It sounds like something a bureaucrat wrote. Say "to catch" instead.
She is catching up with her homework.The horse was catching up with the rest of the herd.
There is no conjunction in the sentence, "Catching fish is one of the oldest pastimes."
Yes, fish in this sentence is a noun.In the example sentence, the noun fish is part of the noun phrase 'catching fish', which is the subject of the sentence.
In the sentence, "Catching fish is one of the oldest pastimes.":the preposition = of;the verb = is (a linking verb).There is no conjunction or adverb in the sentence.
An entire sentence can't be a conjunction, and there is no conjunction in that sentence.
If the sentence is a question then it does.
The cat focused on catching its dinner.
In this sentence, "catching fish" is a gerund: a verb that is doing the job of a noun. "Catching fish" is the subject of the verb "is".
Near Christmas the Police were doing spot check on motorists, testing them to ensure they had not been drinking.
An example sentence is: The three fishermen spent all morning in the boat catching fish.
As a question, it can be a sentence, like: A sentence can have one word, and as a question then it can be a sentence: Who?
I think I am catching a cold.Do you think you are catching a cold?