Blackfin Darter
From Wowpedia
A quest objective of the 
[70] Bait Bandits daily quest for fishing.
Source
The elusive Blackfin Darter can only be caught in the streams of Terokkar, since it prefers flowing water to the still deep waters of the lakes. It can also be caught in the Cenarion Thicket Moonwell. It is quite easily caught in the river area opposite the waterfall immediately to the north side of the bridge at the entrance to Stonebreaker Hold.
Patch Changes
Patch 2.4.0 (2008-03-25): Added
