Dissolved oxygen (DO) levels were monitored in two marine Atlantic salmon (Salmo salar L.) cage sites on the south coast of Newfoundland (Canada) during the summer and fall of 2008 and 2009. In 2008, sites A and B had cages with stocking densities of approximately 9 kg m À 3 . In 2009, site A was being fallowed while stocking density at site B was of 10 kg m À 3 . During 2008 and 2009, few hypoxic events (de¢ned as DO o6 mg L À 1 O 2 ) were recorded at site A; however, at site B intermittent hypoxic events (46 mg L À 1 O 2 ) were observed. Our study provides a description of intermittent hypoxia occurring in salmon cages. These hypoxic events occur mostly during the summer season and last for as long as 2.5 months. Fish swimming behaviour show that water layers exhibiting low DO did not cause avoidance behaviour. This con¢rms results found by other authors. Site B exhibited low water currents below 5 m suggesting that caution should be taken before considering an increase in stocking densities in cages. Questions remain about the e¡ect of this intermittent hypoxia on ¢sh health and growth, and will be the focus of future research.

Coastal aquaculture has experienced substantial growth in the last few decades and associated impacts on natural environments are of increasing importance. Understanding both the effects of aquaculture on marine ecosystems and the processes of recovery during fallowing periods is crucial for the development of a more environmentally sustainable industry. Because bacteria are sensitive to environmental change, surveying fluctuations in bacterial communities is a promising tool for monitoring the status of benthic environments. Here, we used 16S rRNA gene high-throughput sequencing to characterize bacterial communities in flocculent matter samples collected over a period of 3 years and at various distances from cages (0–200 meters) at production and fallow (3–35 months) salmon aquaculture sites in southern Newfoundland to evaluate the environmental impact of aquaculture on predominantly hard-bottom substrates. Bacterial composition analysis revealed four clusters, three of which (defined as “recently disturbed,” “intermediate impact,” and “high impact”) differed markedly from a fourth “low impact” cluster that contained far-field samples collected >500 m from cages. Samples within the high impact group were most often collected directly under cages, whereas those in the intermediate impact group were mainly sampled from 20 to 40 m from cages. Large scale phylum shifts (increases of Bacteroidetes, Firmicutes, Spirochaetes, and decreases in Proteobacteria and Epsilonbacteraeota) and a decline in bacterial diversity were observed in the high impact cluster, indicating significant ecological change. Samples from sites of different fallow duration were found in the high impact cluster, indicating a lack of recovery, even after 35 months of fallowing. Finally, we identified 28 genera as bacterial biomarkers, specific to one or more clusters, including genera associated with organically enriched environments and previously reported in the context of aquaculture impacts. Tracking the relative abundance of biomarkers in relation to different lengths of fallowing in the three more impacted clusters showed that these markers remained significantly above low impact cluster levels at all times, further pointing toward incomplete recovery. Our results suggest that coastal aquaculture on hard-bottom substrates is prone to long lasting impacts on bacterial communities, especially below cages, and that effects can be accurately tracked using bacterial community profiles or specific biomarkers.

A new opportunistic annelid (Ophryotrocha cyclops) discovered on benthic substrates underneath finfish aquaculture sites in Newfoundland (NL) may be involved in the remediation of organic wastes. At those aquaculture sites, bacterial mats and O. cyclops often coexist and are used as indicators of organic enrichment. Little is known on the trophic strategies used by these annelids, including whether they might consume bacteria or other aquaculture-derived wastes. We studied the lipid and fatty acid composition of the annelids and their potential food sources (degraded flocculent organic matter, fresh fish pellets and bacterial mats) to investigate feeding relationships in these habitats and compared the lipid and fatty acid composition of annelids before and after starvation. Fish pellets were rich in lipids, mainly terrestrially derived C18 fatty acids (18:1ω9, 18:2ω6, 18:3ω3), while bacterial samples were mainly composed of ω7 fatty acids, and flocculent matter appeared to be a mixture of fresh and degrading fish pellets, feces and bacteria. Ophryotrocha cyclops did not appear to store excessive amounts of lipids (13%) but showed a high concentration of ω3 and ω6 fatty acids, as well as a high proportion of the main fatty acids contained in fresh fish pellets and bacterial mats. The dorvilleids and all potential food sources differed significantly in their lipid and fatty acid composition. Interestingly, while all food sources contained low proportions of 20:5ω3 and 20:2ω6, the annelids showed high concentrations of these two fatty acids, along with 20:4ω6. A starvation period of 13 days did not result in a major decrease in total lipid content; however, microscopic observations revealed that very few visible lipid droplets remained in the gut epithelium after three months of starvation. Ophryotrocha cyclops appears well adapted to extreme environments and may rely on lipid-rich organic matter for survival and dispersal in cold environments.

In Newfoundland and Labrador (hereafter, Newfoundland), all farmed Atlantic Salmon Salmo salar originate from the Saint John River, New Brunswick, strain, raising the question of potential impacts of escapees on wild, genetically distinct stocks. Unfertilized eggs of farmed and wild salmon were assessed for diameter, mass, adenosine triphosphate (ATP) content, and fertilization success, this is the first study to assess ATP content in Atlantic Salmon eggs. Results demonstrated that farmed salmon egg mass (0.1046 g), diameter (6.2 mm), and ATP content (0.0281 nmol/egg) were significantly lower than the same characteristics in wild salmon. Among and within females, variability in egg size was similar in both wild and farmed groups. This study lends some evidence to the fact that in the Newfoundland context, eggs of escaped farmed salmon may be less likely to produce viable, large larvae compared with their wild counterparts.

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.