The effect of intermittent hypoxia on growth, appetite and some aspects of the immune response of Atlantic salmon (Salmo salar)

Abstract

To assess the impact of moderate intermittent hypoxia (dissolved oxygen, DO, 4.0–5.9 mg L−1 O2) on Atlantic salmon growth, food intake, appetite control and innate immunity, a 47‐day study mimicking DO conditions observed in sea cages was conducted (hypoxic events occurring on average 3.5 times day−1 and with a mean duration of 69 min). Three treatment groups were studied: normoxia (N), hypoxia fed (HF) and hypoxia feed restricted (HFR). Initial mass and length were measured at the start of the experiment, and sampling was performed at 22 and 47 days. Hypoxia had no effect on the mRNA expression of the appetite regulating factors neuropeptide Y (NPY) and cocaine and amphetamine regulated transcript (CART) measured at day 47. The HF salmon ate 24.8% less between days 22 and 47 as compared with the N group, which was associated with a 23.6% lower overall growth rate by the end of the experiment. Head kidney leucocyte respiratory burst was significantly lower in the hypoxic groups suggesting a negative impact of hypoxia on leucocyte function independent of feeding level. Our results suggest that moderate intermittent hypoxia observed in sea cages in the summer‐fall might reduce fish mass gain, and compromise aspects of the innate immune system.

Cage size affects dissolved oxygen distribution in salmon aquaculture

“…Failure to account for local DO conditions can result in reduced feed intake and growth, increased susceptibility to disease and, in extreme cases, mortality (Remen et al 2012, 2014, Burt et al 2013. Our results confirm the expectation that DO levels are lower in larger cages, but also demonstrate that larger cage sizes can be used without impacting salmon production performance or welfare when ambient DO conditions are sufficient, such as those recorded throughout this study.…”

“…As DO saturation declines and oxygen becomes metabolically limiting, activities non-essential to immediate survival, including feeding and growth, are minimized (Burt et al 2013, Remen et al 2016. For healthy Atlantic salmon, moderate DO levels, as high as 77% saturation, lead to reduced feed intake (Remen et al 2016).…”

Distinct physiological strategies are used to cope with constant hypoxia and intermittent hypoxia in killifish (Fundulus heteroclitus)

“…This is starkly contrasted by the extensive literature on intermittent hypoxia in mammals, which has uncovered widespread physiological, developmental and genomic consequences that are distinct from continuous hypoxia exposure (Neubauer, 2001;Douglas et al, 2007;Farahani et al, 2008). There is evidence that exposure to repeated bouts of hypoxia compromises growth in some fish species (Atlantic salmon, Salmo salar, and southern catfish, Silurus meridionalis) but not others (spot, Leiostomus xanthurus, and killifish, Fundulus heteroclitus) (Stierhoff et al, 2003;McNatt and Rice, 2004;Burt et al, 2013;Yang et al, 2013). Exposure to daily oxygen cycles has been observed to increase hypoxia tolerance and aerobic swimming performance in hypoxia in southern catfish (Yang et al, 2013), to increase resting metabolism measured in normoxia in summer flounder (Paralichthys dentatus) (Taylor and Miller, 2001), and to reduce red blood cell GTP concentration and increase plasma bicarbonate concentration in carp (Cyprinus carpio) (Lykkeboe and Weber, 1978).…”

Variation in the structure of the water column as captured by Slocum glider CTD and by CTD from a research vessel and assessment of internal waves

“…The ocean conditions in marine aquaculture areas have been known to interact with aquaculture operations [3]. For instance, ocean conditions can affect fish growth [9] [6], fish behavior [26], decision on site selection [18], outbreaks and transport of infectious disease [38] [2], and dispersion of fish farm particulate wastes [39].…”