I strongly advocate for re-releasing. Since you don't know the exact species, you don't know what it needs. Further, this isn't like a tank-bred fish - it's used to having the whole lake to swim around in. Confining to a tank seems unnecessary and restrictive. If it's omnivorous, it will be used to a varied diet of live food, which you won't necessarily be able to supply. You don't know how it will take to captivity, and I worry that you will be risking its wellbeing by attempting to make it do so.
You may have gathered, I am very against people taking catching animals in the wild.