What indicates that this is a definition clue

What are context clues? Context clues are hints that an author gives to help define a difficult or unusual word within a book. The clue may appear within the same sentence as the word to which it refers or it may follow in the next sentence.

Explanation: Context clues are hints that an author gives to help define a difficult or unusual word within a book.

d) the narrator even suggested that the white whale, moby d, was ubiquitous and present in every ocean at every moment.  

halibut, flounder, tuna, and trout are all fish. so your first answer is 1.) fish. and since fish is edible, your next answer would be 3). edible

to describe those fishes more thoroughly, some of those fishes live in fresh water, and some of the fishes live in salt water, and that is not a thing that they all have in common. the question is asking what is common with all of the fish, so answer choices 2). fresh water and 4). salt water are not right.