Continuity mistake: When Mickey is about to put the hook through the fish, you can see in a long shot that Mickey's hand is above the fish, holding the hook. However, in a close-up of the fish, Mickey's hand is nowhere to be seen.
Continuity mistake: When Pluto pulls the mussel on his tail like a yo-yo, the mussel gets stuck in his mouth and you can see there is nothing on the sand dune behind him. In the next shot, the sand dune now has grass on it.
Continuity mistake: Mickey Mouse is wearing a hat and fishing when a seagull lands atop his hat. The seagull is facing Mickey's right but when Mickey looks down to see their shadows, the shadow of the seagull shows him facing Mickey's left.