Low temperatures typical of winter cage-site conditions in Atlantic Canada impact the growth, physiology, health and welfare of Atlantic salmon (Salmo salar)

Vadboncoeur, Émile (2023) Low temperatures typical of winter cage-site conditions in Atlantic Canada impact the growth, physiology, health and welfare of Atlantic salmon (Salmo salar). Masters thesis, Memorial University of Newfoundland.

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Abstract

Limited research has been conducted on the physiology of Atlantic salmon (Salmo salar) at cold temperatures despite significant mortalities during the winter at sea-cages in Atlantic Canada. Thus, in this thesis, I exposed post-smolt cultured Atlantic salmon to a seasonal decline in temperature from 8 to 1°C (at 1°C week-1), and a ‘cold-shock’ from 3 to 0°C for 4 or 24 hours. During the seasonal decline in temperature, feeding decreased starting at 6°C (and ceased by 1-2°C), osmoregulatory changes and increases in heat shock protein expression began at 4-5°C, and at 1°C elevated plasma cortisol levels indicative of mild stress were measured. The ‘cold-shocks’ resulted in a relatively small stress response (i.e., increases in plasma cortisol and glucose), but no other adverse effects or mortalities. Nonetheless, a number of mortalities/moribund fish were noted when various groups of Atlantic salmon were held for long periods at < 8°C. Moribund fish were lethargic and swam erratically, had enlarged livers and plasma enzymes suggestive of liver damage, and developed ulcers to the head/jaw. The former symptoms are indicative of ‘Winter Syndrome’ described in gilthead sea bream (Sparus aurata) aquaculture, and these ulcers have previously been observed in Norway and associated with tenacibaculosis.

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