Introduction
Pikeperch (Sander lucioperca ) is a top predator of European aquatic ecosystems. It is used as a complimentary fish species in polyculture stocks for bio-melioration. Recirculating aquaculture systems (RAS) , have emerged as vital for rearing pikeperch, with efficiency making it reliable source of the fish aimed for extensive aquaculture and restocking. The intensive culture in RAS, however, can be compromise the physiological balance and health status of reared fish.
Live prey feeding is a common practice in aquaculture to provide fish with a diverse and natural diet, promoting their overall well-being and physiological condition. However, the specific implications of live prey feeding on the health of pikeperch juveniles in RAS systems have not been extensively studied.
By examining the effects of live prey feeding on the health parameters of pikeperch, this study aimed to provide valuable insights into the potential consequences of different feeding practices on the health and welfare of RAS-cultured pikeperch juveniles. Ultimately, it supports the successful acclimatization and survival of pikeperch juveniles in open waters, contributing to the effectiveness of replenishment and conservation of wild populations.
Material and methods
Juvenile pikeperch of RAS origin were produced at the Faculty of Fisheries and Protection of Waters, University of South Bohemia (FFWP, USB). The production method involved a combination of pond culture during early ontogeny (4-50 days post-hatching; DPH) and culture in RAS (50-150 DPH) to facilitate weaning onto dry pelleted feed and subsequent ongrowing. At the time of the experiment, the RAS-cultured fish had a body weight (BW) of approximately 30.7 ± 2.64 g and a total length (TL) of 164 ± 7.86 mm. The experiment was conducted in a recirculating aquaculture system (RAS) equipped with an oxygen reactor, mechanical and biological filters. To evaluate the effect of live prey feeding after eight week feeding experiment with two groups: 1st negative group – fed with artificial pellets and 2nd positive group fed ad libitum with prey fish (Pseudorasbora parva). In total, 30 pikeperch juveniles were dissected at different stages of the experiment for the determination of growth rate, somatic indices, blood haematology, and biochemistry parameters . Ten fish were be sampled at the stocking time to assess the initial health status and the same number of fish at the end of the experiment from both positive and negative control groups.
Results and discussion
Pikeperch juveniles fed with pellets had comparable final body weight and SGR with the fish fed on live prey (Table 1) . This indicates that the pellet feed provided similar growth results to the live prey. Similarly, the total length of fish fed with live prey was significantly higher compared to fish fed with pellets. This suggests that the fish fed on live prey experienced greater overall growth and development . Hepatic somatic indices and visceral fat indices were significantly lower in fish fed with live prey. This implies that the fish fed on live prey had lower liver and visceral fat content, indicating a potential difference in metabolism between the two feeding groups.
Analysis of biochemical indices showed significant differences between experimental groups (Table 1). Values of TP were significantly lower in juveniles fed on live prey. This suggests that the fish fed on live prey had lower levels of TP , indicating a potential difference in dietary protein intake and utilization between the feeding groups. Values of GLU were the lowest in the fish fed with pellet feed. This indicates a potential difference in carbohydrate metabolism and the baseline level of the stress between the two feeding groups. Fat metabolism was significantly influenced by live prey feeding. T he fish fed on live prey had altered lipid metabolism, as evidenced by the differences in CHOL , ALB , and AST levels. The values of NH3 in the blood plasma of fish fed on live prey was the lowest, indicating a potential difference in protein metabolism and waste excretion between the two feeding groups.
In summary, the study findings indicate that feeding pikeperch juveniles with live prey resulted in improved growth ( BW, TL, SGR ), lower HSI and VSI , and potential differences in protein, glucose, and lipid metabolism compared to fish fed on pellet feed. Overall, the findings of this study suggest that transitioning pikeperch from pellet feed to live prey before their release into open waters can potentially lead to enhanced growth, and metabolism. These considerations are important for successful restocking programs and the overall sustainability of pikeperch populations into open waters.
Acknowledgements
The study was supported by the Ministry of Agriculture of the Czech Republic, project NAZV QK23020002.
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