Tuna

The  is one of sixteen(16) different fish that can be caught, and either processed for cooking or sold to the Lighthouse Keeper. It's thought to be a relatively mid-tier fish, thus the difficulty in catching it is moderate.

Fishing
The odds of catching a fish are affected primarily by the other fish in the area at that time. More competition means your chance of catching a particular fish over another is lowered. Here is a table of this fish's preferences by the bait used, the place you choose to fish, where you choose to cast, the rod you use, and the time of day. You have a slightly higher chance of catching a Tuna using a good rod than an excellent rod, but often it will be of lower quality.