The Multispecies Aquarium Community

You never know what you’ll find when you open the refrigerator in Pacific Science Center’s Animal Care room. Take for instance this past week. Inside the 40°F refrigerator, slowly swimming around in a plastic container were Flopsy, Mopsy and Peter Cottongills, our resident Axolotls. What were they doing there?


For almost a year our trio of Mexican axolotls (Ambystoma mexicanum) has lived in freshwater aquatic bliss only having to share their tank with a few docile guppies. Now the neighborhood has changed. Animal Care has recently acquired some African dwarf frogs (Hymenochirus boettgeri). What could be a better home for the dwarf frogs than the Axolotl tank?

Multispecies aquaria can be challenging to create. We must consider the temperature, salinity and pH of the water that the different species need. Are their environments compatible? With a little research we learned that the freshwater requirements of axolotls, frogs and guppies are pretty much the same.


Next we wondered: Can the African dwarf frogs peacefully coexist with moderately aggressive axolotls? Or should a separate apartment be created for the smaller animals? Considering that the tiny and aptly named African dwarf frogs are just about bite-sized for an axolotl, we elected not to test our luck. We reconfigured the aquarium with a pane of Plexiglas dividing a small portion of the tank for the frogs.

In addition to making spatial arrangements for our new dwarf frog residents we also gave the tank a full clean. As a regular readers may recall, keeping a clean aquarium for axolotls has been difficult. In the meantime, Flopsy, Mopsy and Peter Cottongills took up temporary residence inside the refrigerator, which gave a little shock to Animal Caretakers dropping off their lunches first thing in the morning.

The aquarium has since been put back together and our aquatic animals appear to be happy and healthy. Come check out our new multispecies aquarium on view for the public.

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Inside the Tide Pool

Behind the painted wall of the Puget Sound Saltwater Tide Pool touch tank, a pump, chiller and two large vats work nonstop to circulate, cool, and filter the water. Just like most home aquarists, we do a partial water change each week. And like many, we back-flush our pipes and filter media to keep them clean and operational.




Sometimes routine care is not enough, and we need to do some special maintenance to keep our system working its best. After the September full clean, the tide pool looked great, but changing out so much sand and water had diminished our population of beneficial bacteria.

To help foster new beneficials, we never clean both the touch tank area and our filtration vats at the same time; we try to leave at least six weeks between the two jobs. This keeps a reservoir of good bacteria, most of them lodged in floating Bio Balls that provide lots of surface area for helpful organisms to grow.



Unfortunately, the same surface area acts as a trap for lint, dust, hair, glitter, undigested food and sloughed material from the sea creatures, and a host of other unwanted debris. This waste drifts to the bottom of the vat, clogs the manifold that draws water into the pump, and therefore slows down water circulation. So after the six weeks elapsed, we knew the vat was ready for a little cleaning.

First the Bio Balls were lifted out of the vat to allow access to the water below. Note that the water in the touch tank area was perfectly clean looking, but the vat had accumulated enough solids to make it hard to see the bottom.






Next, the cloudy water, along with precipitated solids, was siphoned out of the vat. The last bit had to be cleaned out by hand.


At this point we could reach the manifold, which desperately needed cleaning. The manifold’s job is to allow water into the pump without allowing solids to get sucked in and possibly damage the machinery. The screen material that should let water through had become filled with particles and was causing the water to slow down. A good, hard rinse dislodged the gunk and the manifold was back in business.



We never use anything but water, salt and elbow grease to clean objects in the tide pool; soap and other cleaners can be deadly to the animals.


Putting the system back together is always easier than taking it apart. The manifold and Bio Balls were returned to the vat. Then we added enough synthetic sea water to make up for what we siphoned out. Through the rest of the day, we monitored the temperature, salinity, and circulation. Everything looked good, and by the end of the day, our system was back in business.



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Axolotl Challenge

The paradox of caring for Mexican axolotls is that they need extremely clean water, but their eating habits are extravagantly messy – creating anxiety for our Animal Caretakers at Pacific Science Center. Fortunately, our creative staff have figured out a way to keep our amphibians’ habitat clean and healthy.



Axolotls are native to two lakes in Mexico; their habitat is very threatened in the wild. They do well in captivity and are fascinating animals for those who are willing to work hard to keep water quality high.

Unfortunately axolotls are very messy eaters. They dive at food, eating as much as they can and letting the leftovers scatter through the water. In an aquarium habitat, this leads to loss of water quality and can make the animals fall ill.


Pacific Science Center's animal care team takes this problem seriously - but they also like to have fun. Adrian and Nancy have been working on some feeding schemes to help keep the mess to a confined area. Here are Nancy's drawings.

And here is the feeding chamber.


The animals can learn to go in, eat, and come out again safely. The chamber can then be pulled back out, taking most (but never 100%) of the leftover food with it, and leaving the water relatively clean.
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