Observe fish in an aquarium. They open and close their mouths and the gill-slits (or the operculum which covers the gill-slits) behind their eyes also open and close.
Are the timings of the opening and closing of the mouth and gill-slits coordinated in some manner?
- ✅ Answer: Yes. During breathing, fishes open and close their mouth & gill slits in a coordinated manner and timing.
Count the number of times the fish opens and closes its mouth in a minute.
- ✅ Answer: It is varied based on the type and size of fish. For example, goldfish can breathe up to 100 or more times per minute.
Compare this to the number of times you breathe in and out in a minute.
- ✅ Answer: The amount of dissolved O2 is lower than that in the air. So, the rate of breathing in fishes is faster than that in terrestrial organisms. The normal respiratory rate of an adult human is 12-16 times/minute.