Mustard

In The Ocean, a bulbous yellow pufferfish called Mustard is a Secret catch, and it pays far better than its looks suggest. It takes Seaweed as bait, appears in Rain during Summer, and can be caught at any time of day.

It weighs between 1 kg and 8.4 kg, averaging 2.5 kg, and that maximum ranks 479th of 663 fish with a documented maximum. The price is the surprise: at C$4,750 per kg, an average fish is worth C$11,875, 115th of the 742 documented fish by average value, and gives 7,000 base XP. Few small fish pay this much.

Ancient Orca and Moby are the other Secret fish documented in the same waters. Mustard is the light one of the group on paper, so its price does not depend on landing something huge, and that makes the payout easier to count on.

My advice is to go for it whenever it rains in summer and you have Seaweed. The setup is cheap, the payout is strong and the XP is high for a fish this small. It is a good return for the effort in The Ocean, and a good reason to keep Seaweed in your bag as the season changes.