Abstract
A longer on-land rearing period of Gilthead seabream Sparus aurata before transfer to sea-cages would allow the farmer to benefit from exercise-enhanced growth, resilience, and robustness as induced by increasing water flow in the tanks. In this study, the physiological effects of flow-conditioning were investigated by subjecting large groups of experimental fish to minimal flow or to flow regimes inducing swimming exercise at 1 or 2 body length (BL) s−1 for a period of 8 months (February–October) in 1,500 L tanks. Fish representing the three treatment groups were then used for: (1) a stress challenge netting test and plasma cortisol measurement (baseline, peaking, and recovery levels), (2) blood plasma measurements of glucose, triglycerides, lactate, cholesterol, growth hormone (GH), and insulin-like growth factor 1 (IGF1), and (3) heart and muscle gene expression of the GH and IGF1 receptors and the muscle transcriptome by deep RNA sequencing (RNAseq). Fish size after 8 months of flow conditioning was 92 ± 27 g body weight (BW) for fish under minimal flow, 106 ± 24 g BW (+15%) at 1 BL s−1, and 125 ± 27 g BW (+36%) at 2 BL s−1. Flow conditioning at 1 BL s−1 provided optimal conditions for growth and uniformity, but also stress (lowest baseline plasma cortisol), robustness (higher condition factor and larger hearts), and energy mobilization (increased plasma glucose). Although flow enhanced growth linearly with swimming speed, also the percentage of lordotic fish increased with exercise, particularly high for swimming at 2 BL s−1. The absence of important differences in plasma GH and IGF1, and expression levels of their receptors in heart and white skeletal muscle, indicated that other factors may be involved in growth enhancement. RNAseq of the white skeletal muscle showed upregulated expression of genes involved in muscle contraction, muscle development and its molecular regulation, and immune genes that may play a role in the muscle repair mechanism. An exercise regime of swimming at 1 BL s−1 can be considered as optimal for farming robust seabream although the increase of skeletal deformities should be avoided.
Highlights
Gilthead seabream (Sparus aurata) is currently the most important species in Mediterranean aquaculture
For both water flows that induced swimming at 1 and 2 body length (BL) s−1, fish were swimming harder than the flow
Flow-induced exercise is beneficial for growth and uniformity, stress, robustness, energy mobilization, and muscle building
Summary
Gilthead seabream (Sparus aurata) is currently the most important species in Mediterranean aquaculture. In case of seabream fingerlings and juveniles, long-term exercise significantly enhances growth performance (Ibarz et al, 2011; Sánchez-Gurmaches et al, 2013; Blasco et al, 2015; Vélez et al, 2016). The mechanical load on the skeleton that exercise brings changes developmental prioritization (Fiaz et al, 2012) and leads to more skeletal mass (Totland et al, 2011; Suniaga et al, 2018) Such body changes may contribute to the fish’ robustness or “the capacity to maintain productivity in a wide range of environments without compromising reproduction, health and wellbeing” (Knap, 2005; Colditz and Hine, 2016). Conclusions will contribute to provide advice to farmers on how to benefit from water flow induced swimming exercise to increase growth and robustness of seabream during an extended on-land rearing period
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