by David Schaeffer
Ever since there have been affordable home aquariums, there has been a demand for "mini" tanks that can still be used for fish. Desktop aquariums are inexpensive, readily available, and might seem like a great idea at first, but the realities of water quality management make them something not well-suited to the novice. Bigger really IS better when selecting a home for your fish.
For those of you with severe space limitations, or those who are ready to advance to something (just a bit) more complicated, there is good news: It can be done - you have to follow some rules, though.
Before I begin, let me say that the "micro-aquariums" with a volume of well under a quart that purport to need no filtration, etc., are cruelty to fish, pure and simple. No serious aquarist would ever use or recommend one, and for good reason. This is not the forum to discuss this in detail, so I'll leave it at that for now, but I don't want anyone to think I'm condoning anything like that with this column. A fish's health is ALWAYS of a higher priority than the entertainment or novelty value it provides. We'll get on with things just as soon as I climb off my soapbox…
To start with, the general principles of aquarium management apply to all tanks, be they large or small. In a small tank, waste levels can rise and oxygen levels drop to dangerous levels in a matter of hours instead of days. What to do? Well, one thing you want to do is make sure you have good filtration. A foam filter will do nicely and has the advantages of easy maintenance and affordability. Partial water changes are, as always, a must, and not overstocking the tank is important. Now is also a good time for me to mention the Unsung Hero of the Mini Aquarium: the pond snail. Make sure you have some of these guys in your tank. They'll be a tremendous help picking off any leftover food.
There are a large number of truly tiny fish out there, but many of them take some searching out. If your local pet shop can't order any of the species mentioned in this column, a local aquarium club should be able to help you out.
For my money, the King of the Mini Aquarium has to be the least killifish, Heterandria formosa. A dwarf livebearer (not a killifish) native to the southeastern United States, males of this species seldom reach an inch in length. A one-gallon tank or jar can comfortably house a pair, but I'd recommend plenty of plants, as they can be a bit shy. A two-gallon bowl allows you to keep two pairs and observe more varied behavior. Dust-fine dried foods are eagerly eaten, but make sure plenty of vegetable matter is given. An abundance of plant growth, besides making them feel at home, also provides refuge for the microorganisms that fry will appreciate. Young H. formosa are usually not bothered by adults and most times are too large for the adults to eat. Normal room temperatures are just fine for keeping and breeding and, as an additional benefit, they only give birth to one or two young at a time, over a period of a few days to a few weeks. Unlike their cousins, guppies, mollies, platys and swordtails, the least killifish won't overwhelm your biological filter by dropping 50 youngsters at a time.
While there are some other fish that would do well in something as small as one gallon of water, H. formosa is the only one hardy and inexpensive enough to recommend to virtually any hobbyist regardless of experience level.
When you are talking about aquariums of two gallons or better, your options expand dramatically. The two-gallon glass or plastic drum bowls intended for goldfish make terrific homes for some of the smaller killifish, for H. formosa, or for the Everglades pygmy sunfish.
I was able to keep a pair of Aphyosemion gabunense for an extended period of time in a simple two-gallon drum bowl with a large clump of Java moss and an airstone. Fifty percent of the water was changed weekly, and there was no gravel. With only the pair of killies and no overfeeding, maintenance was a snap. As a matter of fact, from time to time I had to net youngsters out of the bowl. I would recommend a small sponge filter just to be safe, and the plants are MANDATORY - the female needs a place to hide if the male gets too boisterous. Not all killies will work in this situation, so ask your local aquarium club members for tips.
If you can provide the live foods they usually need, a pair of pygmy sunfish will make a striking display as well, especially when the male is in his smoky black and electric-blue spawning garb. One other note - if using a drum bowl, resist the temptation to fill it too high. A bit over half to three-quarters of the way full gives the fish more surface area for gas exchange. To sum up, for a bowl you'll need some source of aeration, some kind of bushy plants for cover (Java moss is my favorite, but Najas, Hydrilla, Nitella, Chara, and anything else that allows fish to hide will work), some snails, and some tubing to siphon the bottom when it's time for those regular partial water changes. A cover of some sort is advisable.
Once you step up to the 2.5-gallon glass aquarium, the rules and possibilities are the same as for any aquarium, but remember to UNDERSTOCK. If things go south water-quality-wise in a tank that small, it happens fast, so don't tempt fate. Good choices for the 2.5-gallon tank include Endler's livebearer, wild guppies, a wide variety of small to medium killies including seudepiplatys annulatus and Leptolucania ommata, and a few dwarf croaking or sparkling gouramies, Trichopsis pumilus.
There are other fish and other scenarios that work, but what I've mentioned in this article is as close to foolproof as you can get. As always, get your feet wet with something easier before moving on to a more challenging fish or more complicated setup.