do fish feel

Do fish feel?
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Last updated: Wednesday, October 03, 2012

We place fish on the hierarchy of sentience somewhere above slugs, and feel better about eating them than we do birds and mammals. But research on fish behaviour and learning suggests we've seriously underestimated them.
Fish have static, expressionless faces; their skin is cold; they have no obvious pulse and they don't call out when they're in distress (not so that we can hear, anyway).
They don't even have much variation in body posture: they thrash about when they're hooked and jerked into an environment where they can't breathe, but they don't flinch or cringe to show they're afraid or in pain.

Image: WWF
All of which makes it easy to conclude that they're nothing like us, and feel nothing. Or nothing much.
But fish have nervous systems similar to other vertebrates, and research into their cognition and behaviour has revealed surprising results.
Does it matter what fish feel?
Lack of injury and disease, and signs of normal growth and behaviour indicates that an animal's welfare is fairly good, but that's not the whole story. Welfare should also involve freedom from physical and emotional discomfort, and a sense of wellbeing. At the most basic level, this means freedom from pain and fear.
Millions of fish are killed (and injured) in order that some can end up on our plates. Fish are now also one of the most commonly used research animals. If they are capable of feeling pain and distress in any way like other vertebrates, then their welfare, as it is with chickens and cows and zoo animals, and all other animals we use for our purposes, should be a matter of moral concern.
The greater their capacity for suffering at our hands, the greater our concern should be.
But are fish capable of suffering, and do they enjoy a sense of wellbeing? Are they capable of learning and memory, both important indicators of sentience? The examples of research findings cited here strongly indicate that they do:
Fish produce neurotransmitters such as endorphins, the function of which is to relieve pain.
In experiments similar to those on rats and mice, fish show that they feel fear, or at least unease, and can learn to avoid negative stimuli. Trout learn that a blue light is the cue for a net being dipped in the water to catch them, and know to swim into the safety of an adjacent chamber when they see the light. They also learn how to press a suspended pendulum that releases a food pellet, much like a rat pressing a lever.
Some fish use sound to communicate distress when they are threatened e.g. when nets are dipped into their tanks. In one experiment, fish grunted when they received an electric shock; what's more, the fish then began to grunt as soon as they saw the electrode.
Blind Mexican cave fish, which rely on pressure changes in the water to detect objects, form a mental map of their surroundings, memorising obstacles within a few hours.
Australian crimson spotted rainbow fish, which learnt to escape from a net in their tank, could remember how to do it again 11 months later.
Carp that have been stressed by angling activities become harder to catch in future. Similarly, paradise fish that experienced a predator attack avoid where this occurred for months.
- Olivia Rose-Innes, EnviroHealth Editor, Health24, September 2012
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