Gibrien gives you container of fingerlings to release. There are four varieties, and the one you get is random. When you are near the release location the fingerlings will automatically release; you may have to swim to release them.
Release crappie fingerlings into a narrow stream beneath a small lake --- where the Upper Emerald River flows out of Emerald Lake around ( -740, 36, 227 ) /waypoint -740, 36, 227.
Release freshwater salmon fingerlings in the pond at Tunare's Sapling around ( -64, -10, 61 ) /waypoint -64, -10, 61. (need to go underwater at location)
Release catfish fingerlings in a deep quiet pool --- Emerald Lake around ( -766, 37, 254 ) /waypoint -766, 37, 254.
Release fathead fingerlings in a boggy pond --- Opal Pond around ( 167, 2, 82 ) /waypoint 167, 2, 82.
Doing this quest is the quickest method, if a bit tedious. What you're looking for is the 'Fathead Fingerlings' or 'freshwater salmon fingerlings' . Keep deleting your quest till you get the one that has you dropping these off.
The Salmon are released in the Tunare's Sapling Pond near the river outflow. These can both be done most quickly by taking the quest, immediately walking over to the travel pad and selecting 'Old Kelethin Acorn Lift'. On arrival walk either left along the edge of the platform (salmon), or right up the branch (fathead), till you are above the water needed and then drop off the platform to safely land in the water. TheOpal pond will instantly update the quest, but in Tunare's Sapling Pond you will need to swim round to the left side of the river exit till the quest updates. Then simply get out and run back to the Old Kelethin lift, and use the transport pad to return the quest at the Near Residential Aerie..