In the present paper results of the analysis of metric and meristic features of flounder from the Słupsk Furrow are demonstrated. Moreover, the material collected allowed to show the length and age distribution of the flounder, as well as the growth rate of length and weight was estimated. All examinations were performed with regard to both sexes. Results obtained were compared to data of the flounder collected in the Pomeranian Bay area.

Peled larvae (Coregonus peled Gmel.) were reared in illuminated cages in two stocking densities (10 000 and 40 000 fish per cage) from the end of April to the end of June. Partitioning of food resources by larvae was determined among size classes with reference to the number and energetic value of consumed zooplankton prey. After hatching all larvae had nearly the same body size. With the growth a notable differentiation in their size followed. It was the result of unequal distribution of food among fish, especially in the case of energetic value of consumed organisms. Usually, regardless of the number of prey consumed, peled larvae that were the smallest on the following days, shared the smallest part of zooplankton energetic value, the larvae of the largest size had the biggest part. The smallest larvae attained maximally up to 53.5% of average energetic value of consumed food, the biggest fish exploited even up to 365.6%. Such unequal food intake at early life stages determines the animal individual rank in social hierarchy, and is frequently considered as a control mechanism in population dynamics.

The study was carried out in a grass carp cage culture located in thermal effluent canal at the Fisheries Research Station of the Department of Aquaculture, Agricultural University of Szczecin, within 18 June – 6 September 2002. The study involved fry of the grass carp aged 1+ and mean individual weight of 135 g (±15g), stocked at a density of 30 individuals per cage (10 individuals m^-3 water). The experiment was aimed at determining possibilities for growing out the grass carp in cooling water, on a diet consisting exclusively of water hyacinth, and at comparing growth rate and efficiency of food utilisation in the fish kept on a mixed feeding schedule (commercial feed + water hyacinth). In Treatment A, the fish were fed the commercial feed (Aller Master) only; Treatment B involved a mixed feeding of 3 days on the Aller Master and 1 day on water hyacinth; water hyacinth only was fed in Treatment C. All the fish in all the cages were weighed at 8-day intervals to adjust food rations and to calculate the food conversion ratio (FCR). Chemical analyses of the fish body, performed on termination of the experiment, allowed to calculate the apparent net protein utilisation (aNPU), energy retained (ER), and apparent lipid retained (aLR). The values obtained revealed water hyacinth to be ineffective food for the grass carp of the size used in the experiment. This was demonstrated by exceptionally high FCR values and very low body weight gains (6.4%). Increasing contribution of water hyacinth in the diet was accompanied by reduction in the body lipid content. The body weight growth of the fish fed the commercial feed was decidedly higher than that of the grass carp fed exclusively water hyacinths. The commercial feed offered at a 2% metabolic weight ration allowed to obtain a satisfactory growth rate at a cost-effective feed utilisation.

This paper presents the sexual cycle occurring in the artificially bred rudd (Scardinius erythrophthalmus). In females, endogenic vitellogenesis took place between autumn and spring and the exogenic vitellogenesis was observed in May. At the end of May and at the beginning of both June and July, synchronised and unsynchronised oocyte development was observed in the females. Oocytes with a complete exogenic vitellogenesis and previtellogenic oocytes were found in the synchronised development. Besides the two above oocyte stages, oocytes in the vacuolisation stage were found in the unsynchronised development. The male testicles contained spermatocytes from July to April. Spermatids were observed in May and June. At the beginning of July, new spermatocyte generations were formed. The obtained results indicate that the rudd is a species with a spring exogenic vitellogenesis and that both synchronised and unsynchronised oocyte development can occur in the period preceding reproduction.

Vertical distribution of benthic macrofauna in sandy sediments of the Pomeranian Bay (southern Baltic) was analysed from a total of 99 samples collected from 10 sites visited four times within 1996-1997. The sediment, collected with a box corer, was divided into 5-cm thick layers. The sediment deeper than 5 cm was found to support about 28% of the total macrofauna biomass; the bulk of the macrobenthic biomass there being due to large individuals of Hediste diversicolor, Marenzelleria viridis, Mya arenaria, and Macoma balthica. The macrofaunal biomass within the depth layer of 5-10 cm is dominated by M. arenaria, polychaetes predominating deeper than 10 cm in the sediment. Most of the sandy bottom macrofauna is accumulated within the top 10 cm of the sediment. The exception is the polychaete Marenzelleria viridis, capable of occurring much deeper. Some individuals of various epifaunal and surficial infaunal species were encountered deep in the sediment; most probably, they found their way there due to burrows dug by large infauna. A relatively accurate estimate of abundance and biomass of the macrobenthos of the sandy bottoms of the Pomeranian Bay can be obtained only when and if the benthos is sampled by a gear that penetrates the sediment down to at least 10 cm.

