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The aim of the experiment was to determine the impact adding a vitamin-mineral supplement to feed had on selected rearing indexes of juvenile common whitefish (Coregonus lavaretus) during rearing in a recirculating system. The study material comprised juvenile common whitefish aged 4 months with an initial body weight of 5.2 g and body length of 7.6 cm. During the experiment, the feed applied was extruded juvenile feed T - 1.5 Nutra MP Trouv (France). The experiment comprised two dietary treatments: group K (feed without a supplement) and group M (feed with a vitamin-mineral supplement). The feed supplement used was the MIK 1 mixture (Mikita, Lublin-Zemborzyce). The quantity added was 10% of the extruded feed. During the experiment, significant differences were noted in fish growth and the feed conversion coefficient (P < 0.05). Individuals with body deformities were noted during the experiment; the deformities manifested primarily as the shortening of the operculum and mouth anomalies. The number of these individuals differed in the two groups, and by the end of the experiment the number of individuals with body deformities in group K was significantly higher (13.8% of all fish) than in group M, in which such deformities were noted in just 1.3% of the fish (P < 0.01). Based on the results, it was concluded that through the application of the vitamin-mineral supplement higher biomass growth was attained, feed conversion was better, and the number of fish with body deformities was lower. Thanks to this, the rearing results of juvenile common whitefish in recirculating systems was more effective.
The aim of the experiment was to evaluate the growth and survival of larval Atlantic sturgeon fed microworms (Panagrellus sp.) and brine shrimp nauplii (Artemia sp.). The experiment was conducted at the Department of Sturgeon Breeding in Pieczarki of the Inland Fisheries Institute in Olsztyn. The experimental material comprised larval Atlantic sturgeon 22 days post hatch that were already feeding. The fish were stocked into nine tanks with a volume of 40 l each that were included in a recirculation system. The fish were divided into three experimental groups: group A was fed brine shrimp nauplii; group A+N was fed brine shrimp nauplii and microworms; group N was fed microworms. The fish from the group fed only brine shrimp nauplii attained the greatest body growth (0.068 g) and the highest survival (43.3%). Fish from group A+N, which received mixed feed, attained similar results for both growth and survival to that in group A (0.061 g and 33%). Differences between these two groups were not statistically significant (P > 0.05). The weakest results were obtained for the group fed only microworms. The fish from this group had a final body weight of 0.045 g and survival of 1.7%. The differences in these parameters among the groups were statistically significant (P < 0.05). The current experiment permits concluding that, at the moment, feeding microworms exclusively does not produce the anticipated results. Brine shrimp nauplii was a substantially better feed choice for larval Atlantic sturgeon. However, in both instances, further experiments must be performed before the precise daily ration or the manner in which the ration is divided over the day is determined. This information could improve the results of rearing substantially.
The aim of the study was to determine what impact feeding juvenile common whitefish, Coregonus lavaretus (L.), different feed rations had on rearing indexes and oxygen consumption during culture in recirculation systems. Three feeding treatments were applied: 2% (group L), 3% (group M), 4% (group H) of fish biomass. The final juvenile common whitefish weight increased with increasing daily feed rations. Fish from group H (largest feed ration) had statistically significantly (P < 0.05) higher body weights (50.3 g) and higher feed conversion ratios (1.14) than did the fish in the other two groups. However, the lowest oxygen consumption (192.9 mg O2 kg-1 h-1) was noted in group L (smallest feed ration). The results of the experiment indicated that the size of the daily feed ration has a significant impact on the rearing results and oxygen requirements of juvenile common whitefish. The optimum daily feed ration for juvenile whitefish weighing 10-45 g and at a water temperature of 18.0°C is 3% of the stocking density.
The aim of the study was to compare the effects of rearing juvenile pikeperch in two types of tanks used widely in hatcheries; the tanks had either round (group O) or square (group K) bottoms. Two experiments were conducted. In experiment I, the mean initial body weight (m.c.) of the fish was 0.33 g, and in experiment II it was 1.76 g. The factor studied (tank shape) had a significant impact on the fish growth rates and feed conversion ratio (FCR) and protein efficiency ratio (PER). The results obtained in the two experiments differed. With the smaller pikeperch (experiment I) better results were obtained in group O, while with the larger fish (experiment II) better results were obtained in group K. No differences among groups in fish condition or stock survival were noted. The results indicate that smaller juvenile pikeperch (m.c. ≥ 0.3 g) should be reared in round-bottomed tanks, while larger fish (m.c. ≥ 2g) should be reared in square-bottomed tanks. Using the appropriate tanks for rearing particular size groups of pikeperch could potentially result in increased growth and more effective feed conversion ratios, thus shortening rearing times and lowering production costs.
Larval pikeperch (Sander lucioperca L.) were reared at two initial stocking densities of 250 and 350 individuals per liter. The final body weight of the fish reared at the lower stocking density was 12.7% higher than that of the fish held at a higher density. The survival of the larvae was higher at the higher stocking density, while the feed conversion ratio was better at the lower density. Most fish deaths resulted from cannibalism, and losses due to this were 53.8% of the initial stocking density of 350 individuals per liter, and 45.1 % at 250 Individuals per liter. The results indicate that both initial stocking densities produced satisfactory rearing results. It must be emphasized that the final number of fish obtained for further rearing was substantially more at the higher density (350 larvae/l), which suggests this is suitable for practical applications.
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