The vendace individuals examined showed the following characteristics: D III 8-10; A III 9-14; V II 9-11; P 3-15; sp.br. 1 40-46; r. branch. 7; l.l. 72-81. The Leśne vendace differed from other populations described in the literature in having a higher dorsal fin (X19) only. A comparative analysis of the vendace caught in the Leśne in autumn and spring showed a number of differences in morphometric characters, the differences resulting mainly from the fact that those individuals caught in spring had their ventral parts filled with gonads.

In the experiment, fertilized eggs of grass carp Ctenopharyngodon idella Val. were exposed to copper (0.3 mg·dm-3) or lead (4.0 or 5.0 mg·dm-3) at 20, 24, 25, 28 or 30°C. Newly hatched larvae were counted and inspected. Body malformations of the larvae were examined. The proportion of deformed larvae was determined and the malformations were identified. The deformed larvae were described in detail and their images recorded with the MultiScan computer image analysis system. The highest hatching success rate was observed in the control fish kept at 24-25°C. Although malformations were observed among them, they were rare. The most common malformations were single vertebral abnormalities. Incubation at the temperatures below and above the optimum range resulted in a reduced hatching success rate and an increased frequency of body malformations (even to 100%). Exposure to the heavy metals, too, considerably reduced the hatching success rate and increased the frequency of body malformations. These included various vertebral curvatures, yolk sac deformations, and shortening of the body. The malformations observed in the grass carp larvae were very similar to those reported earlier from the common carp.

Differentiation of the alimentary tract during larval development of asp (Aspius aspius L.) was followed using histological techniques. At hatching, the mouth cavity, pharynx, and oesophagus of the larvae were occluded. The intestine, in the form of a straight tube with undifferentiated cells, was resting on the yolk sac. Between days 3 and 5 post hatch, the intestine opened at both ends and lined with columnar epithelium. Signs of digestion and lipid absorption by enterocytes were observed on day 5, while protein absorption started on day 7 of the larval development. Goblet cells that produce acid mucins were detected among differentiating cells of the mouth cavity on the day of hatching. Intestinal mucous cells appeared on day 5 and began secreting neutral and acid mucins. The yolk sac was completely resorbed on day 11 post hatch. On day 21, the larvae measured, on the average, 17.23 mm in total length.

The experiment involved three ranges of water temperature: 11-13; 15-16; and 18-20°C, applied during incubation of eggs produced by pond-reared ide spawners. Each temperature range was maintained in 5 tanks, each holding 100 fertilised eggs the survival rate of which was being assessed. Throughout the experiment, the incubated eggs were examined and the timing of the onset and termination of hatching was determined. Once the larvae hatched, their total length as well as the length, height, and volume of the yolk sac were measured. The highest egg surival rate (64.6%) occurred at the lowest incubation temperature range (11-13°C), a somewhat lower survival (59.2%) being recorded at 15-16°C. The lowest survival rate (about 40.6%) was typical of the highest incubation temperature range. The duration of egg incubation and embryonic development of the ide was found to be related to water temperature. The 11-13°C range delayed the onset of hatching and prolonged its duration. Incubation at 18-20°C was found to accelerate the embryonic development and was decisive for the earliest onset of hatching and its shortest duration. The longest larvae (6.25 mm total length) were those hatched from eggs incubated at 15-16°C. Those larvae hatched from eggs incubated at 11-13°C were shorter (averaging 6.06 mm total body length). The smallest larvae (5.81 mm total body length) were those hatched from eggs incubated at 18-20°C. The size of the yolk sac in the newly hatched larvae was dependent on water temperature prevailing during the embryonic development. Yolk sacs of the larvae hatched from eggs incubated at 11-13 and 15-16°C were larger than those of the larvae hatched from eggs incubated at the highest temperature range (18-20°C).

The paper describes results of studies on adaptation of the principle of Chinese fish polyculture, dominated by grass carp fed green forage, to Polish conditions. Over the course of the experiment, fish yield increments obtained averaged 1,444; 960; 1,374; and 1,498 kg ha-1 in the four successive years. The data demonstrate that a modified polyculture allows to arrive at relatively high fish yields without the need to use expensive feeds and substantial labour input.

The study involved a total of 633 pikeperch individuals caught within 1995-2000 in Lake Dąbie, the Szczecin Lagoon, and the Pomeranian Bay. The length and weight growth as well as the condition of the fish were analysed with commonly used methods. The verge coefficient (Kr) and the verge increment (Pk) were determined for each individual. The Kr value was subsequently taken into account to ascribe each individual to an appropriate age groups; when Kr > 0.5, the age assumed from the number of annual rings was augmented by 1. The results showed the length growth to be rather similar (particularly in the earlier phase of life) in different samples. On the other hand, the Lake Dąbie pikeperch revealed a clearly slower growth rate and a poorer condition. Noteworthy were the dynamics of Kr and Pk over a year: the highest values were recorded in winter, the lowest being typical of summer. Changes in Kr allow to contend that the annual ring on a pikeperch scale is usually formed during summer months.

The study involved 3 predacious fish species from Lake Miedwie: zander (22 individuals examined), pike (85), and perch (316). The food composition, feeding intensity, food diversity, and size relationships between the predators and their prey were studied. The food of the predators studied consisted almost exclusively of fish; it was only the perch food that contained also the American crayfish (Orconectes limosus) and culicid pupae. The food was dominated by smelt, roach, perch, and unidentified fish. The largest fish were consumed by pike, the smallest being eaten by perch. The prey of the maximum and minimum relative length (as expressed in per cent predator length) were consumed by perch and zander, respectively.

The crustacean Daphnia magna was cultivated, over two culture cycles, during the growing season of 1996. The cultures were kept under natural conditions of temperature and photoperiod, without any technical installations. The cladocerans were fed a fish processing plant wastewater in which an intense chlorophyte bloom was induced. The bloom was triggered in the raw wastewater by inoculating it with the chlorophytes Scenedesmus sp., Chlorella sp., or a mixture of the two. The D. magna population growth was controlled by harvesting it with different intensities. The highest yields (71.644 mg wet weight, i.e., 671.92 mg·dm-3 in summer and 180.694 mg, i.e., 1778.58 mg·dm-3 in autumn) were obtained from those populations subject to the most intensive exploitation. Productivity of a population was correlated with harvest intensity. Yields from the 51- and 70-d-long cycles were 2.2 and 2.7 times higher, respectively, than the yield from an on-exploited D. magna population. Compared to the latter, the harvested populations showed a higher reproductive rate.

Age and growth rate of 99 rudd individuals caught in September 1993 with a fishing rod in the River San backwater near Hurko were determined. Growth rate was estimated with the back calculation technique utilising the linear relationship between the caudal scale radius and body length. Growth rate of the rudd was described with the equation: l.c.(t) = 30.0(1-e-0.0737(t+1.9)) Compared to data from other areas of Poland, the rudd studied showed a very fast growth rate in the first year of life, the growth becoming very slow thereafter.