by IGB
Crustaceans such as shrimp are a popular food. Due to the high demand for crustaceans, the majority of those consumed no longer come from the wild, but are farmed on a large scale in aquaculture. This is particularly the case for shrimp, which has seen production almost double in the last decade. However, there is potential for improvement in terms of sustainability and animal welfare.
The dilemma is that too little is known about the sensitivity and stress response of these decapod crustaceans, which are invertebrates and therefore have a different status to vertebrates in the Animal Welfare Act (TierSchG) and other standards.
With this in mind, researchers from IGB and the Alfred Wegener Institute are developing an assessment system for improved animal welfare and animal health in shrimp farming, supported by the Deutsche Bundesstiftung Umwelt. The scientists have recently brought together the current state of knowledge on this topic and published a review article. In an interview, lead investigator of the study Dr Sven Würtz explains why aquaculture practitioners should address this issue with urgency.
Mr Würtz, what are crustaceans and what role do they play in our diet?
For the purposes of human consumption, creatures belonging to the order of decapods are commonly referred to as crustaceans. They include not only shrimp, but also lobster, crawfish, crayfish and crab. Shrimps are one of the most widely consumed aquaculture species in Germany, weighing in at around 1.1 kilograms per capita per year. Most are produced in open pond systems in other countries, especially in Southeast Asia. Total global yield is around 5 million tonnes per year.
When surveyed, consumers say that they attach increasing importance to transparency, environmental protection and animal welfare. Is there a positive development in shrimp farming on this front?
There is, in fact, a large discrepancy between consumers’ increasingly explicit demand for animal welfare and the level of knowledge about animal welfare in production. We produce larger and larger amounts of shrimp without knowing anything about their welfare – there is a wide gulf between ambition and reality in this respect. Evaluation systems and standards for transparency and environmental performance have emerged in recent years, but there are none in place for animal welfare and animal health in crustacean farming.
This is a fundamental problem in aquaculture, due in part to its great diversity: over 400 different aquatic organisms are farmed in aquaculture. There is very little specific information on welfare for most species, despite the fact that the needs of these creatures can differ significantly. In fact, there are no scientific publications on animal welfare for almost two-thirds of these species in aquaculture. It is therefore virtually impossible to satisfy consumers’ need for information. There is also little guidance available for crustacean farmers, who have the potential to provide better animal welfare.
But there are defined standards for other farmed animals, such as a minimum space requirement. Why are crustaceans treated differently?
The European Commission called for measurable animal welfare indicators in its Animal Welfare Strategy to reinforce good animal welfare practices based on scientific evidence, but invertebrates have so far been excluded from this policy. The European Parliament adopted the “Farm to Fork” resolution, which also calls on the Commission to support and promote the development of higher animal welfare standards for marine invertebrates such as decapod crustaceans. In the UK, decapod crustaceans are recognised as being “sentient”, and legislative changes are being made accordingly.
Does the sentience of crustaceans really differ to that of vertebrates?
Scientists are undecided as to whether or not decapod crustaceans experience pain. Crustaceans have a reflex response to avoid things that cause harm. However, there is a fundamental difference between the reception of a noxious stimulus – referred to as nociception – and pain: whereas nociception is purely physiological, pain has an additional emotional component. By definition, pain requires the brain to process the noxious stimulus. If, then, the stimulus is processed in the brain and associated with a negative experience, the animal will try to avoid that stimulus in the future. This is more than just a reflex response. Avoidance learning is a clear criterion of an animal’s capability to feel pain.
The question of whether animals have feelings of pain and suffering can only be assessed by analogies with humans. Inevitably, it is not possible to ultimately answer this question. The question of whether decapod crustaceans feel pain or suffering is therefore a highly contentious issue. In my opinion, however, the lack of definitive proof is not the decisive factor. After all, the point is to ensure optimal husbandry and to identify the necessary evaluation criteria. This is what we want to establish as standard practice in the CrustaWohl project.
Which evaluation criteria are appropriate for crustacean aquaculture?
Stress response is also directly related to welfare. Stress can be assessed much more objectively than pain. From a biological perspective, stress is nothing negative per se – it is simply an indication that the organism is trying to reach a new state of equilibrium after exposure to stress, to adapt to a new situation. In the case of prolonged stress, however, the various adaptation responses are detrimental to health and other important bodily functions. For example, immune defence, growth or reproduction may be impacted. This type of stress is then referred to as “distress”.
If, then, you want to assess animal welfare, you can also analyse stress parameters. Although crustaceans have different hormonal systems to vertebrates, the effects of distress are very similar. The metabolism changes, which can be measured by determining levels of glucose, lactate and glycogen, for example. These are signs that energy reserves are being mobilised. After a prolonged effect of the stress factor, we can then see changes in the animal’s performance, such as stunted growth, reduced resistance to disease or changes in behaviour. One of the tasks of CrustaWohl is to identify easily measurable physiological assessment criteria and methods for this.
We also see great potential in the assessment of behaviour. After all, we now have highly automated tracking methods that can be used to detect anomalous behaviour in animals. But it goes without saying that the best type of stress is having no stress at all, which is why we also focus on the precautionary principle and develop husbandry recommendations.
In other words, avoiding stress in the first place?
Exactly! This can of course be achieved by taking general measures such as providing optimal water quality and good food, and ensuring appropriate stocking density. But in order to identify additional parameters, we must look at the issues of breeding, rearing, harvesting, transport, stunning and species-appropriate slaughter separately. In shrimp farming, for example, there is a method called “eyestalk ablation”, which involves removing the eyestalks of female shrimps in order to accelerate egg maturation and reproductive drive. Whether this is compatible with animal welfare objectives must of course be thoroughly scrutinised – some aquaculture farms have already abandoned this practice.
Another example is the “stress test” for juveniles in the grow out phase. This involves exposing some animals of a batch of brood to high levels of stress through salt, temperature or chemicals, and then determining the number of survivors. This is done to evaluate the fitness of the hatchlings. Such a crude method is outdated, and this test should be replaced in future by behavioural tests or the use of physiological markers.
The harvest phase is definitely one of the most stressful moments for the creatures. For this reason, there should be a stronger focus on appropriate stunning techniques. Thermal shock is generally a good method for stunning crustaceans because it does not activate their nociceptors.
A direct question: In your opinion, is it possible to eat crustaceans with a clear conscience?
There is a global demand for crustaceans, and they will be farmed anyway. That is the social reality. We try to do our bit by exploring how best to ensure animal welfare. If you choose to eat crustaceans, be sure to look for an organic label. By doing so, you can help protect mangroves and support more species-appropriate husbandry.
Contact
Sven Würtz
Research Group Leader
Research group
Molecular Fish Physiology
Reference (open access)
Sven Wuertz, David Bierbach, Mirko Bögner, “Welfare of Decapod Crustaceans with Special Emphasis on Stress Physiology“, Aquaculture Research, vol. 2023, Article ID 1307684, 17 pages, 2023. https://doi.org/10.1155/2023/1307684
