People get compared to all kinds of animals. Sometimes it is complimentary, and sometimes not. In teenspeak, a language which I hear a lot of but am not fluent in (it is just too easy to make a mistake and break into ’80s teenspeak, which is totally different, and makes me seem old), it is good to be a beast at something. A fox may be intended as a complement, if you are a woman in a bar, or derogatory, if you are King Herod. A skunk is always bad. (And why do they say someone is drunk as a skunk? Skunks are far less likely to get drunk than hummingbirds.) So if you are compared to a mammal, there is at least a chance that you are not being insulted.
However, if you are compared to seafood, it is always bad. You can be a shrimp, or a whale (which is seafood in a few countries), and neither is good. It is not good to be crabby, or to carp about things, or to clam up. If you flounder around that is not good, and if you engage in fishy activities, that is worse.