I can tell you what I & others get on Chesapeake for the going rate on fish quest fishes, and maybe it will help ya figure out a Siege appropriate price range for fish quest fishes.
These are normally on deeds of 10 or 20 fishes per type.
Shallow and deep water quest fishes all go for about same price.
Dungeon fishes go for more.
Crabs and lobsters go for even more gp, cuz they a pain in arse to fetch up.
My fish quest fishes over there, across the board shallow deep,
on deeds of 10s sell for 50k.
*some will sell em for 40k for 10's* some will sell em for even more *spits* like Luna.

And usually 10 deeded up fish quest fishes are often more found than the 20's on deeds. Now the Luna mallers will sell em on 100s deed, or 500,000 but that is same as our 10s for 50k in price for shallow and deep anyhow.
Dungeon fish quest fish types, 60k + per 10 deed.
Lobsters and crabs WHEN ONE FINDS a vendor keeping those stocked,
5 on a deed 40k + & 10 on a deed 80k+ some lobster types crabs, harder to get even 10 of at all, go for more natch.
While that may not be appropo for prices HERE,
maybe it can give ya a guideline, for Siege fishquest fishes, at least.
So basically 5k a fish or 6k a fish quest fish, over there, depending on fish type, ie dungeon ones more, deeded up in 10s or 20s or 100s.
Lobsters crabs, R MORE.
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I think when I did sell some [HERE], it was 1k or 2k a fish, on deeds of 10s, 10k for 10 or 20k for 20 depending on type etc.
I always had some singles for sale too, for the fisher that gets 1 fry short of a happy meal of their needing 10 or 20 to complete quests and only got 9 or 19 of same stupid fish type.

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Anyhow those are the prices we /I net over there, on Chesapeake, for fish quest fishes on deeds and so maybe this will help ya for figuring out,
[Siege appropo.] prices from plain ol' pumpkinseed fish on up to, orc bass tormented pikes etc. from dungeon and crab$/lobster$, on deeds.
TMI I know, lol, just tryin' to help.