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Length and weight growth rates of 206 bream individuals caught in 1992 and 1995 were back-calculated. Different types (non-linear vs. linear) of a relationship between the scale caudal radius and body length were revealed to prevail in the two years. The 1992 bream grew very rapidly during the first four years of life, the growth rate slowing down later on. On the other hand, the bream growth in 1995 was more uniform over time. No sex- or age-dependent differences in growth rate were found. The Lake Dšbie bream population belongs to the fast growing populations of the species.
Growth rate (based on fry length measurements and back calculations), condition, relative gonad size, and length at first maturity were determined in the common bream population inhabiting Międzyodrze, a deltaic area situated in the vicinity of Szczecin.
Location of the monogenean Diplozoon paradoxum on the branchial arches of the Vistula Lagoon bream is described. The highest number of parasites was found on the first gill arch, followed by the numbers recorded on the second and third arches; the lowest numbers of the monogenean were typical of the fourth arch. About 70% of the monogeneas were found to dwell on the dorsal part of the branchial arch. It is concluded that the distribution of parasites is controlled by the direction of water flow through the gills as well as the size of the gill arch occupied by the helminths.
Within 1997-1999, studies were carried out in Włocławek Reservoir to determine diet composition, growth rate, and condition of common bream, Abramis brama (L.)-the dominant fish species there. An extraordinary abundance of bottom fauna in this reservoir is the reason that already in the first year, common bream begin to feed intensively on zoobenthos, they grow very rapidly (in length and weight), and are in good condition. Literature reports that at the beginning of the 1980s, when zoobenthos in the reservoir was considerably less abundant, bream growth was slower.
Physiological parameters in fish provide grounds for conclusions as to the physiological status of the organism. The status is directly related to inner and outer factors, biotic and abiotic influences which act on the organism. Present studies aimed at defining the set of immunological and haematological indices in breams, which form fish populations in Dabie Lake and Szczecin Bay, whose ecosystems differ in water cleanness. Immunological studies in breams involved determining selective defensive functions of neutrophilic granulocytes, expressed by the index of phagocytosis of a standard bacterial strain (Ipg), the percentage of phagocytes which ingested the bacteria (%gp), NBT index, the amount of formazan and the index of myeloperoxidase activity (WA MPO). Haematological studies included determination of absolute leukocyte number and the differential leukocyte pattern. Bacteriological and physicochemical studies were also performed on water samples of reservoir sites from which the fish originated. Results of examination of water samples from Dabie Lake and Szczecin Bay demonstrated a significant level of water pollution in the ecosystems. A definitely higher level of water pollution, particularly in respect to bacterial contamination, was observed in Dabie Lake. Comparison of immunological and haematological results demonstrated significant differences between the two studied bream populations, i.e. those originating from Dabie Lake and the other, originating from Szczecin Bay. Such differences were disclosed both in immunological and in haematological indices.
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