Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 32

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
Age and growth rate of asp (Aspius aspius) from the Pierzchały Reservoir were estimated by back calculations based on scale readings (annual rings identification). The scale reading procedure was complicated by presence of additional rings, called "juvenile" (these appearing within the first year′s increment) and "spawning" (present on scales taken from individuals older than 3 years). These additional structures were not characteristic for all the examined individuals. Localisation of the first annual ring was complicated by fairly fast growth rate during winter, so the typical zones of narrow sclerites, indicating slow-growth season did not occur, affecting the scale readability. The quantitative share of asp in control catches amounted to 9%. Most of these individuals (70%) were to 4 to 7 years old. The oldest asps were aged 12, at body length of 66 cm and body weight of 4500 g. The Pierzchały Reservoir is merely exploited by fishermen.
The fecundity of a local, stationary population of vimba bream Vimba vimba (L.) from Lake Ostrowieckie (Oder River drainage area, northwest Poland) was analyzed. The number of eggs in the ovaries was determined by the weight method. The individual absolute fecundity of vimba bream ranged from 9,560 to 157,000 eggs for females measuring from 19.2 to 34.0 cm and weighing from 121 to 693 g. Fecundity varied in the designated size classes from 21 thousand eggs for individuals below 22.0 cm to 104 thousand eggs for the largest ones (longer than 30.1 cm). The average fecundity in the youngest group of females (4+) was 25.6 thousand eggs, while that in the oldest group (9+) was 120.1 thousand eggs. Correlation analysis of absolute fish fecundity versus selected biometric parameters showed a significant dependence.
The aim of the study was to determine the food preferences of the black cormorant and to assess fisheries losses in Włocławski Reservoir. Twenty fish species were identified in the cormorant diet. The dominant species were ruff and perch (29.4% and 24.4 % of the weight share, respectively). Roach (11.9%) and Prussian carp (10.9%) were also important components of the cormorant diet. The share of invasive species from Gobiidae family was negligible (0.2%). Among the fish species important to commercial and recreational fisheries management, the most numerous in the cormorant diet were: ide (10 t; 2.7% of the weight share), pikeperch (8.6 t; 2.3%), asp (6.3 t; 1.79%), and pike (4.9 t; 1.3%). The fish biomass consumed by cormorants was a mean of 372.8 t annually, which is 46.6 kg per ha (range of 44.6 to 49.6 kg per ha). The analysis of fisheries losses in 2009 was estimated at 980,000 PLN.
Macroscopic and microscopic changes which occur during the annual ovarian cycle of vimba females from the Drawieński National Park (DNP) were studied. The study was carried out in 1997-1998 using 146 fish with an average body length (longitudo corporis) of 24.2 cm and an average body weight of 274.9 g.No abnormalities or pathological changes in the ovaries of the investigated fish were detected. The histological picture showed the clear asynchronicity of oocyte maturation. The following ovary maturity stages, characteristic for portion spawners, were distinguished: IV₂; V₂; IV₃; V₃. A relatively short post-spawning stage was also identified (VI/II). It was confirmed that in vimba from the Drawieński National Park (DNP) the longest the maturity stage is III, which starts in October and finishes in March or April of the next year.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 2 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.