Studies on temperature effects during incubation of embryos of sea trout (Salmo trutta L.), vendace (Coregonus albula L.), common whitefish (Coregonus lavaretus L.), pike (Esox lucius L.), ruffe (Gymnocephalus cernuus L.), and rudd (Scardinius erythrophthalmus L.) showed optimal incubation temperatures to produce the highest percentage of newly hatched larvae at the best physical condition, of the highest weight and the highest total length, and carrying the smallest yolk sacs. At temperatures deviating from the optimum, an earlier hatching of much smaller larvae with larger yolk sac was observed. Higher rates of developmental malformations, the lower hatching success rate, and a marked reduction of mobility and activity of the larvae were also observed.

The carp juveniles were overwintered for 159 days (25 October 1997 – 31 March 1998) in cages placed in power station cooling water. The cages were stocked with carp fry of 163±20 g mean individual weight; the stocking density was 200 ind. cage-1, i.e., 100 ind. m-3. The experiment involved Dan-Ex 4,85 feed, an energy-rich extruded mixed feed. Depending on the treatment, the feed was offered daily and at 2-, 3-, and 4-day intervals. The daily feed ration amounted to 1% of the actual fish weight. During the following 28 days of spring culture (1-29 April 1998), the fish in all the treatments received the same feed offered at a daily ration of 1% of the actual fish weight. Feeding frequency was shown to have significantly affected body weight increments and chemical composition, both during overwintering and in the spring culture. The total body weight gain (TG) of the overwintered fish fed at 4-day intervals and those fed daily were 65.1 and 144%, respectively. During overwintering, feeding at 3-day intervals proved most advantageous. Compensatory growth was recorded in the initial two weeks of the spring culture in those fish that had not been fed daily during the preceding winter.

A total of 17 morphological characteristics, expressed as percentages of standard length (SL) of juvenile (23-83 mm SL) asp caught in Międzyodrze were examined. The lowest variability was typical of fork and total length and of the predorsal distance. The dorsal fin base length proved to be the most variable character. No pronounced changes in body proportions with increasing body length were observed.

Plastic (17) and meristic (3) characters of asp individuals caught at Międzyodrze were examined. A pronounced allometry in growth of the horizontal eye diameter, dorsal fin height, anal fin height, head length, maximum body depth, dorsal fin base length, and V-A distance was revealed. Statistically significant differences in body proportions between the asp fry (age group 0) and older individuals were found.

The paper summarises results of studies on reproductive potential of the pikeperch in the Polish part of the Vistula Lagoon. The length at which 50% of the females reach sexual maturity was determined as 41.8 cm l.t. The number of females present within 1989-2001 in the exploited population of the Vistula Lagoon pikeperch was estimated, as was the number of eggs laid each year. The estimated number of eggs laid during a year was found to range from 69 to 114 billion, the 9-yr annual average amounting to 52 billion. The highest numbers of eggs were laid by the Vistula Lagoon pikeperch females in 1989-1992. A high number of pikeperch egg found in a calendar year was not tantamount to the appearance of a numerous offspring. It was in short periods of time only that the two variables showed similar trends.

The presented studies aimed at the determination of the usability of experimental feed mixtures in the nutrition of Siberian sturgeon. Growth test was carried out on the fry of Siberian sturgeon with mean individual mass of 8.11 g·pc-1. The studies were carried out in controlled conditions in an aquarium hall in flow-outflow aquaria of 60 l capacity. Each aquarium was stocked with 12 pcs of fish. For the formation of experimental feeds prepared as isonitric and isocaloric diets, barothermal method (extrusion) was applied. In the feeds, blood isolates: plasma protein and meal of erythrocytes were used as fish meal substitutes on different substitution levels (0, 5, 10 and 15%). The feeds were evaluated on the basis of physical and chemical characteristics. Compositions of protein aminoacids and fatty acid profiles in lipides were identified in the feeds. In the final evaluation of the feeding tests, the following rearing effectiveness indices were used: Food Conversion Ratio (FCR), Specific Growth Rate (SGR), apparent Net Protein Utilization (aNPU) and Protein Efficiency Ratio (PER). Conclusions were drawn on the basis of statistical analysis using SAS computer program. Experimental results showed that the addition to the diets of blood preparations: plasma protein and meal of erythrocytes in 5, 10 and 15% proportions as replecement for 15% of fish meal did not cause improvement in the rearing of Siberian sturgeon fry.

