Clupea

Abstract: The effect of chitosan with different molecular weights as coatings for shelf-life extension of fresh fillets of Atlantic cod (Gadus morhua) and herring (Clupea harengus) was evaluated over a 12-da...

Abstract: Fish protein hydrolysates were prepared, using minced fillets and Al-calase and papain, from raw herring and from herring defatted by ethanol extraction, cooking and pressing. Physicochemical, sensory and storage properties as well as the molecular weight sizes in spraydried hydrolysates were evaluated. Fat extraction before hydrolysis reduced degree of hydrolysis. Alcalase hydrolyzed samples to a higher degree than papain. Ethanol extraction reduced fishy odor to barely detectable levels. Papain hydrolysates were more bitter than those made with Alcalase. Color and nonenzymic browning measurements indicated darkening during 3 mo storage at room temperature (∼20°C).

Abstract: Two opposing concepts of Atlantic herring, Clupea harengus L., population structure are critically reviewed with the objective of unifying these divergent views under the metapopulation concept. It is concluded that neither the discrete population concept nor the dynamic balance concept adequately explains all the data associated with herring population structure and dynamics, including meristic and morphometric measurements, life- history traits, homing, year-class twinning, and biochemical analyses. However, the available information does suggest that Atlantic herring population structure and dynamics are well described within the metapopulation concept. The example of sympatric seasonal-spawning populations is used to illustrate the strategy, opportunity and mechanism by which local population integrity and persistence are maintained within the adopted- migrant hypothesis. Local population integrity is maintained through behavioural isolation, i.e. repeat rather than natal homing to spawning areas, while local population persistence is ensured through the social transmission of migration patterns and spawning areas from adults to recruiting individuals

Abstract: We used stable nitrogen isotopes to describe the pelagic food-web structure of three coastal Baltic Sea areas, each of which was sampled twice. Two of the areas were influenced by 15N-rich nutrient discharges from a sewage treatment plant. Analyses were made of particulate organic matter (<35 μm, mainly phytoplankton), zooplankton, mysids (Mysis mixta and M. relicta), sprat (Sprattus sprattus), smelt (Osmerus eperlanus), four size classes of herring (Clupea harengus), and pikeperch (Stizostedion lucioperca). Discharges from the sewage treatment plant significantly increased δ15N values in the whole food web, from phytoplankton to piscivorous fish. Based on nitrogen isotopic compositions, consistent trophic food-web structures were observed on both occasions and in all three areas. The results indicate that zooplankton and mysids may have more complex diets than assumed before. Apparent trophic fractionation, i.e., differences in δ15N between a consumer and its assumed food, averaged 2.4‰ with a standard e...