Diet of the twaite shad Alosa fallax (Lacépède, 1803) (Clupeidae) in the Gulf of Gdansk, the Baltic Sea

Twaite shad Alosa fallax (12–48 cm total length) from the Gulf of Gdansk feed on Mysids: Mysis mixta, Neomysis integer, and fish: Sprattus sprattus, Osmerus eperlanus, and Pomatoschistus sp.. In the stomachs of A. fallax there also occur Hydrobia sp., Diptera and small stones, particles of wood and plastic. The food of inshore twaite shad measured from 12 to 21 cm centered on M. mixta. Fish are the main prey for A. fallax from the class length 22–31 cm from the Vistula River mouth and for all shads longer than 32 cm.

Seasonal changes in the lipids of Mysis mixta (Mysidacea) from the hyperbenthos of a cold-ocean environment (Conception Bay, Newfoundland)

Total lipid (TL) and lipid class composition of Mysis mixta Lilljeborg from 240-m depth in a cold-water marine bay were studied throughout 1999 and 2000. The objective was to relate the seasonal lipid dynamics in an abundant and lipid-rich hyperbenthic species to its life cycle and to the annual phytoplankton bloom. Mysis mixta accumulated high levels of lipid reserves similar to those reached by other cold-water zooplankton. Greatest accumulation occurred in maturing females and males upon initiation of the spring bloom and continued for 6 months. The lowest TL level was ~5% dry mass (DM) in small juveniles, post-spawned males, and spent females, and the highest level was 32% DM in females approaching full maturity (overall content range 0.3–16 mg·mysid–1). Most females accumulated lipid for 2 years before spawning, although a few females spawned 7 months early with a very low TL content. Seasonal variation in TL resulted primarily from net changes in triacylglycerol, the predominant neutral lipid. Seasonal and interannual variation in TL quantities in individuals and in areal concentrations of lipid in the hyperbenthic population indicates a strong trophic link between M. mixta and the pelagic production cycle.

Feeding preferences of herring (Clupea harengus) and sprat (Sprattus sprattus) in the southern Baltic Sea

No field studies have been performed on the selectivity of herring and sprat in the southern Baltic Sea in relation to their entire range of prey. Accordingly, we tested in the field the following hypotheses: (i) sprat and herring are selective feeders and (ii) sprat and herring selectivity is size- and season-dependent. The results show that (i) smaller herring and all size classes of sprat are strictly zooplanktivorous, selecting principally Temora longicornis and Bosmina maritima during the autumn and Pseudocalanus elongatus in winter; (ii) larger herring are essentially nektobenthos feeders, predating on Mysis mixta during the autumn and amphipods and polychaetes during the winter; and (iii) herring and sprat seem to avoid Acartia spp. in both autumn and winter. During the autumn, herring are zooplanktivorous up to 18–20 cm, whereas in winter herring feed on nektobenthos starting from 14–15 cm. Selectivity was not an absolute process but it was related to prey relative abundance in the sea and, possibly, to prey profitability (e.g. size, conspicuousness, and reaction time).