Cod Do Batter
Red & Green Fish
If a fish appears as red in a tooltip then it has not yet been caught (defined by Blizzard as looted into your bags!). If a fish appears as green then it has been caught and therefore counted towards your achievement.

Why an area was selected for a "blue circle"
The choice of areas is very subjective. It might be an area conveniently nearby a faction base, an area where schools are plentiful, an area representative of a much broader area, an area safe from patrolling mobs, an area with a higher than average occurrence of a fish type, etc.

How fish were "ranked" within a blue circle
Every "blue circle" has been personally fished by this author at least 50 times and even to 200 in rare cases where I was not yet satisfied with the data. Whilst 50 is not statistically thorough to "guarantee" very rare fish are included, it suffices for fish found in the achievements.

Sometimes there is negligible difference between two fish when they are ranked. I merely use the order from my own empirical evidence. Sometimes a fish towards the end of the list has a very small chance of being fished.

I assume the player is at a fishing level high enough to ensure no fish types are excluded.

Fish caught in pools and open water are ranked together
Ranking fish found in pools alongside fish found in open water is problematic. CDB assumes that the player is mobile within the confines of the marked blue circle. As fish schools often take about one hour to respawn this necessarily means that fish only occurring in schools will be ranked quite low. Even though certain fish are almost a guaranteed catch within a school, a school is good for only 1 to about 5 casts.

In certain zones fish might only be found in a school or at least be so infrequent in open water that you are compelled to find them in schools. In such zones I try to provide at least one blue circle where the schools commonly spawn.

CDB does not match Wowhead or El's Extreme Angling
Wowhead data is not entirely reliable.This is due largely to zones being repurposed, data prior to patches also being included, and data not able to flag the time of day or season caught or if the fish was caught in a school or open water. El's Extreme Angling, which is now defunct but available through web archives, is somewhat dated and impossible to reconcile alongside other sources.

The neighbouring zones tooltip is annoying
Very much so when not fishing. That's why CDB has an on/off toggle for this feature.

Stranglethorn Vale
This pre-Cataclysm zone appears on the Eastern Kingdoms map. I provide a combined zone tooltip for the newer Northern Stranglethorn and Cape of Strangelthorn.

Silvermoon City has no zone map
It has no fish. Same applies to any other "missing" tooltips.

Abyssal Clam
These are Vashj'ir zone drops and are not actually fished.

Pygmy Suckerfish
These are a common drop all over Northrend and not at all confined to "Oceanographer" areas.

Deepsea Sagefish & Fathom Eel
Might not be found due to phasing issues in The Shimmering Expanse. Go instead to The Twilight Highlands or Uldum.

Golden Darter
Availability depends upon the time of day. See in-game CDB tooltips in Terokkar Forest for the best times. (I am amazed that nobody on Wowhead or the (now defunct) El's Extreme Angling websites had noticed this.

Where is the Goldenscale Vendorfish?
This fish is so rare that despite hundreds of casts the author was unable to acquire one. Your best option is to fish a lake in Terokkar Forest, Nagrand or Zangarmarsh. Fishing from pools/schools is NOT an absolute requirement but useful to avoid junk.