Enrichment for Goldfish

What keeps goldfish happy in their tank – and how do we know?

A goldfish swims in a tank with lots of artificial and real plants
Photo: The Gallery/Shutterstock

By Zazie Todd, PhD

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You’ve heard about the importance of enrichment for companion animals (like dogs) and for zoo animals, but what about goldfish? Fish are the third most popular pet - kept by 12.3 million households in the US - so it’s an important topic for animal welfare. Different types of fish might have different preferences. A new study by Miriam Sullivan (University of Western Australia) et al investigates.

Enrichment “is particularly important for goldfish and other pet fish for two main reasons,” Miriam Sullivan told me. “One, people tend to underestimate how smart fish are, which probably means they spend less time and effort on enrichment for their fish compared to other pets like cats and dogs.”

“And two, fish health is really closely connected to their environment. If fish are stressed out due to a poor environment (e.g. if they lack shelter or you didn’t clean out the tank!) then they become more susceptible to bacterial infections and other diseases.”

So how do we even know what goldfish want? One way is to use a motivational test – something that requires an effort, so you can objectively measure how much effort they will put in to get a particular resource. 

For example, an earlier study with Tilapia (Galhardo et al 2011) involved training the fish to touch and push a door with their snout to access different resources; increasingly bigger weights were added to the door to find out just how motivated they were. 

But this study tries a different method that needs no training – using successively greater currents to find out how hard goldfish will swim to access a resource. This method is especially appropriate for goldfish because domestication has affected their swimming ability. As a slow water fish, swimming against a current is hard work.

20 young Comet Goldfish (Carrassius auratus) took part. Fish were individually placed in the empty middle section of a special testing tank. On one side was a compartment with artificial plants, and on the other, a compartment with real plants. The plants were Bacopa and Ambulia, and the artificial versions were cut to size to match the real ones.  

Half of the fish had the real plants on the left side, and half on the right, in case of a left or right preference. And in fact 14 of the fish turned left first, but they did not spend extra time on the left overall. The fish preferred to spend time in a compartment with plants – real or artificial – and only spent 10% of the time in the empty part of the tank.

For the motivation test, fish were placed in a tank where they had to swim through a tunnel against a current to get to either real or artificial plants or empty space. If they went through the tunnel, the current was increased on successive occasions to see how hard they would swim. In between each trial they had a couple of days rest. 

11 of 19 goldfish swam against even the strongest current for all three options. Of the remaining 8 fish, 2 preferred the empty space, 3 preferred real plants, and 3 preferred either type of plant.

“The main implication for goldfish owners is that it doesn’t matter if you use fake plants,” says Dr. Sullivan. “This is good news because goldfish just love to destroy things, so it can be really hard to keep live plants alive.”

“The only caveat to this is that in some of my other thesis research, I found that goldfish owners tend to be newer owners who don’t always clean their tank or maintain good water quality. If you aren’t able or willing to keep your water super clean, then you should still use live plants because they help keep your water clean. But if you’ve got everything else right, relax and throw in some fake plants!”

Dr. Sullivan also suggests that you rotate enrichment items just like you would for other animals. 

Her other tip for happy fish? “Buy the biggest tank you can afford. My research and lots of other emerging research is starting to suggest that swimming is really important for fish behaviour and health.”

Which explains why most goldfish were willing to keep swimming to empty space, as well as to plants.

What kinds of enrichment do you provide for your fish?

Zazie Todd, PhD, is the award-winning author of Wag: The Science of Making Your Dog Happy and Purr: The Science of Making Your Cat Happy. She is the creator of the popular blog, Companion Animal Psychology, writes The Pawsitive Post premium newsletter, and also has a column at Psychology Today. Todd lives in Maple Ridge, BC, with her husband, one dog, and two cats. 

Useful links:

Galhardo, L., Almeida, O., & Oliveira, R. (2011). Measuring motivation in a cichlid fish: An adaptation of the push-door paradigm Applied Animal Behaviour Science, 130 (1-2), 60-70 DOI: 10.1016/j.applanim.2010.12.008  
Sullivan, M., Lawrence, C., & Blache, D. (2015). Why did the fish cross the tank? Objectively measuring the value of enrichment for captive fish Applied Animal Behaviour Science DOI: 10.1016/j.applanim.2015.10.011

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