Hello there!
Probability helps determine the chance that something will occur.
Hope this helps, and have a nice day.
Most fish (especially the "Bony fish") achieve neutral buoyancy through a sac called the swim bladder in there body of which is filled with air, not much but it'a just enough to keep then a float. The fish can control this organ, and using that they can fill or release air to allow them to rise or sink.
Cartilaginous fish however, do not have a swim bladder.
hope this helps :)
Umm. can you add a picture of it??