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The aim of the experiment was to identify the possibilities of stimulating pikeperch spawning with human chorionic gonadotropin (hCG) and Ovopel, a mammalian GnRH analogue (D-Ala⁶ Pro⁹ NEt-mGnRH) with a dopamine inhibitor (metoclopramide). Pikeperch spawners were caught with trap gear (fyke-nets) during the pre-spawning season from the Tałty and Tałtowisko lakes (Masurian Lakeland, northern Poland). After transport that lasted an hour, the fish were placed in tanks in a recirculating system and then segregated by sex. The females were divided into five experimental groups, each containing six specimens. The fish were injected twice at 24 hour intervals with hCG (group I - 200 and 200IU kg⁻¹ body weight (BW); group II - 200 and 500IU kg⁻¹ BW), Ovopel (group III - 0.25 and 0.50 pellets kg⁻¹ BW; group IV - 0.25 and 1.0 pellets kg⁻¹ BW) or 0.7% NaCl solution (group V, control - 0.2 and 0.5 cm³ kg⁻¹ BW). The effects of the hormonal stimulation expressed as the percentage of ovulating females, the degree of spawning synchronicity, and survival of the embryos to the eyed-egg stage were highly differentiated. The highest percentages of spent fish were obtained in the group stimulated with hCG - 83.3% (group I) and 100% (group II) of the females ovulated. The development of the oocytes in this group was rapid and synchronous, which was reflected in the shortened and relatively similar latency period (47 - 57 hours following the first injection; mean ≈ 51 hours) in individual females. No impact was noted with regard to hCG dose (400 vs. 700 IU kg⁻¹ BW) on the latency time or on egg quality. Ovopel did not positively affect either oocyte maturation or pikeperch ovulation. None of the fish from group III ovulated, and in group IV, as in the control group, eggs were obtained only from three (50%) females. In contrast to group V, the eggs of females stimulated with Ovopel were of low biological quality and survival to the eyed-egg stage ranged from 0 to 8%. Higher mortality among the females was also noted, especially in group III. The experiment indicated that hormonal stimulation with hCG is effective, while that with Ovopel was surprisingly ineffective.
The aim of the study was to determine the oxygen consumption (OC, mg O₂ kg⁻¹h⁻¹) and ammonia production (AE, mg TAN kg⁻¹h⁻¹) of perch reared in a recirculating system at the optimal temperature for this species of 23°C. The studies were conducted when the fish were undergoing intense fattening on artificial feed. Measurements of metabolic rate were taken 24 hours per day in six size groups of fish (mean body weights (BW) in each group - 18.4, 30.7, 46.4, 56.5, 67.8, 82.3 g). Within the studied perch size range, OC decreased from 336.2 to 185.0 mg O₂ kg⁻¹h⁻¹, and AE from 22.0 to 5.6 mg TAN kg⁻¹h⁻¹. An increase in body weight by 1 g led to an average decrease in oxygen consumption by a mean of 2.53 mg O₂ kg⁻¹h⁻¹ and ammonia excretion by 0.28 mg TAN kg⁻¹ h⁻¹. During the analyzed period, the body weight of perch, the arithmetic dependence between OC-BW and AE-BW, was linear and the determination coefficients R² of the linear regression equations describing these relationships were highly statistically significant at a value exceeding 0.9.
The aim of the study was to determine the impact of feeding frequency (one, two or three feeds and continuous feeding) on the magnitude of oxygen consumption (OC, mg O₂ kg ⁻¹ h ⁻¹) and ammonia excretion (AE, mg TAN kg ⁻¹ h ⁻¹) by juvenile perch. The study was conducted during routine rearing in a recirculating system. No significant impact of the applied feeding schedules (P > 0.05) on the average diurnal values of OC and AE was confirmed. The values ranged from 165.88 mg O₂kg ⁻¹ h ⁻¹ (one feed) to 188.48mgO₂ kg ⁻¹ h ⁻¹ (continuous feeding) and from5.51 mgTAN kg ⁻¹ h ⁻¹ (two feeds) to 6.44 mg TAN kg ⁻¹ h ⁻¹ (continuous feeding). The feeding schedule had a significant influence on the diurnal fluctuations of oxygen consumption and ammonia excretion and was especially evident in the latter. The AEmax/AEaverage ratio in the group of fish fed once was 2.46, but the AEmax/AEmin ratio was 19.01. AE variability over a twenty- four hour cycle was much lower in other feeding schedules.The course of the diurnal profiles of OC and AE was characteristic for each of the applied experiment variants. Statistically significant dependencies were confirmed between ammonia excretion and oxygen consumption (P<0.001) and were specific to each experiment group. Correlation coefficients of the linear regression equation that describes the AE - OC relation ranged from 0.57 (three feeds) to 0.94 (two feeds). The values of OFR (kg O₂ kg ⁻¹ feed fed day ⁻¹) and AFR (kg TAN kg ⁻¹ feed fed day ⁻¹) were not determined by the applied feeding schedule (P > 0.05).
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