How many fish can you keep in a fish bowl. | |
There are several things to consider in deciding how many fish you can keep in an aquarium or fish bowl: surface area, water movement, filters, fish conflicts, and how experienced you are.
Surface area, water movement, oxygen and carbon dioxideThe water in your aquarium or fish bowl absorbs gases from, and releases gases into, the atmosphere at the surface, where the water and the air meet. We often think the fish need oxygen, but aquarium books tell us that getting rid of carbon dioxide is actually more important.Calculating Surface AreaTo calculate the surface area measure the length and the width of the area where the air touches the water, and multiply to get the surface area. If the sides of your aquarium are straight up and down just measure the length and width of the top of the aquarium. If you have a barrel type bowl you measure the length and width at the water line.If the surface area is a circle, measure the length across and divide by two to get the radius. Square the radius, and multiply by pi, 3.14. And, you thought you would never use the math you learned in school. Perhaps an example will jog your memory. If the surface area is a circle, six inches across, then divide by two, that is three inches. Now multiply the three inches by itself, that is nine and multiply by pi, 3.14, you get about 28 inches. Changing the Water Level and Surface AreaIn many bowls and jars you can frequently increase the surface area by lowering the water level. This gives the fish less room to swim, but increases gas exchange. This is a good idea if the fish are crowded. Room to swim is not as important as oxygen, and getting rid of excess carbon dioxide.Sometimes you can increase the surface area by raising the water level, if you do not have a cover make sure they can not jump out. For small fish I try to leave two inches. Water Movement and Gas ExchangeWater movement greatly increases the exchange of gases. Both air stones, and filters keep the water moving. Many times this is done by pumping air down into the aquarium and letting it bubble up to the surface. The bubbles do not force much oxygen into the water, it is the water movement at the surface that facilitates gas exchange. So a water pump is just about as effective in increasing oxygen content, and getting rid of carbon dioxide as an air pump, assuming that both move the same amount of water.Minimum of 3 Inches for Small MinnowsA small fish the size of an adult guppy, neon tetra, or zebra danio, say about an inch and a half in length, should have at least three square inches, 19 square centimeters, a fish, if there is no water movement. You can double the number of fish if there is water movement.A typical 10 gallon tank is ten inches, 25 centimeters, by 20 inches, 50 centimeters. This is a total of 200 square inches, 1250 square centimeters. It can hold 66 full grown guppies without water movement, or twice that, 132, with water movement. If I keep the water line at about three inches below the rim, the surface area on my two gallon bowls is about nine inches by six inches, or 54 inches. So theoretically one could keep about eighteen full grown guppies in a bowl without water movement. But I do not recommend that. My source for this is the Innes book, Exotic Aquarium Fishes, which for many years, perhaps decades,was the Bible of tropical fish keeping. Innes was the dean of the hobby. His importance is illustrated by the fact that the scientific name of the Neon Tetra is named after him. I have followed the advice of this book for decades, so I am speaking on the basis of my considerable experience with bowls as well as his much greater authority. These are maximum numbers, both Innes and I suggest that you double or triple the amount of surface area per fish for growth and better health. Furthermore, if you are using a filter, air stone, or other method to keep the water moving I would suggest that you avoid having more fish than can survive without water movement. That way if the electricity goes out, or a pump breaks the fish will still survive. Breeding a Special ChallengeThere is a big exception where you may want to have the maximum number of fish. This is when the fish are breeding and you are trying to raise a large number of fry. Even in this case, however, you might want to get rid of the excess fish so the others will grow faster.Speculation on Water Movement and Gas ExchangeFinally I would like to share some of my speculation on water movement, air stones and filters. The aquarium hobby started and existed for a considerable time before filters and water movement became the norm. One of the reasons they introduced water movement was to get oxygen down to the bottom of deep tanks.If you have a bowl or a relatively shallow tank this is not as much of a problem. Oxygen easily diffuses down into the tank. If the surface layer of the tank water is saturated with oxygen then at the surface the water maybe releasing about as much oxygen into the air as it is absorbing. It will be roughly in equilibrium. But if water from lower in the tank is constantly being brought to the surface it will not be so saturated with oxygen so it will absorb much more oxygen than it gives off. This maybe the reason that moving water increases the exchange of gases. What this suggests is that for very shallow bowls and tanks, perhaps where the water is just five inches deep or so water movement may not change the gas exchange. I do not know I am just speculating. This may not be particularly relevant because in my two gallon bowls the water is two inches deep. On the other hand I do have a tank where it is only three and a half inches deep. At any rate, if you are keeping bowls do not be bullied into using an air stone or filter. Remember these were invented to take care of problems that were specific to much larger aquariums. Other Pages On Bowls On This Site
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