Marine Fish Respiration Rates

A means to objectively determine relative stress levels in fish


Aquarists are frequently advised to watch for rapid breathing in their fish as a symptom of potential problems, yet few know just what “rapid” is.  Obviously, fish kept in warmer water or those with gill disease will respire more rapidly.  Actively swimming fish respire faster than sedentary ones.  Less obvious is that larger fish respire more slowly and, in some cases, high ammonia levels will cause a fish to respire more slowly than normal.  While there is some difference between species, (Chinese algae eaters will breathe twice as fast as any other fish their size) most tropical marine fishes of the size kept in home aquariums should breath at a rate of between 70 and 120 gill beats per minute.  Relative respiration rate is the most important value – capturing the respiration rate of your fish when they are known to be healthy, gives you a baseline to compare to if you suspect a problem later on. 


Fish may exhibit a variety of respiration types in addition to the rate itself;


Mouth open respiration – may be a sign of gill disease or toxic compounds in the water.

Rapid shallow respiration – may be signs as above, or just a result of high activity level.

Coughing – a result of high levels of particulates in the water, or gill parasites.

Gasping at surface – usually seen in freshwater fish under low oxygen conditions.

Slow, deep respiration – may be normal, or a sign of ammonia toxicity.

Slow, shallow respiration – normal for most fishes.


There are few objective measures that aquarists can use to judge the overall health of their marine fishes.  In many cases, the aquarist must make a subjective evaluation based on the fish’s feeding response, fin condition and general activity.  Respiration rate is one of the easiest means to objectively measure fish health – as long as a normal rate can used for comparison. Apparently healthy Emperor angelfish will sometimes breath using just one operculum.  They can also “skip breath” – showing no gill movement for a few seconds.

Jay Hemdal