To condense 40 pages of biology in to a sentence..
" Low presser area reduces the presser on the water and the fishes swim bladder can not change as quick as the water presser so, they are bloated to the point that they are too uncomfortable eat, chase food, breed, etc" ...
Depending on the water temp and depth of the low, it could be up to 60-70 hours before there bladder and water presser balance out again..
HINT--- The deeper the water the less of this effect will be felt !!!!!!!!!!!!!!!!!!!!