Do fish feel pain?

Whilst the memory of a fish is famously said to be just three seconds, some interesting evidence today showed that fish show conditioning qualities, and learn to avoid adverse stimuli. 

Seems more than a three second memory to me.. shocking :D. 

Anyway, the lecture I had today, was on FISH WELFARE. From the offset I was prepared to be slightly bored in this lecture with having much less of an interest in fish compared to other species. However, as with my diverse species lectures in second year (where we learnt about the rather clever adaptations of fish to different environments), I was actually pleasantly surprised and the lecture was rather interesting! 

I thought I'd share points of the lecture here.

Fish Welfare

The lecture was given by the humane slaughter association. They are an association which was founded in 2011. They are a charity, and specialise in the welfare of animals farmed for food at the time of slaughter and transport. 

Why is welfare important?

• Scientific research- animal stress and pain alongside animal health (disease, growth and fertility).
• Ethical/moral reasons.
• Legislation- owners of the animals are responsible for their welfare.
• NGOs, codes of practice and consumer groups.
• Meat quality- the more stressed the animal before slaughter, the worse the product at the end.
• Demands of the retailer for welfare.
• Public perception.
• Health and safety- a tuna fish can grow to the size of a shark. Not something you want to be in the water with.

Current Evidence That Fish Experience Fear & Pain

1. Nociceptors can detect heat, toxins and pressure. In mammals, above or below certain thresholds, these signals are known as pain.
2. Neurones convey nociceptive signs to the BRAIN. This shows that the response is not a reflex arc as the higher thinking and processing centre is involved.
3. Behavioural evidence- species specific:

• Trout learn to avoid adverse stimuli e.g. nets.
• Trout injected with acid rub their snouts and their respiration rate increases.
• Goldfish mediate their responses to noxious stimuli depending on the circumstances.
• Trout challenged with a noxious stimuli ignore novel objects.
• Analgesics reduce pain related behaviour. 

Potential Stress During Harvest 

• Food Withdrawal- it is essential to starve fish for a period of time before harvest because if not the fish foul the water due to stress which increases the carbon dioxide in the water meaning the fish slowly suffocate. However, some places also withdraw food for longer than necessary sometimes stretching to weeks, when it is only really necessary to starve the fish until the gut is empty. 
• Rising stocking density. 
• Decreased Oxygen. 
• Abrasions.
• Increased light intensity- correlated to predators. 
• Human presence (predator).
• Removal from water.
• Ineffective stunning/killing. 

Fish Carcass Downgrading 

External:

• Eye damage.
• Bruising/cuts.
• Scale loss.
• Net marks.

Internal:

• Early rigor- depletion of glycogen quicker in the muscles and conversion to lactic acid due to stress.
• Gaping.
• Flesh texture/colour.
• Haemorrhages.
• Blood splash/spots.

Legislation

Currently, fish are only covered by minimal protective slaughter legislation. The new legislation which was from January 2013- PATK (protection of animals at time of killing) states:

'Fish should be spared avoidable stress, pain, and suffering. There are no specific provisions.' 

EU legislation to protect fish further is expected within the next ten years.

Fish Slaughter

Can slaughter be humane?

• Killing without aversion or pain.
• Goal= make the animal unaware of the surroundings, and unable to feel fear/pain. This is achieved when the animal becomes unconscious through correct stunning. 
• To ensure death non fatal stunning should be followed by a killing method. This prevents the animal recovering from a stun. For slaughter to be humane the animal must remain in a stunned state until death occurs.
• Performing killing without stunning will cause fear and pain.

How to assess effective stunning:

• Brain waves.
• The rhythmic opening of the operculum and gill flap= signs of beginning to regain consciousness.

Types of stunning:

• Wet pipeline stunning electrical- made according to the type of fish. Electricity flows around and through the fish. Need to consider the electric field, frequency and duration of stun for immediate, effective and prolonged stunning. Dependent on number of fish, type, stress levels and many other factors. How to assess an effective electric stun:

1. Fish swim as normal before application.
2. Fish rigid as current applied.
3. Loss of balance & fish turns upside down.
4. Eye movement stops.
5. No rhythmic opercular movement.
6. Small involuntary twitches and tail may flutter.
7. No reaction to tail pinch.
8. Vestibulo-ocular eye reflex (eye roll when turn fish head) absent. 
9. Differentiate from agonal gasping.

• Percussive Stunning- Manual vs automated. Similar to mammal captive bolt stun. Aims to transfer sufficient energy into the brain to interrupt normal brain function and induce unconsciousness until death. Target area= top of head. 

Poor welfare methods:

• Asphyxiation in air- left out to die on the side of a bank etc.
• Death in ice slurry.
• Live Chilling- normally paralysed at evisceration not dead. 
• Gill cut without prior stunning.
• Carbon dioxide narcosis- very stressful.
• Decapitation- used in eels, but brain function still there for 10 minutes afterwards.
• Salt/ammonia bath- acts on mucosal surfaces. 
• Electro-immobilisation- current in electrial stunning not enough for death, results in paralysis.

Bleeding fish:

• Sever the gill arches.
• If not bled such as portion trout, iced water is commonly used in harvest bins. You should use iced water only to avoid chance of recovery as water is oxygenated.
• Turbot and Halibut fish must be bled immediately after stunning- very resistant to low levels of oxygen due to where they lie at the bottom of the sea bed/tank.