Yep, now that you’ve posted the question (although I still don’t se any italicized text), we can help you. Looks like the answerer above me knows there stuff so I won’t add any more.

A. Verb
B. Adjective
C. Noun
D. Pronoun

Thank you for updating your question. Now it can be answered.

“catching is” verb phrase separated by the noun “fish”

“oldest” is the adjective.

If you were to take out the word “And” from your final example you would have a complete sentence.

Large fish swim swiftly in the sea.

“large” is your adjective, “fish” is your noun, “swim” is your verb, “swiftly” is your adverb, and “in the sea” is a prepositional phrase describing the fish’s place in the noun “the sea.”

A. Conjunction
B. Pronoun
C. Preposition
D. Linking verb