Catch and Release Fishing Best Practices

This might be a novice question, but how long do you struggle with a hook before just clipping and leaving the hook there?
I was told that fish emit an enzyme that will dissolve hooks over time - is that true?

Compa's link was broken (it is 7 years old). This looks to be a functioning link: http://www.mnr.gov.on.ca/stdprodconsume/groups/lr/@mnr/@letsfish/documents/document/228125.pdf

This might be a novice question, but how long do you struggle with a hook before just clipping and leaving the hook there?
I was told that fish emit an enzyme that will dissolve hooks over time - is that true?

Yes, especially if you use "cheap" hooks.