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Advice & welfare

What do Fish Want? Environmental Enrichment for Companion Fish

When looking out for the welfare of our pets, there are two key questions we need to ask ourselves: Are they healthy? And do they have what they want? As (sadly) we are not able to communicate with animals verbally, we need to carefully observe and understand their body language.

Animal welfare scientists can investigate an animal’s emotional state by seeing what’s going on inside and outside of their body and how they behave in their environment. The environment in which we keep our animals has a large impact on their emotional state. There are numerous toys, food items, activities, learning and exercise opportunities we give our pets to enrich their lives. Pet fish should be no exception to this. A growing body of evidence has revealed to us that fish can feel and behave and think in very complex ways (see previous animals voice article for more information). We know now that keeping a goldfish in a small, barren ‘fish bowl’ would be like keeping your cat in a cupboard. Providing our fish with opportunities in their environment to perform natural behaviours, such as foraging for food, playing, exploring and socially communicating, may produce positive emotions and help to give your fish a ‘good life’. One way to do this is by providing environmental enrichment.

Environmental enrichment involves any deliberate addition of complexity to the animal’s environment, such as structures i.e. plants and gravel, music, novel food items and introducing different fish species. The difficulty lies in determining what type and how much environmental enrichment fish want. For starters we need to make sure any potentially enriching item is relevant to the species’ biology and individual preferences. For example, some fish may prefer to hide, whereas others may prefer to swim in a current of water. Understanding our fishy friend’s sensory capabilities can help us to make the best decisions for them. Our choices, although coming from the best intentions, can sometimes be misguided. For example, red appears to be a very popular colour for dog toys, however knowing that dogs colour vision resembles that of human red-green colour blindness, a blue ball in the green grass may be a lot easier for dogs to locate than a red ball in the green grass. As our knowledge of the biology and intellectual abilities of animals expands, so should the way we care for them. We know that fish are sensitive to vibrations and therefore noises from tank equipment, slammed doors, and visitors, could be a potential source of stress for the fish. Playing classical music to fish could be beneficial, as the background noise of the music drowns out any sudden noises, which may scare the fish. One study showed that playing classical music through a mp3 player for four hours a day, significantly reduced stress in zebrafish.

It is also important to consider the social environment of your fish. For fish that group together for social reasons (i.e. shoaling species), such as, neon tetras, white cloud mountain minnows, and zebrafish, it can be very distressing to be housed in a tank on their own. Carefully choosing species to house together in a tank, can be socially enriching for some species of fish. For example, Angelfish added to a mixed group of white cloud mountain minnows, neon tetras, and tiger barbs reduced aggressive behaviours amongst the group. It is also important to consider the size of a group of fish and how they use the different types of enrichment in their tank, such as plants and hides. Depending on the species, if there are too few structures for the number of fish in the tank, there may be an increase in aggression due to competition for shelter and/or defending territories. Therefore, always make sure there is enough structural enrichment to keep everyone happy, without overcrowding the tank. A good rule of thumb is to keep approximately 50% of the tank floor covered, depending on the type of object.

Another approach in deciphering what animals want most is to offer them with a choice and see what they go for. Scientists can design experiments to ask animals to show us what they prefer by “voting with their feet” (or fins). For example one study found that when sticklebacks are presented with a choice between an open area of their tank and a shaded area with a cover on top of the tank, they preferred the area with shade. Sticklebacks also prefer areas with artificial plants to open areas. Their preference for shaded areas in their tank may be related to their species’ evolution as prey for birds and therefore feel more protected by above tank shade.

Another way to understand what animals want, is by seeing if they will “work hard” for something they want. One study found that goldfish will swim against a strong water current to access areas of their tank with plants, which shows that they have a preference for planted areas compared to bare areas of the tank. Interestingly, it didn’t matter to the goldfish if the plants were real or artificial. Therefore, goldfish will appreciate either type of plant enrichment you keep in their tanks. We know from interacting with our pets, every animal has their own unique personality and preferences. This is no different for fish. One study found that Nile tilapia fish have individual preferences for different size of substrate on the bottom of their tanks. Therefore, what one fish wants may not satisfy another. We need to continually pay attention to our fish’s behaviour and what they’re telling us with their body language. Environmental enrichment needs to be carefully chosen based on the species and individual preference, to keep our fishy friends happy and healthy.


Barcellos, H.A., Koakoski, G., Chaulet, F., 2018. The effects of auditory enrichment on zebrafish behavior and physiology 1–17. https://doi.org/10.7717/peerj.5162

Jones, N.A.R., Spence, R., Jones, F.A.M., 2019. Shade as enrichment : testing preferences for shelter in two model fish species. https://doi.org/10.1111/jfb.14129

Maia, C.M., Volpato, G.L., 2018. Individuality matters for substrate-size preference in the Nile tilapia juveniles. J. Appl. Anim. Welf. Sci. 21, 316–324. https://doi.org/10.1080/10888705.2017.1423229

Siniscalchi, M., Ingeo, S., Fornelli, S., Quaranta, A., 2017. Are dogs red – green colour blind? R. Soc. Open Sci. 4, 1–11.

Sloman, K.A., Baldwin, L., McMahon, S., Snellgrove, D., 2011. The effects of mixed-species assemblage on the behaviour and welfare of fish held in home aquaria. Appl. Anim. Behav. Sci. 135, 160–168. https://doi.org/10.1016/j.applanim.2011.08.008

Zhang, Z., Bai, Q., Xu, X., Guo, H., Zhang, X., 2020. Effects of environmental enrichment on the welfare of juvenile black rockfish Sebastes schlegelii: Growth, behavior and physiology. Aquaculture 518. https://doi.org/10.1016/j.aquaculture.2019.734782

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