Capitalisation of fish names depends on the context.
If you are talking about the name of a specific fish, for example a pet fish, you would capitalise (eg. "Bob" my goldfish)
If you are using the common name of a type of fish in a sentence, you do not need to capitalise (eg. I ate salmon/trout/sardines last night) unless it is the start of a sentence.
If you are using the scientific name, you capitalise the genus name but not the species name (eg. Salmo salar)
Yes you do.
Yes.
yes
They are proper names of direction.
Yes,names of the week are always capitalized.
Yes, in writing, you should capitalize the names of books.
no
No.
Types of fish are generally not capitalized.
Yes you do.
Yes you do.
Yes.
no you do not capitalize the names of trees
yes because you capitalize all names
Yes.
Yes.
Capitalize them