Assessment of burbot Lota lota (L. 1758) population sustainability in central European reservoirs.

A novel sampling scheme, using a combination of electrofishing, visual exploration by scuba divers, two types of fyke nets and longlines, was tested in four reservoirs (including their inlets and outlets) to monitor a population of burbot Lota lota. This was supplemented by fry trawling and vertical hydro-acoustics, to detect L. lota larvae in two deep reservoirs that have had a long-term stocking programme. The majority of the L. lota detected were juveniles, captured by electrofishing in the littoral zones of the reservoirs and in running waters. Older individuals were rarely captured with longlines or fyke nets in deeper zones or structured habitats within the reservoirs. A combination of multiple sampling methods provided an assessment of the whole population. Population establishment could not be demonstrated as the age structure of the sampled fish corresponded with that of the stocked fish. Low post-stocking survival, migratory behaviour, interactions with other species and warmer water temperatures are considered the potential drivers for unsuccessful establishment of L. lota populations in these reservoirs.

Planktonic or non-planktonic food in young-of-the-year European perch Perca fluviatilis in ponds.

Higher biomass especially of some aquatic macrophyte species offered a higher density of phytophilous zoobenthos, but did not increase the proportion of non-planktonic to planktonic prey in young-of-the-year perch Perca fluviatilis. Both abundance and biomass of non-planktonic prey dominated over planktonic prey in the pond with lower biomass of aquatic macrophytes and lower food. Survival of P. fluviatilis was lower (20%) in the pond with lower food than in the other pond (34%), however, specific growth rate (1.3% day(-1) ) and final Fulton's condition factor of P. fluviatilis were similar in both ponds.

Occurrence of age-0 year dwarf pikeperch Sander lucioperca in late summer--an overlooked phenomenon in reservoirs.

Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutch reservoir revealed extremely small age-0 year pikeperch Sander lucioperca (mean 24 mm standard length, LS , minimum 13 mm LS ) alongside more normal-sized S. lucioperca that are found at the end of the first growing season (mean 50 mm LS ), resulting in two clearly size-separated cohorts. Reference to such small age-0 year S. lucioperca in lakes or reservoirs at this time of year and in such large numbers are almost absent the scientific literature, and the presence of these small S. lucioperca is contradictory to the common understanding of the reproductive biology of this species. This overlooked phenomenon may have a major effect on the population dynamics of this valuable species because of size-dependent winter mortality.

Biogenic amines in silage. 3. The occurrence of six biogenic amines in farm-scale grass and maize silages.

Concentrations of putrescine (PUT), cadaverine (CAD), spermidine (SPD), spermine (SPM), histamine (HIS) and tyramine (TYR) in 53 grass silages and 54 maize silages were determined using an HPLC method. Concentrations of all amines excluding SPD in grass silages decreased significantly with increasing dry matter (DM) contents and decreasing acetic acid concentrations. The mean concentrations were 1310, 642, 414, 139, 120 and 33.6 mg/kg for TYR, CAD, PUT, SPM, HIS and SPD respectively in grass silages of 20-30% DM. The maximal values found were twice to five times higher than the mean values. The effect of increasing DM on the amines concentrations was not evident in maize silages. The mean concentrations, regardless of the DM content, were surprisingly high: 435, 388, 341, 71.7, 25.1 and 5.4 mg/kg for TYR, PUT, CAD, HIS, SPD and SPM. The maximal values in maize silages were three times to ten times higher than the mean values. Considering that maize silage forms the great proportion of the diets of cattle during long-term winter feeding, further toxicological and physiological research should be carried out.

Criteria for quantitative schlieren interferometry.

An evaluation is made of a criterion suggested by Temple for the size and location of obstacles in the focal plane of a schlieren interferometer. Measurements of the thermal distributions near a heated vertical plate and near a heated horizontal cylinder are presented. The results of previous experiments are discussed; the results of new experiments are reported. It is concluded that, unless the criterion is satisfied, the resulting fringe systems will not give the correct quantitative results.