Updated: Nov 7
Many species of freshwater, brackish and marine pufferfish bury themselves into the substrate. This behaviour is known as "wallowing" and is one of the reasons some pufferfish are so much fun to watch and keep.
They may do this for several reasons, such as to hunt, to avoid the detection of bigger predators (who might eat them) or simply just to rest.
Some pufferfish bury themselves in order to camouflage while they hunt. They may only partially bury themselves, or they may almost completely conceal themselves with only their eyes and mouth protruding from the substrate.
Many crustaceans travel across the ground and many other fish closely inspect the substrate looking for potential food. These are the targets for many a sneaky and hungry pufferfish. The pufferfish lays in wait for any unsuspecting prey to swim close enough and then emerges from the substrate to launch a surprise attack, with surprising speed and aim. Waiting for the prey to come to you is a very efficient hunting technique because it demands such little psychical expenditure.
Choosing a substrate for a wallowing pufferfish
Special attention should always be given to selecting the right substrate for your wallowing pufferfish.
Pufferfish dig into the substrate by nose-diving it and using their powerful tails to push their whole body forward into it. If the substrate is too hard or abrasive then this may cause scrapes and scratches which could be painful for the fish and predispose it to bacterial and/or fungal infections.
Fungal and bacterial organisms will take full advantage of even minor abrasions, so it is important that we do everything we can to prevent such injuries.
As a general rule, fine sand is the best option for any wallowing species of pufferfish. The softer the sand is, the better for the fish. We strongly recommend UniPac Silver Sand (as shown in the video) or JBL Sansibar, because they are both soft enough for wallowing pufferfish without the risk of injury.
Play sand or Pool Filter sand can also be used, providing that it is fine enough and doesn't contain any potentially harmful chemicals.
A fine substrate is also easier to clean than a course one because it retains less organic waste. In fact, because the grains of fine sand sit together so tightly, the waste stays on top of the substrate making it easier to clean, instead of allowing it to fall into the gaps between individual pieces of gravel where it can then rot down and contribute to poor water quality.
How deep should the substrate be?
The depth of the sand should always at least match the depth of the fish's body. It is recommended to start as shallow as possible and gradually increase the depth as the fish grows.
What about anaerobic pockets?
The fish will disturb the substrate on a regular basis by moving from place to place within the sand, but it is recommended that the keeper regularly stirs up the substrate to stop the sand from ‘compacting’ and to prevent the build-up of anaerobic bacterial populations.
Bare-bottom and "wallowing bowls"
Some keepers may choose a bare-bottomed aquarium because they feel it is easier to keep clean, or may find it more visually appealing for themselves, but the primary concern should always be the welfare of the pufferfish. Bare-Bottom tanks deny a wallower the opportunity to express its natural behaviour and depriving an animal of crucial enrichment should always be considered unethical.
What about a bare-bottom tank with a bowl/tray filled with sand?
This initially seems like a good compromise, but your pufferfish may choose it's wallowing location based on several different factors, such as the light or shade in the area, how secure that area feels at certain times of the day or the strength/direction of the flow. A wallowing pufferfish should always have the option to wallow in as many places as possible and shouldn't be confined to a mere bowl or tray.
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