wowlolInland zone fishing is very often (not always) the same in any open water within the zone.
That said, I have seen confirmed catches of the Dark Herring in:
*
The water next to Valgarde
*
The rivers surrounding Cauldros Isle
*
The lake north of Skörn (where I caught it myself)
*
Grizzly Hills rivers, open water
All of these reported catches included Bonescale Snapper, Fangtooth Herring and Glacial Salmon. This means that wherever all of these three fish can be caught would most likely be the place to fish the Dark Herring as well. I would even say, as the fish is called Dark Herring, that wherever the Fangtooth Herring can be caught, the Dark one can be caught too. Why? Because this is how fishing mechanics in this game generally works.
Don't bother fishing where you cannot catch either of these above mentioned fish, and to be absolutely safe make sure you catch Fangtooth Herrings every now and then.
With that clear, let's move on to fishing skill. I skilled up while fishing for this, using lures until I was maxed base fishing skill (450) because I noticed the "Your fish got away" messages had disappeared. I used my Arcanite Fishing Pole with a fishing line attached, meaning my skill was 488 most of the time. No lures, just maxed skill and my fishing pole.
Unless you are getting "Your fish got away" messages, your fishing skill is definitely high enough to catch the Dark Herring. There is no fish in the entire game that requires a significantly higher fishing skill than the other fish in the same water to be caught.
Last, about level. I have read about one level 68 guy catching this on another forum. Two level 70 people has written above they have caught it. Unless Blizzard decided to put some weird level requirement bound to the levels of the zone's quests (I can't promise anything here), this can probably be caught no matter what level you are.
Don't worry about not being able to catch this depending on your level. Again, no fish in the game (as far as I know) requires a specific level to be caught. Instead, other factors decided whether you can catch them, such as having flying mount, level requirement on the fish itself (such as this one) or lots of mobs near the water.
Instead of getting too hung up on details like this and trying to find reasons why you haven't caught it yet, try to face the fact that this is an extremely rare fish. This will take a while to get, and the people who post their results are often the lucky ones who haven't been spending countless of times without results. Adapt to what I have said above and then you are fine. The only remaining thing is a lot of time and patience.
That said, I have seen confirmed catches of the Dark Herring in:
*
The water next to Valgarde
*
The rivers surrounding Cauldros Isle
*
The lake north of Skörn (where I caught it myself)
*
Grizzly Hills rivers, open water
All of these reported catches included Bonescale Snapper, Fangtooth Herring and Glacial Salmon. This means that wherever all of these three fish can be caught would most likely be the place to fish the Dark Herring as well. I would even say, as the fish is called Dark Herring, that wherever the Fangtooth Herring can be caught, the Dark one can be caught too. Why? Because this is how fishing mechanics in this game generally works.
Don't bother fishing where you cannot catch either of these above mentioned fish, and to be absolutely safe make sure you catch Fangtooth Herrings every now and then.
With that clear, let's move on to fishing skill. I skilled up while fishing for this, using lures until I was maxed base fishing skill (450) because I noticed the "Your fish got away" messages had disappeared. I used my Arcanite Fishing Pole with a fishing line attached, meaning my skill was 488 most of the time. No lures, just maxed skill and my fishing pole.
Unless you are getting "Your fish got away" messages, your fishing skill is definitely high enough to catch the Dark Herring. There is no fish in the entire game that requires a significantly higher fishing skill than the other fish in the same water to be caught.
Last, about level. I have read about one level 68 guy catching this on another forum. Two level 70 people has written above they have caught it. Unless Blizzard decided to put some weird level requirement bound to the levels of the zone's quests (I can't promise anything here), this can probably be caught no matter what level you are.
Don't worry about not being able to catch this depending on your level. Again, no fish in the game (as far as I know) requires a specific level to be caught. Instead, other factors decided whether you can catch them, such as having flying mount, level requirement on the fish itself (such as this one) or lots of mobs near the water.
Instead of getting too hung up on details like this and trying to find reasons why you haven't caught it yet, try to face the fact that this is an extremely rare fish. This will take a while to get, and the people who post their results are often the lucky ones who haven't been spending countless of times without results. Adapt to what I have said above and then you are fine. The only remaining thing is a lot of time and patience.