Green Algae Chlorophyta

Green algae abound in nature and are distributed ail over the earth, although most species are found in freshwater. They reproduce mostly vegetatively but can also develop microscopic sexual organs resulting in minute spores. These spores are easily introduced into the aquarium with water, plants, or through the air.

In appearance greens vary greatly from unicellular forms which float freely in the water to multicellular filaments attached to stones or other plants. The unicellular forms may be so abundant as to color the water green or may be attached to plants, the aquarium glass, decorations, and the substrate. The filaments may produce dense tangles among the higher plants. Because their requirements resemble those of many higher plants, they are often common in the aquarium but do little harm unless present in very-large numbers. They produce oxygen as well as the higher plants.

The minute species can be very troublesome when they attach to the leaves of plants and decrease their food-making efficiency. They are usually firmly attached and cannot be easily removed. Since they attach mainly to the older leaves and to stems, seldom to young leaves, the infested leaves can be cut off and removed from the aquarium. Algal films on the glass can be removed by various types of aquarium scrapers and sponges.

Filamentous green algae are seldom a nuisance unless they are allowed to reproduce excessively. Unattached filaments should be removed from the aquarium regularly with a net. Most attached filaments are only a few centimeters long and do not interfere with the higher plants. Some look very attractive and can even serve as spawning media for fish.

Ventral view of the Chinese algae eater showing the mouth adapted for scraping off algae.

Anahaena sp., a blue-green alga.

Cladophora. a green alga. Photo by Frlckhinger

Tadpoles are efficient algae eaters and are easy to obtain. Photo by H Pfletschinger.

The occurrence of green algae in the aquarium is a sign that conditions are good for the development of higher plants and fish. If kept under control by regular mechanical cleaning of excess algae, they are often a positive addition to the tank. Some species are used as food by such fish as mollies, Chinese algae eaters, many species of barbs, and many of the South American armored cat-fishes.

Complete removal of green algae from the aquarium is very difficult unless chemicals are used. The fish mentioned above will help, as will snails. Most green algae are too hard for snails, however, which prefer to nibble on the more tender leaves of higher plants.

Another well known algae eater is the upside down catfish {Synodontis nigriventris). Photo by G.J.M. Tlmmerman.

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