Quantitative expressions are presented to describe the effects of temperature and food concentration on stage duration and growth rate of Temora longicornis for each of the model stage groups (N1–N6 – naupliar stages, C1, C2, C3, C4, C5 –the five copepodid stages). The calculations were made on the basis of experimental data from the literature for T. longicornis from the south-eastern and the southern North Sea. Relationships were obtained between the growth parameters and temperature for the 5–10◦C temperature range and food concentrations from 25 mgC m−3 to excess. Also computed was the total mean development time as a function of the above-mentioned parameters, temperature and food availability. The simulations computed here are similar to the experimental results. The growth rates for successive stages were obtained according to the correction of the ‘Moult Rate’ method, which allows the use of mean weights and stage durations. The calculations also suggest that three complete generations of T. longicornis from the Gdańsk Deep (the southern Baltic Sea) can develop during a single year.
The abundance of the sardine in the North Sea suddenly increased after 1995. Since 2002, the sardine has been spawning regularly in the German Bight, and all its life stages can be found in the area. The larval feeding ecology of two small pelagic clupeiform species with very similar life histories was investigated, the particular aim being to determine signs of food overlap. The distribution and feeding of sprat and sardine larvae were investigated during late spring 2003 on two transects covering a wide range of environmental conditions in the German Bight. Larvae co-occurred at all the stations investigated. Sprat and sardine larvae shared a wide range of prey types. Gut fullness and feeding success were similar in both species; however, potential food competition is avoided to some extent by different habitat preferences.
The concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (DL-PCB) were determined in samples of Baltic herring (Clupea harengus membras) and sprat (Sprattus sprattus balticus) in 2006 from commercial catches in Estonian coastal waters, Baltic Sea. The dioxin content of the fish sampled in 2006 did not exceed the European Union’s maximum permissible level for PCDD/Fs (4.0 pg WHO -TEQ/g fresh weight) and for the sum of PCDD/Fs and DL-PCBs (8.0 pg WHO -TEQ/g fresh weight). PCDD/Fs and the sum of PCDD/Fs and DL-PCBs content in herring were 2.12 and 3.84 pg WHO-TEQ/g of fresh weight respectively; the corresponding figures for sprat were 1.94 and 3.82 pg WHO-TEQ/g of fresh weight. Comparable with our earlier data on the content of dioxins in three to four year old herring and two to three year old sprat, these data show that two servings of fish per week are not at all harmful to the health of the Estonian people; indeed, the opposite is more likely to be the case.
Background. Natural antioxidants become increasingly important in fish processing and particularly in the preservation phase of fish raw materials. Some of them can protect lipids, containing essential unsaturated fatty acids. The aim of the present study was to determine antioxidant properties of aqueous extracts of rosemary and sage, compared with the activity of BHA (butylated hydroxyanisole) and Endox in lipids of fresh Baltic fishes (herring, sprat, flounder) and those subjected to frozen storage at -25°C for 6 months. Materials and Methods. Antioxidant activity of the additives was determined based on β-carotene changes in fish lipids after 10, 20, 40, and 60 min of heating at 50°C. Results. The plant-origin extracts and the synthetic antioxidants used, inhibited most extensively β-carotene changes in the lipids of non-frozen herring. They were the least effective in non-frozen sprat lipids. The frozen storage lowered the antioxidant action of the additives in relation to β-carotene in lipids of herring and flounder, whereas in sprat lipids the antioxidants used, continued their protective action for β-carotene, during heating. Elongation of the heating time from 10 to 60 min increased the β-carotene losses and their pace followed the logarithmic scale. The activity of the antioxidants in fish lipids decreased along with the increase of polyunsaturated fatty acids (C20 : 5, C22 : 5, and C22 : 6) contents Conclusion. The antioxidant properties of plant-origin additives and synthetic antioxidants decreased along with the increased content on unsaturated fatty acids of fish lipids. Six-month-long frozen storage of the fish raw materials resulted in a decrease of the protective properties of the additives used, in relation to the lipids of Baltic herring and flounder. The best protective properties for lipids of flounder and sprat exhibited Endox, while aqueous extract of rosemary was the most effective in relation to sprat lipids.
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