Are Shrimps Sentient?

Evidence of Sentience in Shrimps

There is relatively strong evidence that larger decapod crustaceans (i.e. true crabs) are sentient [9]. Unfortunately compared to larger decapods, penaeid shrimps have barely been studied [1]. It is important, however, that protection of decapods should not be restricted in a way that privileges the most intensively studied laboratory species. Existing legislation, for example, extends protection to all vertebrates using evidence based on generalisations from intensively studied species (such as rats) to relevant species [1].

​Let’s have a look at how shrimps respond in relation to indicators of sentience. Unfortunately, studies of P. vannamei tend to focus on feeding behaviour and production practices such as stocking densities and mating. Therefore, research on motivational trade-offs, and information processing that go beyond habituation and sensitisation are currently missing [10]. The lack of this research is due to an information gap, and does not reflect absence of this phenomena.

​The following is a framework we can use to assess sentience in decapods [1]:

1. Possession of nociceptors - Let's say you accidentally touch a hot stove. Instantly, you will withdraw your hand from the stove.  A simple circuit of neurons saved your hand from a noxious stimulus (the hot stove) and prevented you from a burn.  This is referred to as nociception, named after nociceptors, the sensory receptors that detect the noxious stimuli.

2. Possession of integrative brain regions - Being able to integrate information from multiple different sensory sources.

3. Connections between nociceptors and integrative brain regions - Neural pathways connecting nociceptors to the brain (though it should be noted that the nervous system is organised very differently in elongated species such as shrimps, compared to compact species, such as crabs).

4. Responses affected by potential local anaesthetics or analgesics - If you have been to the dentist, you have probably been applied a substance to numb an area of your mouth so that the dentist can perform a procedure that otherwise would be uncomfortable or painful. That’s an anaesthetic, a substance that creates a lack of feeling. When used locally, anaesthetics reduce any sensation (not only pain) in a target area, while the individual remains conscious. If an animal responds differently to stimuli while under the influence of anaesthetics, this suggests the lack of feeling is mitigating an animal's experience of pain or distress.

5. Motivational trade-offs that show a balancing of threat against opportunity for reward - An animal can make a decision, like avoiding negative stimuli, such as an electric shock, rather than experience a positive stimuli (i.e. their actions cannot be explained by reflexes alone).

6. Flexible self-protective behaviours in response to injury and threat - Guarding, grooming or otherwise tending to an injured body part are protective behaviours [11]. These are typically long term responses to injury, seen over periods of hours and days rather than seconds and minutes. In humans, protective behaviour is often controlled by the conscious feeling of pain, such as avoiding using an injured limb. 

7. Associative learning that goes beyond habituation and sensitisation - If an animal can experience something, learn from it, and then make different decisions in the future, it provides good evidence of sentience. 

8. Behaviour that shows the animal values local anaesthetics or analgesics when injured - For example, learning to self-administer anaesthetics or analgesics, or could learn to prefer a location where these can be accessed, or prioritise obtaining these over other needs (i.e. food) when injured.