Can Zebrafish Needs Be Met In Captivity?

Zebrafishes — small striped fish normally found in the wild in Indian rivers — are now being used globally in biomedical research. In labs, zebrafish are usually kept in conditions that are very different from their natural habitat. Most countries have no legal protection for fish welfare, apart from in Europe, which now has laws to protect fishes used in research, and in farming. 

Zebrafish behavior in the wild, or even in semi-wild environments, has not been studied much, which makes providing any enrichment to their captive lives — or even understanding how captivity affects them — difficult to say the least. In this review, the authors cover research done so far on the social behavior of zebrafishes, mostly in labs, and recommend studying natural zebrafish behavior. Of interest to advocates, the review is meant to help us to understand the suffering involved in keeping these fish in unnatural settings such as labs, which limit and change their behavior, and to improve their welfare in those settings.

Zebrafish Behavior 

There is growing evidence to show that fishes are aware of their surroundings, are intelligent, and can feel pain. They have good cognitive abilities, which means that they have the mental capacity to learn and solve problems. For example, fishes can learn how to use a maze to find food or reach others in their group. They can learn how to change their movements to reach food that is put in different parts of a tank, and they can remember this pattern. They can even teach new fishes in the group how to find food. This evidence shows that their social needs can be complex. 

Reacting to stress is believed to be a psychological response in animals who can think and assess situations. In the same way that other animals can get fever due to stress (called ‘emotional fever’), fishes, who cannot regulate their body temperature, can react to stress by moving to warmer temperatures. Fishes can take a long time to move back to their usual environment, which could mean that confining them could be particularly stressful. 

There is evidence that fish can also feel pain – they try to avoid it, and look for pain-killers when needed. Also, if they have to choose between an enriched area or a barren area that contains pain-killers, a fish who has been hurt prefers the barren area. Fishes can suffer from both physical and psychological pain. 

Keeping animals in small, unchanging spaces does not allow them to behave naturally. It is likely that zebrafishes have a much larger range of behaviors than is currently known. For example, in a large enriched area, they dig out space under artificial plants, swim around the area and circle each other, and show other breeding behaviors that aren’t otherwise seen. 

Zebrafishes are aware of their surroundings and need to explore their surroundings in the wild, as this is important for finding food and reproducing. In places like labs, the lack of a stimulating environment could be particularly stressful for zebrafishes. 

How Zebrafish Are Kept In Labs

Zebrafishes are commonly used in labs in many areas of human biomedical research, and are also used to study pain in animals, with the potential to replace rodents as the main animal model for pain. Zebrafish behavior can change because of experiments, such as restricting breathing, or moving the fish to other surroundings, something that causes particular stress and fear. 

Zebrafishes in labs are usually kept in barren, overcrowded tanks. These have white or clear walls, with nothing to explore and nowhere to hide. This is said to be done to try and clean the space easily, prevent disease, and maintain similar behavior across different groups of fish. However, the main reason appears to be to keep costs low. 

A barren environment can cause stress, strange behavior, damaged brain function, greater aggression, reduced immunity, and lower growth. The situation can be improved by enriching the space, with gravel, sand, plants, and places for them to hide or be alone. Instead of just adding new things to the space, we need to look at how zebrafishes behave to find out what is important to them, and then improve the space accordingly. 

Even after many generations have been born in captive conditions, such as labs, animals still go back to their original behaviors if given the chance. Therefore, natural behavior must be taken into account when improving the welfare of animals in labs. 

Although this paper focuses on improving experimental results by understanding zebrafishes’ behavior so that conditions can be improved,  it also highlights that current conditions in most lab settings do not meet even the basic social needs of zebrafishes. This is information that advocates can use to advocate on behalf of zebrafishes and other animals in laboratories. Given the vast numbers of zebrafish used in labs, and the range of invasive experiments being conducted on them, it is clear that this is a major animal welfare problem for this sentient, highly social species.