Fish Welfare - Research IBBG

Numerous species of fish constitute a resource of paramount important to humans. Used in aquaculture, they are a main source of proteins in some developing countries. They are the third most spread group of companion animals. There is also a growing use of these animals for scientific and experimental purposes, as well as in public aquaria. In the last decades, the use of animals has been raising concerns related to their welfare, with implications to the way they are kept and managed in captivity. Legislation has been published to protect animals in captivity and it usually includes fish, despite the relatively little information available concerning their welfare.

The proposed animal welfare concept is based in three main approaches: the organic functioning, the mental experiences and the animals’ nature, which have been integrated and analysed in interdependence. The organic functioning is a fundamental aspect of welfare. Diseases, injuries, poor nutrition are all examples of threats to the organic functioning. But in the core of the welfare concept is the animals’ ability to feel (sentience). This aspect implies the existence of mental experiences which are subjective and of difficult access to the most traditional research approaches. Despite that, there is a body of indirect evidence which allows the attribution of mental states to a number of vertebrate species. The third aspect considered in the welfare is that of animals’ nature. A recent interpretation of this approach highlights not only the need of understanding the animals’ natural behaviour, but mainly how this is related to the animals’ health and to what it wants in each given moment.

The animal welfare definition has recently been applied to fish, namely in numerous studies of aquaculture. Studies of stress and living conditions in aquaculture are among the most common. The psychological component of stress in fish seems to share various components similar to those found in other vertebrates. For example, it was demonstrated that the reaction to aversive stimuli is an integrated process which depends not only of the animals’ perception but also of their learning abilities and past experience memories. These aspects were already studied by some authors using classical and operant conditioning paradigms. However, the existence of mental states in fish, and in particular their suffering capability, is still a source of scientific controversy. Nevertheless, recent literature related to the investigation of pain, reports a fish nociceptive system, opioid-type receptors and analgesia effects similar to those found in the terrestrial vertebrates.

A pre-requisite for the existence of sentience is the ability to form declarative mental representations, which in humans involves the consciousness. These imply the selective attention to internal and external stimuli, anticipatory capacity, expectations, flexible and adaptive responses. The occurrence of these representations in various species of fish in contexts of social interactions, spatial memory and learning has been shown by a number of studies. The underlying neuronal mechanisms, and those related to emotional processes, also suggest a high degree of specialisation and functional similarities with the terrestrial vertebrates. Homologies seem to occur between the telencephalic medium pallium of fish and the tetrapods’ amygdala, and between the telencephalic medium pallium and the hippocampus.

The investigation of memory involving declarative representations was undertaken in various species, revealing important facts related to the occurrence of consciousness. One of such studies involved the search of episodic memory in European scrub-jays (Aphelocoma coerulescens). In relation to a single caching episode, these birds were shown to process information simultaneously related to when, where and what kind of food items were cached. Such flexible and integrated memory features remain to be demonstrated in other animal species.

One of the most relevant aspects in the animal welfare science is the understanding of what the animal wants, i.e., its motivation and preferences. This line of research requires some procedural and interpretative cautions, but can be very informative in relation to what resources or behaviours effectively contribute to the animals’ perception of its welfare in captivity. Some authors also defend that the expression of an animals’ preference or motivation does not necessarily implies consciousness, but – by analogy arguments with humans - can give some light on their mental states.

Currently we have one PhD project within this research line:

- “Welfare in teleosts: behavioural, cognitive and physiological aspects”, SFRH/BD/16162/2004.

This research intends to develop a methodology to study fish motivation, as an expression of fish welfare. For this purpose, other behavioural and physiological parameters (cortisol, glucose, etc.) will be also studied in relation to specific resources perceived as relevant to the fish behaviour. In the scope of the same project, it is intended to study some perceptive factors that may be involved in the activation of the stress response. It is expected that the results of this study may contribute to improve good practices with fish in captivity.

Another research area is foreseen in relation to the investigation of episodic memory in fish, as this approach can constitute a very fruitful contribution to the question of fish suffering (consciousness), with direct implications to its moral status.

The possibility of sentience in fish imposes an ethical approach in what regards to their use as experimental animals. In the scope of the 3 R’s approach, an effort is done to reduce to maximum invasive procedures. One of such examples is the measurement of steroid hormones in fish using non-invasive methods (e.g. holding-water, faeces, or urine).

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