On Earthen Ring:
Before 1.11, ten eels would sell for 12 gold and ten oils for 17 (a crafty lowbie alchemist could turn a healthy profit without ever fishing).
Post 1.11, the costs have equalized with ten eels/oils selling for 9 gold (although the writ asks for twenty eels...so full stacks might sell quicker, albeit for similar profit). Mainly due to overproduction, IMO.
Why the overproduction? Two-fold. There's a new use for them and they school up, now. If prices spiked, I missed it. All I noticed were greater supplies and lower costs. Which means that people with non-writ uses for the eels, making oil or superior defense potions, have seen the prices of those items fall in concert with eel prices.
Of course, what's happening on your server can be entirely different.
If you have the storage, I'd consider holding the eels until later, and dribbling them into the market rather than flooding it.