Growth of Atlantic salmon (Salmo salar) under different regimes of continuous aerobic exercise

Abstract

To ensure the Atlantic salmon aquaculture industry's sustainable growth, the development and implementation of new production strategies is needed. A strategy that has been adopted by the industry to intensify the salmon’s production is the use of closed containment systems (CCS) or semi-CCS to produce larger and more robust smolt before transferring them to open net pens for further growth. These systems allow for controlling the water velocity, which can be used to induce swimming training in Atlantic salmon. This study investigated the effects of two different swimming training strategies in two separate trails (constant training in freshwater and constant training in seawater) on growth performance, muscle fibre development, cellular energy and expression levels of growth factors: igf1, igf2 and the receptors igf1ra1 and igf1ra2 in the Atlantic salmon white muscle tissue. Thus, two trials were conducted. For the constant training in the freshwater phase, a small-scale laboratory trial was conducted, using three different water velocities (0.5 body-lengths per second (BL/s), 1.0 BL/s and 1.5 BL/s). After the freshwater phase, the fish were reared at the same water velocity (0.5 BL/s) in the seawater phase. Atlantic salmon trained at 1.5 BL/s and 1.0 BL/s exhibited significantly higher growth rates than the group trained at 0.5 BL/s after transfer to seawater. Furthermore, the group trained at 1.5 BL/s showed a higher frequency of small muscle fibres. However, the overall gene expression levels did not seem to be affected by the training regimes. The Adenylate Energy Charge (AEC) was stable, indicating sufficient energy in the muscle tissue. For the constant training in seawater-phase trial, Atlantic salmon were trained for about 4 months in two different rearing systems: Preline S-CCS, which has a constant water flow and allows for aerobic training, and an open sea pen. The rearing method did not yield any significant differences in weight or length of the fish. However, notable findings were observed in gene expression, particularly an upregulation of igf1ra2 in the Preline group. The AEC was stable, indicating sufficient energy in the muscle tissue. However, as this trial only covered the post-smolt phase, further investigation is required to fully understand the effects of training during the grow-out phase. The findings from the constant training in the freshwater-phase trial demonstrate that aerobic training during this stage can lead to enhanced growth performance and muscle development. This highlights the potential benefits and opportunities that training regimes can offer when incorporated into existing production strategies. However, to fully understand the physiological impacts and optimize the training strategy on a larger scale, additional studies are required