Effects of rearing temperature on the thermal tolerance, metabolic capacity and stress response of cultured lumpfish (Cyclopterus lumpus)

Abstract

Lumpfish (Cyclopterus lumpus) mortalities have been reported during the summer at some North Atlantic salmon cage-sites where they serve as ‘cleaner fish’. To understand their physiology, and whether limitations in their metabolic capacity and thermal tolerance can explain this phenomenon, I compared the aerobic scope (AS) of 6°C-acclimated lumpfish using a critical swim speed (Ucᵣᵢₜ) test, a critical thermal maximum (CTₘₐₓ) test (rate of warming 2°C h⁻¹) and a chase to exhaustion. The Ucᵣᵢₜ and CTₘₐₓ of 45-75g lumpfish were 2.36 ± 0.08 body lengths s⁻1 and 20.6 ± 0.3°C, respectively. The AS of lumpfish was higher during the Ucᵣᵢₜ test (206.4 ± 8.5 mg O₂ kg⁻¹ h⁻¹) vs. that measured in either the CTₘₐₓ test or after the chase (141.0 + 15.0 and 124.7 ± 15.5 mg O₂ kg⁻¹ h⁻¹). Next, I examined whether changing temperatures during incubation/rearing influenced the lumpfish’s AS, CTₘₐₓ and ITₘₐₓ (incremental thermal maximum, measured by warming at 0.1-0.2°C day⁻¹), and stress physiology. Temperature combinations included 6°C/9°C (that used in standard production protocols), 8.5°C/9°C, 6-11°C/9°C, 8.5°C/9-11°C and 6-11°C/9- 11°C, with ranges indicating stochastic changes. The lumpfish’s upper thermal tolerance (CTₘₐₓ, 22.85 ± 0.12°C; ITₘₐₓ, 20.63°C) and AS were not influenced by incubation or rearing temperatures, and based on these values it does not appear that cage-site mortalities during the summer are related to high water temperatures.