finegrain -
Actually ling cod don't have a closed air bladder so they can handle pressure changes well - they can be caught at great depth and still be successfully release - just like salmon.

Rockfish however have a closed bladder and will suffer from the "bends" - the sudden reduced pressure causing the air bladder to expand causing damage and death when brought from the depths.

I find that lings fight well when caught on appropriate size tackle. A 10# ling on steelhead size tackle or a 7/8 weight fly rod give a good account of themselves.

Tight lines
S malma