When we built an aquarium, we talked about the territory that the fish took for their own, and that different fish feed at different levels of the aquarium. We decided that we should have some fish from each group of feeding levels: top, center, and bottom. The reason is that it is good for all the fish to have a balanced aquarium. The aquarium is an ecosystem, each part of it being dependent on other parts. To keep the water in correct balance, we have to be certain that all the food we give them is eaten, and the only way to do that is to feed the correct amount, and to have fish that eat in different places.

This project might be a trick! The outline suggests that we have an aquarium with goldfish, sunfish, and catfish in it. Do any of you know what is wrong with that idea?

(1) Goldfish are fresh-water fish that do best in water at a temperature of 65o to 72o. They are very aggressive, have large, flexible mouths, and will eat anything they can get into their mouths. They don't care what level the food is; they will eat it. They even eat from the floor of the aquarium. They will nibble at your fingers if you put them into the water at the top.

(2) Catfish, are fresh-water fish also. The kind you find in rivers and lakes do well in cool water. They are very aggressive, have large mouths, and will also eat anything. The kind of catfish you can keep in an aquarium, however, are tropical catfish. They are small, stay in the bottom of the aquarium, and do good jobs of keeping the aquarium clean by eating particles of food that fall to the floor. Their mouths are on the underside of their bodies, and they have whiskers to seek out particles of food. They require water heated to between 73o and 78o. If they were in an aquarium with goldfish, the goldfish would surely kill them, if the cool water didn't kill them first. Further, since goldfish eat at every level of the aquarium, they probably wouldn't allow enough food to fall to the floor to feed the catfish.

(3) Sunfish are salt-water fish and cannot live in fresh water. They are also not compatible with goldfish or catfish. They do feed at the top of the aquarium. Their bodies glint in the light as they race to the surface for their food. Their mouths are sort of on the topside of their bodies, and they would have difficulty eating from the floor.

It is quite interesting, and marvelous, that all animals seem to have the equipment required for their special feeding needs. There is one tropical fish that grows quite large, and its mouth opens rather like a telescope! When it reaches out for its food, it is a surprise to anybody who is watching, because one would never expect that. This fish can be three inches away from food, open and telescope its mouth, and grab that food!

The plecostomus we bought for our aquarium has a large, round mouth that looks like, and acts like, a suction cup. Its mouth is perfect for sticking to the side of the aquarium and sucking off the algae.

Similarly, birds have special beaks which gives them the ability to find and eat their particular foods. Humming- birds have long, narrow beaks for sucking nectar out of bell-shaped flowers. Woodpeckers have very strong, sharp beaks for pecking holes into wood and reaching in for the little insects and grubs that are inside. Spoon-bills have wide, flat beaks, with a structure on the end that is very much like a spoon, so they can walk through shallow water, and ladle up their food.

Understanding ecology begins when we realize that all organisms of the earth are dependent, to some extent, upon all other organisms. There is a theory that the earth and everything on it is one thing, and that everything needs everything else, including the earth itself, in order to survive. That is a very simple way of explaining the "Gaia" (pronounced "GUY-ya") theory.