Experimente über die Wirkung von UV-B auf pelagische Fischembryonen in einem Sonnenscheinsimulator

One of the supposed effects of the observed ozone depletion is the increase of solar UV-B irradiation at the seasurface. This will cause an impact on certain compartments of marine ecosystems. Especially, sensitive developmental stages of pelagic fish embryos might be affected. Embryos of dab (Limanda limanda) and plaice (Pleuronectes plalessa) were experimentally exposed 10 different amounts of UVB irradiation in a sunshine simulator. This programmable device allows the dosage of realistic solar irradiation in quality and guantity. Experiments were carried out in March 1995 and February 1996. Either artificially inserninated and reared emhryos of dab and plaice or embryos caught in the German Bight were exposed to simulated solar irradiation. The 1995 experiments served to identify the effective irradiation dosages. For the 1996 experiments irradiation applied was much lower, being dose to realistic valucs expected over the North Sea as a consequence of ozone depletion. The following end points were studied: 1. Mortality, 2. sublethal morphological effects (malformations), 3. DNA damage, 4. changes in buoyancy of embryos measured as changes in osmolarity of the perivitelline fluid. Conditions for the simulation of daylight were a c1oudless sky with a solar zenith distance of 34 % (air mass 1.2). The adopted ozone depletion was 40 % corresponding to 180 DU (Dobson Units) instead of 300 DU. In the 1995 experiments time and dosage dependent influenccs on mortality and buoyancy of embryos of dab and plaice were found. Even in those embryos which were protected from the UV-B spectral range a loss of buoyancy was registered after 12 hours in the simulator. No diffcrences in DNA integrity as determined by DNA unwinding of exposed and control embryos were found. Also with lower amounts of irradiation in the 1996 experiments dosage dependent acute mortality, malformations, and impact on the buoyancy of the emhryos was registered. Sublethal effects occurred as well in embryos protected against UV-B in the exposure chambers, but were not found in the dark controls. The impact of low dosages of UV-B on the buoyancy of pelagic fish embryos might indicate an important ecological threat and deserves further studies.

Einfluß der Holtechnologie auf die Selektion von Grundschleppnetzen

A widespread belief among fishermen that sidetrawlers show a better selectivity than sterntrawlers was investigated in a comparative fishing exercise in the Baltic. In contrary to earlier observations during this experiment in May no essential differences with regard to the selectivity of the trawls used could be found for both types of fishing vessels. Possible explanations for the result are discussed.

Haltbarkeit von Nordsee-Wittling (Merlangius merlangus) bei Lagerung in schmelzendem Eis

North-Sea whiting shows a much shorter shelf life in melting ice than other gadoid fishes like saithe, cod and haddock. It can be stored for a maximum of 14 days in ice before being rated as unfit for human consumption. Appropriate freshness indicators for whiting are: sensory tests, dimethylamine- and trimethylamine oxide-nitrogen, creatine content. Of most value for whiting is the determination of thc electric resistance by the fishtester VI.

Bewertung von Frische- und Verderbsindikatoren bei der Eislagerung von Schollen (Pleuronectes platessa)

An iced storage experiment with plaice was conducted during the 1l5th cruise of FRV "Walther Herwig II" in the North Sea. Iced stored plaice were rated by sensory methods as saleable until day 18 of iced storage and as edible until day 20. In addition to the sensory tests the Fischtester VI readings and the pH-value measured in muscle homogenate proved to be useful freshness indicators, while TVB-N is a typical spoilage indicator.

Untersuchungen zur Aufzucht von Dorschen (Gadus morhua morhua) der Westlichen Ostsee. Teil II: Aufbau und Hälterung eines Laichfischbestandes sowie Erbrütung der gewonnenen Eier

In 1993 and 1994 hatching and rearing of cod eggs and larvae from the western stock was carried out aiming at data about the reproduction biology of this species. This paper describes the hatching methods and first results of the correlation between various biotic and abiotic factors, naturally fertilized eggs from a broodstock, and the amount of viable larvae.

Einfluß von Anlagen der Offshore-Industrie auf die Fischerei in der Nordsee

From the beginning of the oil and gas exploration in the North Sea the impact of offshore installations, especially pipelines, on the fishery has been thoroughly discussed and investigated. Since fishing activities in the vicinity of pipelines are not prohibited, special precautions have to be taken to prevent towed fishing gear from being fouled by a pipeline. Until now all recommendations for the installation of pipelines are based on the results of tests with trawls crossing one pipeline. New problems will arise if parallel pipelines are installed as planned in the near future.

Zum Auftreten von Geruchs- und Geschmacksabweichungen ("Tainting") bei Frühjahrsheringen (Clupea harengus) aus der Ostsee

An account of the occurrenee of tainting in fish and seafood with special consideration of spring spawning herring from the Baltic Sea (estuary of the river Oder) is given. About 26 % of the herring samples examined by sensory methods showed tainting. In general the intensity of taint was weak or moderate and weaker as observed years ago. Also in fishery products (pickled herring, deep fried herring in marinade) processed from tainted herrings the same or a similar sensory intensity of taint as in the raw material was observed. The source of taint is not dear. A pollution with halogenphenols from the sea water could be possible. In further investigations we will monitor the further development and try to identify the tainting compounds.