Some people like a petty or suji between 150mm and 180 or 210mm. They are usually somewhat flexible, thin and take a very fine edge. Others prefer a Deba, especially if they are breaking down the whole fish, removing heads, etc. Using a Deba is a different type of skill set though since it's a thick, heavy knife, but can still handle delicate jobs, too.
I picked up a Tojiro 155mm Stainless Steel Deba; it's thinner at the spine that most Debas and is single bevel, but not hollow ground on the back for inshore fish, but I haven't gone inshore fishing since I got it
It did work very well on beheading Rainbow Trout this year though and cleaning them!http://www.chefknivestogo.com/tojiro1.html
Fujiwara Stainless or Carbon 150mm petty would probably be a good one to try to see if you like that way it works. Or get an inexpensive Deba (Tanaka and Tojiro 165mm are under $100) and see how you like that. If you are just filleting/skinning, I would look at the petty or short suji type knives.