The study was aimed at determining effects of catastrophic floods of 1997 and 2001 on survival and growth rate of parr (0⁺ and 1⁺) of the brown trout in two tributaries of the Kamienica Nawojowska (the River Dunajec system, southern Poland). The survival rate of parr was studied, after stocking in the rocky-bed stream of Homrzyska, was lower than that of the fry stocked into the stream of Kamionka, characterised by alluvial bed. The passage of flood waves in 1997 and 2001 in the Kamionka resulted in a more than 15- and a more than 10-fold reduction in the survival rates of the 0⁺ and 1⁺ parr respectively, compared to survival levels observed in years without catastrophic floods (1998–2000). None of the brown trout parr stocked in the Homrzyska survived the catastrophic floods. The growth rate of the 0⁺ and 1⁺ parr was, in the flood years, half and one-third of the rates recorded in the years without catastrophic floods, respectively.

The study was aimed at comparing mortality and growth rate of the brown trout fry released, in autumn 2001 and spring 2002, to three tributaries of River Kamienica Nawojowska (the River Dunajec system in southern Poland). The released fish were tagged by adipose fin clipping and Alcian Blue injection. The recapture operations were conducted on 1 March and 2 September 2002. The fry released in autumn showed a higher daily instantaneous mortality rate than that found in the brown trout released in spring. The daily instantaneous growth rate was distinctly lower in the fish released in autumn than in those stocked in spring. The daily instantaneous mortality and growth rates were significantly dependent on the fry size.

The length growth was estimated, using the Dahl-Lea back-calculation method, in the vendace inhabiting two vendace-type lakes (Łańskie and Pluszne), similar in surface area (about 1000 hectares) and depth (more than 50 m), which, for many years, have been showing extensive fluctuations in vendace catches. The total length (LT.) of the vendace caught in the Pluszne was lower by more than 2 cm, on the average, compared to the total length of the vendace caught in Lake Łańskie, although gill nets of identical mesh sizes were used in both lakes. Analysis of length increments showed the Łańskie vendace to have grown at a faster rate. As from the second year of life on, the differences between mean lengths were very highly significant (Student’s t test, α<0.001). As demonstrated by comparing vendace growth between the early 21st century (samples collected during the 2003 spawning season and March 2004; in the case of Lake Pluszne, a sample obtained in July 2005 was included into the analysis) and the 1960s and 1980s, the present (early 21st century) growth rate in the Pluszne is slower than it used to be. In contrast, the vendace growth rate in the Łańskie has not changed. The Pluszne vendace grow rate shows a pattern similar to that reported from the vendace of Lake Narie, known in past decades for its slow growth. Most probably, the unfavourable conditions of life the Pluszne offers the older vendace at present (the fish stay mainly in the epilimnion during the summer), manifested as intensified competition for food, result in periodic food deficiencies and retard the individual growth rate.

The average growth of bream body length, average annual body length, and body weight gains were determined by taking appropriate measurements and weighing the fish. The study involved bream individuals collected from the Solina (447 fishes), Tresna (190), and Rożnów (804) dam reservoirs. The fish age in the reservoirs sampled ranged within 4–15, 3–13, and 3–10 years, respectively. The Rożnów bream was distinct in their highest growth rate, followed by the fish collected in the Tresna and in the Solina. The 10-yr-old bream in the Solina, Tresna, and Rożnów were characterised by the average body length 30.8, 31.9, and 41.5 cm, respectively. The high growth rate of the Rożnów bream was probably a result of, i.a., repeated net fishing operations in the past, such operations being recommended as a basic measure in the management of fishing and angling in all dam reservoirs.

Growth of age group 0 (young-of-the-year) of four year classes of the Międzyodrze roach was followed. The mean daily increments of modal length of the 1996 and 1997 year classes differed by a factor of 2. The year classes of 2000 and 2001 grew in the first part of the growth season (May–June) several times faster than in the later part (July–August). Winter length increments in the 1996 year class were negligible. The theoretical length at which scales appeared was estimated at 12.48 mm or 19.39 mm (SL), depending on the method applied. Using back calculations, the mean length at the first annual ring appearance (L₁) was estimated at 44.88 ± 5.54 mm (SL).

