Abstract
Swimming exercise at optimal speed may optimize growth performance of yellowtail kingfish in a recirculating aquaculture system. Therefore, optimal swimming speeds (Uopt in m s−1 or body lengths s−1, BL s−1) were assessed and then applied to determine the effects of long-term forced and sustained swimming at Uopt on growth performance of juvenile yellowtail kingfish. Uopt was quantified in Blazka-type swim-tunnels for 145, 206, and 311 mm juveniles resulting in values of: (1) 0.70 m s−1 or 4.83 BL s−1, (2) 0.82 m s−1 or 3.25 BL s−1, and (3) 0.85 m s−1 or 2.73 BL s−1. Combined with literature data from larger fish, a relation of Uopt (BL s−1) = 234.07(BL)−0.779 (R2 = 0.9909) was established for this species. Yellowtail kingfish, either forced to perform sustained swimming exercise at an optimal speed of 2.46 BL s−1 (“swimmers”) or allowed to perform spontaneous activity at low water flow (“resters”) in a newly designed 3600 L oval flume (with flow created by an impeller driven by an electric motor), were then compared. At the start of the experiment, ten fish were sampled representing the initial condition. After 18 days, swimmers (n = 23) showed a 92% greater increase in BL and 46% greater increase in BW as compared to resters (n = 23). As both groups were fed equal rations, feed conversion ratio (FCR) for swimmers was 1.21 vs. 1.74 for resters. Doppler ultrasound imaging showed a statistically significant higher blood flow (31%) in the ventral aorta of swimmers vs. resters (44 ± 3 vs. 34 ± 3 mL min−1, respectively, under anesthesia). Thus, growth performance can be rapidly improved by optimal swimming, without larger feed investments.
Highlights
IntroductionThere is a great need to optimize the conditions for fish growth, but without compromising health and welfare
Aquaculture is facing an increasing demand for sustainably produced fish
Cost of transport (COT) and optimal swimming speeds (Uopt) The calculated cost of transport (COT) values were plotted against the swimming velocities as polynomial U-shaped curves for each of the subsequent groups (Figures 2A–C)
Summary
There is a great need to optimize the conditions for fish growth, but without compromising health and welfare. Significant numbers of commercially produced species of fish suffer from impaired well-being and high mortality (e.g., Castro et al, 2011, 2013). This may, at least partly, be explained by the fact that fishes cannot display their normal swimming behavior due to high densities or low water flow. Evidence suggests that the health and welfare of swimming fish is improved, not compromised (Castro et al, 2013; reviewed by Huntingford and Kadri, 2013)
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