Introduction
One of the few enrichment opportunities in commercial aquaculture facilities to boost fish growth, health and welfare is water flow enhancement. Particularly fast-growing athletic species with high metabolic demands for oxygen such as yellowtail kingfish grasp the benefits of flow enrichment and the associated swimming exercise (Palstra et al., 2015, 2024). This study aimed at establishing the physiological effects of water flow enrichment on yellowtail kingfish in commercial marine RAS production tanks.
Materials and methods
In the enriched flow tank (regular dodecagon with a volume of 62 m3), flow was generated by a propellor and speeds ranged between 70-75 cm.s-1 in the outer curve down to averages of 18-29 cm.s-1 near an inner placed ring (Fig. 1). As a result, fish (N= 400 per tank as part of a total of 4,000 fish per tank; initial body-weight ~160 g) could swim at their preferred swimming speed where the maximum was optimal for fish at the start of the trial. The flow in the identical regular flow tank ranged from 13-17 cm.s-1 down to averages of 6-10 cm.s-1.
Overall Dynamic Body Acceleration (ODBA) was monitored with implanted acoustic transmitters with accelerometer sensors over the first three months (up to a BW of ~1,200 g) and used to demonstrate the increased activity of fish in the enriched flow tank vs. the regular flow tank (N=10 sentinel fish in each tank). Flow enrichment effects on growth, blood parameters, fillet quality and white muscle transcriptomics were determined after seven months (BW ~2,600 g).
Results and discussion
ODBA levels were 34% higher in the flow enriched production tanks (Fig. 1) where fish were most active at 7-8 h in the morning. The higher activity levels were supported by higher plasma glucose levels. Under enriched flow, less fish died (36% less than in the tank with regular flow), fish grew faster (10% during the first two months) and more homogenous, and fish had a leaner body shape (lower body height index). Fillet quality data are currently being analyzed while RNAseq data showed up-regulated keratin expression supposedly reflecting increased firmness.
Overall, we can conclude that flow enrichment is beneficial for growth and welfare of yellowtail kingfish in commercial marine RAS production tanks, thereby validating the earlier experimental-scale results (Palstra et al., 2015). If flow speeds could be further increased with increasing fish size, benefits may be more significant along the whole on-growing period. Acoustic sensortags with ODBA settings provide valuable information about the activity of the fish which could be extended to a digital twin model for energy expenditure and useful for precision farming.
Acknowledgements: This study received funding as public-private partnership from the Dutch Ministry of Agriculture, Nature and Food Quality and The Kingfish company (grant number LWV20.37).
References
Palstra, A.P., Mes, D., Kusters, K., Roques, J.A.C., Flik, G., Kloet, K., Blonk, R.J.W. (2015) Forced sustained swimming exercise at optimal speed enhances growth of yellowtail kingfish (Seriola lalandi). Frontiers Physiology 5:506
Palstra, A.P., Abbink, W., Agbeti, W., Kruijt, L., Jéhannet, P., Lankheet, M. (2024) Heart rate and acceleration dynamics during swim-fitness and stress challenge tests in yellowtail kingfish (Seriola lalandi). Biology 13(3), 189