Carol Ann Woody (Principle Investigator), J. Nelson, and Kristina Ramstad

Citation:

Woody, C. A., J. Nelson, and K. Ramstad.  2002. Clove oil as an anaesthetic for adult sockeye salmon: field trials. Journal of Fish Biology 60:340-347. http://www.idealibrary.com/servlet/doi/10.1006/jfbi.2001.1842

Abstract:

Wild migrating sockeye salmon Oncorhynchus nerka exposed to 20, 50 and 80mgl^-1 of clove oil could be handled within 3min, recovered within 10min, and survived 15min exposure trials. Fish tested at 110mgl^-1 did not recover from 15min exposure trials. Response curves developed for induction and recovery time considered the following predictors: clove oil concentration, sex, fish length and depth. A significant positive dependence was observed between induction time and fish length for 20, 50 and 80mgl^-1 test concentrations; no dependence was observed between induction time and length at 110 and 140mgl^-1. Recovery time differed as a function of clove oil concentration, but not fish size. A concentration of 50mgl^-1 is recommended for anaesthetizing sockeye salmon ranging in length from 400 to 550mm at water temperatures averaging 9-10°C. Copyright 2002 The Fisheries Society of the British Isles

Key Words:   clove oil; sockeye salmon; Oncorhynchus nerka; fish anaesthesia

Introduction

Fish that are the subject of research studies are often handled, and as a result may suffer stress.  For example, capture by nets or hook and line, subsequent measuring, fin clipping, collection of scale samples and insertion of identifying tags constitutes a level of handling that will stress a fish.  The level of stress a fish undergoes may affect the animal’s immune response and can make it vulnerable to disease.  To reduce handling stress, biologists use a variety of anaesthetics.  Because we are studying wild salmon that Alaskan Natives may harvest for subsistence, we must use an anaesthetic that is effective and will not leave any harmful residues in the meat of treated fish.   

Two anaesthetics commonly used on fish are carbon dioxide gas (CO₂), and 3-aminobenzoic acid ethyl ester methanesulphonate (MS-222).  Both substances are generally recognized as safe for human intake.  The problem with these two substances is that CO₂ is considered only partly effective, while fish treated with MS-222 must be held for 21 days before release to allow the anaesthetic to leave the fishes body.  Because of these drawbacks, we needed to find an alternative anaesthetis that was both effective and safe for human consumption. 

Methods Clove Oil Experiments 5 concentrations were tested (20, 50, 80, 110 and 140 mg/liter) 8 fish were tested at each concentration 15 minute exposure tests Efficacy Criteria Ability to handle fish within 3 minutes Recover within 10 minutes Survive 15 minute exposure periods

Results

The graph below indicates the relationship between fish length and induction time.  The larger the fish, the longer it took for the anaesthetic to work.  However, at anaesthetic concentrations of 110 and 140 mg/liter, fish were immediately knocked out.  Recovery times (second graph) were variable among groups but averaged about 6 minutes (black line in box) for the 20-80 mg/L concentrations.

Conclusions

Clove oil appears to be an effective anaesthetic for use on migrating adult sockeye salmon.  The test concentrations that best met our efficacy criteria were 20, 50 and 80 mg/liter.  For studies requiring light anaesthesia we recommend 20 mg/liter and for studies requiring heavy anaesthesia such as surgery we recommend 80 mg/liter.  We must caution that clove oil is not currently approved by the FDA as a fish anaesthetic.  Very little is actually known of it's effects on fish physiology, immune response, or olfactory ability.  Biologists using this chemical for anaesthetic purposes should keep this in mind, as clove oil may not be the best alternative to MS222.