How can lake trout adjust to changes in pH?

Supposing the lake is salt water, the trout in the lake would be considered to be an ';osmoregulator.'; An osmoregulator is an organism that controls its internal osmolarity independent of that of its environment. What this means is, they can either expel a lot or a little of the salts (which can change the pH levels in the trout) it takes in from the mouth as urine. Trout live in water more concentrated than body fluids, therefore they tend to lose water and gain salts. Typically, they urinate smaller amounts, and their urine is slightly less concentrated than body fluids. So to answer your question directly: they can adjust to changes in pH by either increasing or decreasing the amount of salt contents they contain and excrete as urine (since they are osmoregulators).

Hope this helps.

-ChrisSmith83