The speaker meant to say “a bitter pill to swallow” (an unwanted or unpleasant situation that someone is forced to accept) but apparently had fish on his mind. This is a mashup of “a bitter pill to swallow” and “big fish in a small pond” (a person who is important in a limited arena). Fish do get swallowed up by other fish and they do swallow hooks, so these pictures might have been on the speaker’s mind as well. Or maybe he was thinking of the classic movie, “Big Fish”. A shout out to Sandor Kovacs for hearing this one and Mike Kovacs for reporting (and saying) it.