The studies of Lake Będgoszcz and the adjoining waters (of the rivers: Krzekna, Ostrawica and the Nieborowski Canal – the River Bielica) were conducted in the years 1996–2001. Lake Będgoszcz was fund to be a polimictic body. Oxygen conditions in the lake waters were similar during the entire study period. The surface waters were usually better oxygenated, though. Clearly, the vertical distribution of oxygen occurred in the summer. The least favourable oxygen conditions occurred in the autumn, and the minimal amount of dissolved oxygen occurred in the bottom waters (4.8 mgO₂·dm^-3). The organic matter and chlorophyll ”a” contents in the waters of Lake Będgoszcz proved considerable trophy of these waters. The biggest concentration of total nitrogen was found in the surface layer in the summer (mean 2.69; maximum 4.81 mgN·dm^-3), whereas, its lowest value in the same layer was recorded in the winter (mean 1.96 mgN·dm^-3). The biggest concentrations of total phosphorus were observed in the surface layer in the spring (0.52 mg·dm^-3), whereas, the lowest value in this layer was recorded in the autumn (0.19 mg·m^-3). The conducted investigations proved that Lake Będgoszcz was hardly resistant to degradation and its drainage basin easily activated loads of the biogenic matter deposited in its area. This water body has been subject to intense eutrophication. It shows hypertrophic characteristics. Lake Będgoszcz is under the threat of nitrogen coming from farming sources. The waters in the studied lake stay outside classification according to the guidelines of the basic lake monitoring system. Habitat conditions prevailing in the lake during the study period did not pose any threat to ichthyofauna. Therefore, the lake may be classified as a pike-perch lake according to fishing typology.

The paper proposes an index that adds to characterisation of length growth in various fish species. The index, mean length increment ratio, describes the shape of the growth curve. The analyses included 799 samples (about ten to several hundred individuals in each sample) of 20 fish species. The mean increment ratios were determined in four methodological variants (A, B, C, and k); detailed statistical analysis, however, has revealed that the A variant, calculated using the full age range of the material, is the most authoritative one. The values of A ranged from 0.60 (herring) to 1.02 (wels). The mean A for 20 studied fishes was 0.89. The A value was found to be significantly correlated with age (for 17 out of 20 analysed fishes). Cluster analysis (performed for A and k) demonstrated that 3 species (herring, vendace, and whiting) were considerably distant from the remaining 17 species; those 3 fishes exhibited a sharp decrease in growth rate, which in the other species was more even.

The study was aimed at comparing effects of rearing whitefish larvae on three types of diets, i.e., a trout starter, frozen zooplankton, and a mixed diet (starter + frozen zooplankton). After 21 days in culture, fish survival rate and growth were similar in the three treatments (P>0.05). All the three diets can be successfully applied in rearing whitefish larvae. When an artificial feed is used, it is advantageous to supply the diet with natural food for the first two weeks of culture. The mixed diet consisting of the artificial feed and frozen zooplankton resulted in a four-fold reduction of the risk of abnormal swimming behaviour (swimming on the side) observed on a mass scale in the larvae fed exclusively the artificial feed.

The study focused on zooseston of the River Drawa, sampled downstream of the river’s outflow from Lake Grażyna (Site I), and that of a forest stream downstream of its outflow from Lake Krzywy Róg (Site II). The number of taxa at Site II was almost twice as high as that at Site I. The zooseston of the two sites shared as few as 24 taxa. The zooseston density at Site II was, on the average, almost 50 times higher than that at Site I, the biomass being 9 times that of Site I. Most abundant among crustaceans at Site I were Bosmina longirostris and nauplii, Polyarthra sp. being the most abundant rotifer. At Site II, the most abundant taxa included B. longirostris, Chydorus sphaericus, and nauplii as well as Keratella cochlearis and P. vulgaris. The highest biomass contributors at Site I were nematodes and chironomid larvae, B. longirostris, copepodids, and Asplanchna sp., the highest contributions to biomass at Site II being those of Polyarthra sp., K. cochlearis, Ascomorpha ecaudis, and Ch. sphaericus. Throughout the year, Site I witnessed the passage of 44 575 kg of zooseston, a quarter of that amount having passed Site II. Those amounts, when used as food, would be sufficient to support 8915 and 2165 kg non-predacious fish at Site I and II, respectively, i.e., equivalents of 4 457 510 and 1 082 520 fish fry individuals of 2 g individual weight.

Age 1+ vimba fry tagged with visible implant fluorescent elastomers (VIFE) were introduced into the water bodies of the Drawa National Park in 2003, within the framework of a vimba restitution program. VIFE, applied for the first time to mark the vimba, have been widely used for marking not only fish, but also other vertebrate groups (amphibians and reptiles), as well as the invertebrates. The advantages of this method include simplicity, easy identification of tagged animals, high retention rates of the tags and a minimal effect on the survival rate, growth rate and behavior of animals.

Experiments were conducted to determine the effects of pH on ammonia and their combined effects on the stress response of steelhead trout, Oncorhynchus mykiss. Stress levels were studied by monitoring both primary and secondary stress responses. It was found that fish subjected to higher levels of pH and ammonia exhibited increased levels of stress. This was demonstrated through primary physiological stress response, plasma cortisol, and secondary physiological stress response, plasma glucose and blood hematocrit. It was concluded that careful regulation of pH and ammonia in the recirculating aquaculture system could relieve excessive stress allowing the fish for better survival and growth.