What would be like a standard breathing count? I’m sure it’s different with age, species, etc... but is there a standard breathing rate per second/minute?
Respiration rates vary between species, size of the fish as well as water temperature. That's why getting baseline readings on new fish is so important - if you buy a tang and the next day you count and it is breathing 70 beats per minute, but the following week it has gone to 90, you wouldn't notice that by just casually looking at it, but by know what the count was, you know there was an increase - and now you have advance notice of a impending issue.
I have a section on respiration rates in my upcoming fish disease book, but it includes graphs and tables that I can't paste in here. Here is the introductory text though:
A note on respiration rates
Aquarists are warned throughout this book about 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 fish of the size kept in smaller aquariums should breathe 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 later suspect a problem. Not having this baseline data is an issue for newly acquired fish, so using the information below may serve as a secondary reference.
Fish may exhibit a variety of respiration forms in addition to the actual 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.
Jay