Effectiveness of eugenol sedation to reduce the metabolic rates of cool and warm water fish at high loading densities

Effects of eugenol ( AQUI ‐S ® 20E, 10% active eugenol) sedation on cool water, yellow perch P erca flavescens ( M itchill), and warm water, N ile tilapia O reochromis niloticus L. fish metabolic rates were assessed. Both species were exposed to 0, 10, 20 and 30 mg L −1 eugenol using static respirometry. In 17°C water and loading densities of 60, 120 and 240 g L −1 , yellow perch controls (0 mg L −1 eugenol) had metabolic rates of 329.6–400.0 mg O 2  kg −1  h −1 , while yellow perch exposed to 20 and 30 mg L −1 eugenol had significantly reduced metabolic rates of 258.4–325.6 and 189.1–271.0 mg O 2  kg −1  h −1 respectively. Nile tilapia exposed to 30 mg L −1 eugenol had a significantly reduced metabolic rate (424.5 ± 42.3 mg O 2  kg −1  h −1 ) relative to the 0 mg L −1 eugenol control (546.6 ± 53.5 mg O 2  kg −1  h −1 ) at a loading density of 120 g L −1 in 22°C water. No significant differences in metabolic rates for N ile tilapia were found at 240 or 360 g L −1 loading densities when exposed to eugenol. Results suggest that eugenol sedation may benefit yellow perch welfare at high densities (e.g. live transport) due to a reduction in metabolic rates, while further research is needed to assess the benefits of eugenol sedation on N ile tilapia at high loading densities.