Six extruded feed mixtures containig 0-35% of potato protein and designed for Siberian sturgeon were tested. A 50-day growth test was carried out using Siberian sturgeon fry of 3.59 g·pc-1 average individual mass. Study results explicitely indicated that potato protein is not useful in the nutrition of Siberian sturgeon. Increased participation of this component deteriorated visibly the feed utilization expressed by very low fish mass increments. Addition of potato protein exceeding 21% caused the occurrence of disturbances in the digestive processes of fish and increased mortality rate.

The results presented consist of data obtained from the analysis of sediment cores collected in March and July 1996 and in May 1997 from a sampling site located in the southern part of the Pomeranian Bay (Southern Baltic), in an area directly affected by freshwater discharge. The nematodes were identified to the genus level and assigned to appropriate trophic groups; changes in vertical distribution of nematode genera and trophic groups were followed as well. Nematodes were the major component of the meiobenthos at the study site, contributing more than 90% to the total meiobenthic abundance. The nematode abundance varied from about 1646 ind./10 cm2 (March 1996) to about 3452 ind./10 cm2 (July 1996). A total of 35 nematode genera were identified. Sabatieria was the most abundantly represented genus, accounting for from 23 to 32% of the total meiofaunal abundance and from 40 to 55% of that of the nematodes. The highest nematode genus richness was observed in the surficial sediment layers: 0-1cm (July 1996, May 1997) and in 2-3 cm (March 1996). The deeper sediment layers showed a clear reduction in nematode density, genus richness, and trophic diversity. The Sabatieria nematodes, representing the non-selective deposit feeders, were found to have penetrated the sediment to the deepest layers. Non-selective deposit feeders were found to dominate the nematode fauna throughout the period of study (60-80% of the total nematode abundance). The abundance of epistrate feeders and predators/omnivores increased in May 1997 and in July 1996, compared to March 1996, to about 20 and 11-16% of the total nematode abundance. The contribution of selective deposit feeders was low throughout the period of study (2-6% of the total nematode abundance). The results demonstrated the importance of freshwater discharge-associated sediment organic enrichment in the southern part of the Pomeranian Bay for the nematode taxocoene structure.

Of the 231 herring specimens caught in autumn from the Polish part of the Vistula Lagoon, 6.5% were found to contain III-stage Anisakis simplex larvae. The parasites were recorded in the fish longer than 23 cm. The presence of Anisakis simplex in autumn increases the risk of infection for accidental hosts, including humans.

The experiment, conducted from 13 December 1999 until 3 April 2000 at the Fisheries Experimental Station situated in the vicinity of the Dolna Odra power station at Nowe Czarnowo, involved 140+4 g mean individual weight carp aged 0+, kept in cages stocked at 100 ind. cage-1 (50 ind m-3) density. Six experimental treatments, each run in triplicate, were applied. The fish were fed every other day, the feeds being applied at the following metabolic weight rations: 0.6% administered in one portion and 1.2% administered in two portions at about 6 h intervals. The fish were fed either of the two commercial extruded feeds (Dan-ex 2545 and Aller 37/12) or a commercial pelleted feed (Cargill 2806). The Aller 37/12 and Dan-ex 2545 feeds, applied at 0.6% metabolic weight, proved most advantageous in terms of food conversion ratio (FCR), total weight gain (TG), and feed consumption per kg fish (FC), while the best values of haematological indices (RBC, WBC, Hb, MCH, MCHC, MCV) were recorded in the fish fed Dan-ex 2545 at 0.6% metabolic weight ration.

Blood parameters of 325.60±27.54 to 532.00±42.40 g mean individual weight carp kept in heated water cage culture at different feeding regimes (DAN-Ex 2545 and Aller Aqua Carp Grow feeds applied in seven treatments) were studied during 3-4 November 1999. Effects of the treatments on fish weight, erythrocyte count, and erythrocyte extension index were determined.