Introduction

Every year millions of fish are reared for food. The slaughter of these fish should be carried out in a way that causes no unnecessary pain or suffering. In recent years various systems have been developed in an attempt to achieve this. The key principle of humane killing is to render the fish immediately unconscious and insensible to pain, a condition that must persist until they are dead.

Historically, one of the most common methods for stunning or killing fish was to use a priest (a truncheon-like instrument). In 1999 automated stunning systems for administering the stun were introduced and first used in the industry. Although the majority of fish are killed by the initial sharp blow to the head, either by a priest or automated mechanical methods, there is a small chance that some may be ineffectively stunned. Therefore, when using these systems, it is imperative that staff can recognise effective stunning and know how and when to re-stun if necessary.

Whilst it may appear that percussive stunning is a straightforward procedure, great care must be taken in the operation, as both operator error and/or equipment failure will severely compromise animal welfare (and affect product quality).

Methods for commercially stunning and killing fish by electricity in the UK were initially developed in the late 1990s. Electrical methods can be divided into two types: stunning only (electronarcosis), where the stun is quickly followed by a method of killing; and stun/kill (electrocution), where fish are rendered permanently insensible by an electrical current, so there is no need, for welfare reasons, to follow up with any other procedure.

These guidance notes explain the theory, practice and use of the different methods of stunning and slaughter currently used in the industry. They provide essential technical information for everybody involved in the handling and slaughter of salmon and trout, including the slaughter teams, supervisors, veterinary surgeons and maintenance engineers. They provide operators with background information to help them carry out their job safely and competently and explain how pre-slaughter handling can affect carcase quality.

The Humane Slaughter Association (HSA) is aware that research into humane slaughter of farmed fish is still ongoing and there are some fundamental technical issues that remain to be resolved for some species. This booklet represents current industry best practice. It will be regularly reviewed and updated to incorporate new developments and information.

The guide also outlines a number of methods used in some parts of the industry that the HSA cannot recommend due to welfare concerns. The HSA actively encourages producers to move towards using modern humane practices as soon as possible.

Please do not read further if you feel you may be negatively affected by the content.

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