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 Mi(,dzyodrze, a deltaic area situated in the vicinity of Szczecin.
Il,;fTRODUCTIONAlong with the roach, the common bream is the most important fish species in freshwater areas of Poland. Biology of bream inhabiting Polish waters is relatively well known. The ample list of relevant publications includes papers by Filuk (1957Filuk ( , 1963 Bream has always played an important role in fisheries of the downstream section of the River Odra and its estuary (Neubaur 1926;Zimdars 1941; P�czalska 1963 b; P�czalska and Kraczkiewicz 1972;Kompowski and Pienkowski 1992). The species is very common in the Mi�dzyodrze waters as well. Mi�dzyodrze is a deltaic area in the lower part of the Odra, situated upstream of Szczecin and consisting of two major river branches: the Re galica and the Western Odra, interconnected by a complex system of minor branches and canals. Most of the Mi�dzyodrze area is a bream habitat, hence it is understandable that the
Changes in the Lake Diibie ruff gonad maturity and egg diameter were studied. Absolute.and relative fecundity values were calculated. The egg diameter distribution suggests portional spawning. The absolute fecundity was found to range within 13,338-82,233 and was most closely correlated with the total fish weight. No effect of body size, age, and ovary weight on the relative fecundity was found.
Background. This study aimed to determine survival rate, extent of cannibalism, and growth rate of northern pike (Esox lucius L.) larvae fed live zooplankton during a grow-out period, i.e., the time prior to when fish become valuable as stocking material. An attempt was also made to assess the food conversion ratio (FCR) with respect to the natural food applied. Materials and Methods. Grow-out operations began with 1-day-old pike larvae and involved experimental in-ground tanks with no artificial aeration, forced water flow, artificial circadian lighting, or temperature control. Differently structured habitats (black polyethylene foil, vascular plants, or plastic netting) were placed in all the tanks to separate larvae and provide cover. Feeding live zooplankton to the larvae began on day 3 and food was administered such that larvae were always surrounded by a zooplankton "cloud." Results. The survival rate during the first-(days 1-7) and second (days 8-27) stage of culture was 92.3% and 95.7%, respectively. Highest survival rates were associated with tanks with polyethylene foil habitats, while lowest survival rates were associated with tanks containing plastic netting. No cannibalism was observed in any tank. During the growout period, the total length of larvae increased by an average of 20.88 mm. Although the length increase observed in the three experimental treatments was similar; the significantly highest (P < 0.01) mean length (32.66 mm) was associated with larvae raised in tanks containing polyethylene foil. Until day 13, the mean weight of the larvae did not differ between the three treatments (P = 0.21). At and beyond day 20, fish kept in tanks equipped with polyethylene foil exhibited higher weight increments and on termination of the experiment the mean individual weight of larvae was significantly higher (P < 0.05) than those of larvae in tanks with vascular plants and plastic netting. The food conversion ratio, calculated for the entire culture period was 4.9. Conclusion. High survival rate of the cultured pike larvae demonstrated the success of pike larvae grow-out under uncontrolled conditions.
Academy of Agriculture The otoliths back readings method was applied to test the growth rate of Gymnocephalus cemuus from the three water basins of the Odra estuary area. Usability of the von Bertalanffy's equation and quadratic and cubic polynomials theoretical reading of length and weight growth rate was compared. The weight growth of fish aged two to eight was stated to be very uniform.
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