Labyrinth fish such as bettas have the ability to breathe air from the surface. • plepraisaeng
DO is suspected (based on your observations). When testing for DO, we usually want a level of at least 6 mg/L, but 7 is ideal. P.R. Escobal (2000) states that dissolved oxygen should never fall below 5 mg/L, especially when medicating fish. Again, temperature plays a role as well as the size and species of fish you are working with. Larval fish with underdeveloped respiratory systems are very susceptible to low DO, while labyrinth fish (able to breathe air), certain catfish, and carp can handle very low levels, even less than 3 mg/L. Another factor to consider is the biological oxygen demand, the number of organisms competing for the available oxygen. One sign that your fish may be suffering from low DO is if it’s “piping” at the surface, or attempting to take in extra air (Jones 2012). If there
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These oxygen-starved fish are “piping” at the surface. • lapis2380
is not enough oxygen in the water, it may lead to anoxia, the absence or deficiency of oxygen reaching the fish’s tissues. Rapid breathing or very slow breathing can also be signs of respiratory distress. In aquariums where we have motor-driven filters with tight-fitting lids, DO can become greatly reduced and can lead to unsuitable aquatic conditions. Fenner (2008) suggests that an aquarist should design an aquarium to have a redundancy of aerators or circulation. He also mentions that in seriously oxygen-depleted systems, anaerobiosis can occur, and the telltale sign is a foul, rotten-egg odor with bubbles occasionally rising to the surface from stagnant areas of the aquarium. Don’t let your aquarium get to this point. Maintain proper water quality, perform frequent partial water changes, and
The Importance of Oxygen in Aquariums • 37