O

Odd-year run
A population of fish that returns to its natural spawning grounds in odd numbered years, such as the pink salmon.

Offset hook
A hook with the point bent at a slight angle to the shank. If you lay this kind of hook down, it will not sit flat.

Oligotrophic
A body of water that is deficient in dissolved nutrients, but can be rich in oxygen.

Olivettes
A teardrop-shaped weight, used as a bulk in pole float rigs, that threads on to the line and is held in place with shot or a small plastic peg.

Open-end swimfeeders
A plastic swimfeeder with no end caps, so that it can be filled with groundbait. It is punched with holes to quicken the release of its contents in the water.

Open water
Upper water layer of a lake, from the outside edge of the first major drop-off down to the deep-water zone

Opercle
Refers to the largest bone in the operculum.

Operculum
The gill cover.

Optimum Yield
(OY) The yield from a fishery which provides the greatest overall benefit to the nation with particular reference to food production and recreational opportunities; it is based on MSY as modified by economic, social or ecological factors. Precision and Accuracy Precision is the closeness to each other of repeated measurements of the same quantity or object, while accuracy is closeness of a measured or computed value to its true value.

Organic Baits
Minnows, insects, worms, fish eggs, cut bait, cheese, or similar substances used as a lure.

Outmigration
The migration of fish down the river system to the ocean.

Outplanting
Hatchery reared fish released into streams for rearing and maturing away from the hatchery sites.

Outpoint hook
A hook with the point curved slightly away from the shank, to make it more difficult for a biting fish to eject the bait without the point pricking its mouth. Outpoint hooks are mostly used with hair-rigged baits.

Oxbow
A U shaped bend in a river or stream.