higher than in spring in the Arkona Sea and Bornholm Basin. This again underlines the importance of the Arkona Sea for the reproduction success of the eastern Baltic cod stock. The analysis furthermore show, that the proportion of male spawners was significantly higher than the proportion of female spawners in all areas and the investigated months. This observation suggests that the reproductive success is only limited by the number of female cod which participates in the spawning process.

Die Reproduktion von Dorschen (Gadus morhua L. und Gadus morhua callarias L.) in der Ostsee unter besonderer Berücksichtigung der Arkonasee. Teil II: Statistische Analysen zum Anteil reproduktiv aktiver Dorsche in Bezug auf gebietsspezifische Unterschiede und Gemeinsamkeiten, sowie deren mögliche Ursachen.

Surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea from 1993 to 2003. Part I of the article describes the general maturity development and the spawning activities in the western Baltic Sea, the Arkona Sea and the Bornholm Sea. The studies suggest that two types of spawner can be distinguished, the spring spawner in the western Baltic Sea and the summer spawner in the Arkona Sea and the Bornholm Basin. The descriptive analysis is supported by statistical studies presented in this article. It is shown, that the proportion of spawning individuals is significantly higher in summer than in spring in the ArkonaSea and the Bornholm Sea. Furthermore, it is shown that reproductive mixing of both types of spawner is possible in the Arkona Sea in May/June due to the hydrographical conditions in the Arkona Sea which were suitable in 8 of 10 years for successful reproduction of both Baltic cod stocks, and that spatial expansion of spawning activities of the eastern Baltic cod stock into the Arkona Sea is positive correlated with the size of spawning stock in the Bornholm Sea.

Wirkungsbezogene Detektion von toxischen Substanzen in Fisch und Umwelt

The detection of unknown and the quantification of known toxic substances is a challenge for the modern chemical and biological analysis. Effect-related in vitro methods, e.g. AH-receptor or estrogene-receptor mediated, offer some advantages compared to the classical chemical analysis. It could be shown that two cell lines exhibit different sensitivities to 2,3,7,8-tetrachlorodibenzodioxin (TCDD), although the cells contain the identical dioxin-receptor. The application and limitations of these methods in envi-ronmental analysis are discussed.

Horizontale Trennblätter in Trawls zur Verringerung von Discards in der Ostsee

A primary objective of the Common Fishery Policy of the European Union is the reduction of discards and unwanted by-catches in the fishery. In principle this could be achieved if the catching methods were optimised for this. Still high numbers of undersized flatfish are caught in the bottom trawls. Although EU regulations make the use of the BACOMA codend mandatory in the Baltic Sea cod areable to escape through square mesh escape window of the BACOMA net the whereas flatfish still remain in the cod-end. Gear experiments have been carried out with the aim to better separate cod from the flatfish fraction already when entering the rear belly, making use of the natural behaviour of the fish, i. e. the preferred swimming distance from the bottom of the net in the funnel. As cod have a natural tendency to keep a relativly great distance from the bottom, flatfish tend to stay close to it. It was attempted to separate both fractions by splitting the funnel into an upper and lower part with a horizontal panel. This wastested for two different nets, a cod trawl to separate cod from flatfish, and an eel-trawl to separate cod and flatfish from eel. Cod and flatfish separation is best at a panel distance of 50 cm from the bottom. Thus, 74 % of the cod were found in the upper panel, whereas 75 % of the flounder were in the lower section. A separation of eel from cod was however not possible, since eel tend to rise to the upper part of the net, together with cod.

Die Anwendung molekulargenetischer Verfahren in der fischereiwissenschaftlichen Forschung - Trennung von Fischpopulationen

The discrimination of stocks and separate reproductive units within fish species to facilitate fisheries management based on biological data has always been a challenge to fisheries biologists. We describe the use of three different molecular genetic techniques to detect genetic differences between stocks and closely related species. Direct sequencing of the mitochondrial ND3 gene describes the relationship between different aquaculture strains and natural populations of rainbow trout and revealed genetic homogeneity within the hatchery strains. Microsatellite analyses were used to explore the differences between redfish species from the genus Sebastes and to verify populations structure within S. mentella and S. marinus. This lead to an un equivocal discrimination of the species and an indication of populations structure within those species in the North Atlantic. The Amplified Fragment Length Polymorphisum (AFLP) methodology revealed genetic differences between Baltic and North Sea dap (Limanda limanda)and a possible population structure within the North Sea.

Der PAH-Metabolit 1-Hydroxypyren in der Galle von Klieschen (Limanda limanda) aus Nord- und Ostsee

Due to their carcinogenic properties, polycyclic aromatic hydrocarbons (PAH) are important environmental contaminants which may lead to increased levels of neoplastic aberrations in fish liver. To measure the PAH contamination of fish, concentrations of PAH metabolites were determined in the bile. The main metabolite 1-hydroxypyrene was determined in concentrations from < 0.8 to 189 ng/ml in bile of dab caught in the North Sea and the Baltic Sea re-spectively. The concentrations are comparable to levels of 1-hydroxypyrene measured in cod and herring from the Baltic Sea. The highest concentrations in dab bile were measured in fish from the inner German Bight and the Kiel Bight.

Die Qualitäts-Index-Methode (QIM), ein verlässliches Instrument zur sensorischen Bewertung der Frische von Fisch

Fish research institutes in Europe have made considerable effort in developing rapid, objective sensory methods for evaluation of fish freshness. The Quality Index Method(QIM) has been recommended for a European initiative regarding standardisation and harmonisation of sensory evaluation of fish. QIM-schemes have been developed for various common European fish species. Research has now provided the industry with a convenient, objective and powerful tool for measuring freshness of fish kept in ice Further research is needed to evaluate the applicability of QIM for fish handled, stored and processed under different conditions. However, for progress and development of QIM it is now very important that the fish sector implements QIM in fish auctions and the quality management system of the fish processing plants.

Einfluss von Reifung und technologischen Behandlungen auf die Proteine des Rogens von Regenbogenforellen (Oncorhynchus mykiss)

The use of differential scanning calorimetry for investigating the yolk proteins of the roe of rainbow trout allows to monitor the influence of maturation and vitellogenesis which modifies the DSC curves with regard to transition temperature and enthalpy. Two endothermic peaks become more and more pronounced with increasing maturation of the roe. However, it is still not known which protein fraction is represented by each of the peaks. DSC curves of yolk protein depend on fish species. They are also influenced by technological treatments. Further investigation is necessary to discover whether or not yolk proteins of other fish species are influenced in the same manner by maturation and vitellogenesis and which protein fraction represent the individual peaks.

Untersuchungen zur Aufzucht von Barramundi

Lates calcarifer (Barramundi) ist ein naher Verwandter des bei uns inzwischen seit Jahren bekannten und auf vielen Wochenmärkten zu findenden Viktoriabarsches(Lates niloticus), dem er auch im Aussehen ähnelt. Das Verbreitungsgebiet dieses euryhalinen Fisches sind die Küstenregionen mitsamt ihren Flußgebietssystemen des nördlichen Indischen und des westlichen tropischen Pazifischen Ozeans. Bei einer derartigen weiten Verbreitung ist es nicht verwunderlich, daß sich viele Bestände ausgebildet haben, die durchaus unterschiedliche Leistungen z. B. in Hinblick auf die Reproduktionsbiologie zeigen.