Data on the abundance and biomass of benthic macrofauna off the River Świna discharge to the Pomeranian Bay (southern Baltic), obtained as a result of a single sampling event, were subjected to a multivariate analysis involving ordination by means of multidimensional scaling (MDS). The analysis identified two groupings: west and east to the shipping channel bisecting the area of study. The dissimilarity matrix-based analysis of variance (ANOSIM) showed significant differences in abundance and biomass between the two groupings. The separation was mainly a product of differences between the abundance and biomass of oligochaetes, Hediste diversicolor, Marenzelleria viridis, Streblospio shrubsoli, Manayunkia aestuarina, Mya arenaria and Macoma balthica, higher west of the channel as well as the lower abundance and biomass of Pygospio elegans, Cyathura carinata, Mytilus edulis, and Cerastoderma lamarcki. The major underlying cause of the differences between the two parts of the area is the organic enrichment of the sediment west of the channel. The macrofauna biomass there was five times that recorded east of the channel.

During a 1-day cruise in June 1995, samples of water and bottom sediments were collected east and west of the shipping channel off the River Świna discharge site into the Pomeranian Bay. Water temperature, and dissolved oxygen content were measured in the near-bottom layer; salinity and contents of suspended particulates and chloroplastic pigments (chlorophyll a and phaeopigments) were determined near the water surface and in the near-bottom layer. In addition, sediment granulometry, organic matter content, and chloroplastic pigments were analysed separately in the uppermost 1 cm and deeper in the sediment. Non-parametric statistical test was applied to evaluate concordance in changes of sediment characteristics in the entire area of study. Near-bottom water and sediment characteristics on both sides of the shipping channel showed a number of differences. The differences in water parameters analysed resulted from instantaneous changes in structural characteristics of the water column at the moment of sampling, while differences in sediment characteristics are persistent. West of the shipping channel, the bottom sediment is dominated by very fine sand fraction; the contents of silt/clay, organic matter, and chloroplastic pigments are higher there than east of the channel. The sediment chlorophyll a content is indicative of a higher input of fresh plant material from the water surface and its enhanced retention west of the channel.

The paper describes hydrochemical conditions and trophic status of lakes Mętno and Ostrów, the largest water bodies in the Cedyński Landscape Park. The study was conducted in 1998-2000. The lakes were found to differ in their water mass dynamics: Lake Mętno was polymictic, water dynamics of Lake Ostrów placed it near bradymictic. The oxygen regime of near-surface and near-bottom layers, nutrient contents and Secchi disc visibility are indicative of considerable fertility of the lakes studied. The Mętno should be classified as strongly eutrophic. Spatial and tempral changes of mineral forms of nitrogen were typical of eutrophic reservoirs showing a clear trend towards deposition of nitrogen in bottom sediment. The eutrophic nature of the lakes studies is confirmed also by the high concentrations of phosphorus compounds. All the mineralisations indices evidenced an averege mineralisation level, typical of the Western Pomeranian surface waters. The scheme of anion dominations was following: HCO₃^- + CO₃^2- > SO₄^2- > Cl^-.

The experiment involved 275 (±20.0) g mean individual weight young carp, stocked in 2 m³ cages at a density of 6 individuals per cage. Over the 58 days of the experiment, the fish were fed an extruded feed of 45.5% crude protein, 24.2% total lipids, and 23.1 MJ·kg^-1 gross energy contents. The experimental treatments differed in the magnitude of daily feed ration, calculated relative to the fish metabolic weight (W^0.8). The carp receiving feed rations of 0.8, 1.8, 2.6, 3.2, and 3.6%W^0.8 showed specific growth rates (SGR) of 0.98, 1.91, 2.41, 2.49, and 2.51%·d^-1, respectively, the respective food conversion ratio (FCR) values being 0.97, 1.04, 1.14, 1.37, and 1.52. The highest apparent lipid retention (aLR= 76.27 %) and the highest amount of energy retained (ER= 46.96%) were recorded in the carp fed the 2.6W0.8 feed ration, the highest apparent net protein utilisation (aNPU= 40.14%) being observed in the fish fed the lowest feed ration. The results demonstrate energy-rich feeds to have a potential for successful application in intensive culture of the C_2-3 carp kept in cooling water.