imuya -> i-168_(kantai_collection) (イムヤ)
gouya -> i-58_(kantai_collection) (ゴーヤ)
shioi -> i-401_(kantai_collection) (しおい)
These characters use the nicknames to refer to themselves and they tell you in their introduction/secretary line to use the nickname too rather than the number.
hachi_(kantai_collection) -> i-8_(kantai_collection) (はち) (She has also lines asking you to call her Hacchan instead)
iku_(kantai_collection) -> i-19_(kantai_collection) (イク)
Same, but the nicknames are less distinct, so I guess they need the suffix?
In case it's needed, kana in parentheses are taken from their introduction lines.
maruyu_(kantai_collection) -> maru-yu_(kantai_collection)
I imagine she's more commonly known as "Maruyu" since that's the way it's spelt on the KanColle wikia.
kancolle -> kantai_collection
Abbreviation -> Full name
The abbreviation 艦これ is used pratically everywhere.