Flesh Quality

Although this guide is focussed on fish welfare, post-mortem flesh quality can give a valuable insight into pre-slaughter treatment of the fish. Many flesh quality issues can be greatly reduced by improving pre-slaughter handling. The following section details some common flesh quality problems that can be indicative of welfare problems.

Early rigor

If fish are stressed during crowding they will deplete their energy reserves prior to slaughter and rigor will occur much sooner than when the fish have been crowded carefully. With early rigor the flesh can be difficult to process, reducing both the yield and flesh quality and resulting in a shorter shelf-life. A delayed rigor allows processing to take place before rigor occurs and avoids these associated problems. However, early rigor can also occur when the health status of fish is low, so the reasons for early rigor need to be considered carefully.

Gaping

Increased stress and activity immediately prior to slaughter results in increased lactic acid levels in the muscle tissue. This causes the breakdown of connective tissue between the muscle fibres, resulting in gaping of the flesh. Not only does this make it difficult to cut the flesh, reducing the yield, but it also reduces the appeal of the product to the consumer.

Bruising

This can be seen with percussive stunning, particularly when a priest is used. When slaughter teams become tired the degree of accuracy can deteriorate, resulting in blows behind the head and on the neck, which can cause bruising.

The way in which the fish are delivered to the stun point can also cause bruising: if fish fall or are dropped from the dewaterer or braille, or if poorly maintained and operated pumps and pipes are used.

Haemorrhages

Haemorrhages are caused by blood leaking from blood vessels into the flesh. They are typically seen in the tail region if a fish has been lifted or held tightly by its tail prior to slaughter. Haemorrhages downgrade the fillet and result in a shorter shelf-life.

Haemorrhages can also be caused by poorly-positioned manual percussive stunning and by electrical stunning if the correct parameters have not been used.

Scale loss

When fish are crowded, their environment changes significantly. In a well-run crowd this change is minimal and will have little effect on the fish. However, if the crowd is brought in too quickly, the net pulled too tightly, or the fish are left crowded for too long, they may struggle and damage themselves against the nets and other fish as they try to escape. This can result in a loss of scales as well as other damage. Scale loss can also happen during other procedures, such as grading, but by examining the fish it should be easy to determine when the damage occurred, i.e. whether the damage is recent or not.

Eye damage

Eye damage occurs during percussive stunning when the blow is position incorrectly and either hits the eye directly or close enough for the eye to rupture. Eyes can also be affected by poorly maintained nets.