Fish is one of those tricky English words that is used as both a subject and a verb. One definition of fish taken from the American Heritage Dictionary is:
Any of numerous cold-blooded aquatic vertebrates of the superclass Pisces, characteristically having fins, gills, and a streamlined body.
This definition illustrates the usage of the word fish as a noun. A sentence containing this usage of the word is as follows:
I like to eat fish.
A definition of the word fish when used as a verb, according to the same source is:
To catch or try to catch fish.
An example of this usage of fish as a verb is:
I love to fish.
Sometimes, the word fish is also used as an idiom or figure of speech. Examples of that usage taken from the same source are:
Like a fish out of water
Other fish to fry
Fish or cut bait
For absolute best usage of the word fish one must consider the context of the entire phrase and the intended meaning of the sentence or statement. In the first example sentence, the message was intended to convey a preference for the animal as food. In the second example, the message was meant to convey the enjoyment of the activity or sport of fishing. In the third examples, the meanings are more complex. Each instance given tries to convey a different meaning and uses the word fish to express specific emotions.
In the first instance, the intent is to state that the person making the statement feels uncomfortable, much like a fish would feel if it were kept out of the water. The second instance conveys that a person has many actions requiring their attention and the implication is that the current happening must take a backseat to it. In the third statement, the person is suggesting that they must act or give up.