Objectives

Wild ayu resources change every year and they may not always fulfill the needs of fishermen. The Gifu Prefectural Ayu Hatchery was established in 1983 by joint investment of Gifu Prefecture and the Gifu Prefecture Federation of Fishermen’s Cooperatives in order to supplement shortages in wild ayu resources and to provide juvenile ayu generated from wild ayu for release into rivers.

Gifu Prefecture Hatchery

■Origin of Adult Ayu

It is preferable not to release groups that are genetically different　from ayu originally live in the area in terms of continuous management of wild fish groups.
In order to keep genetic diversity specific to ayu in the Nagara River, we catch matured ayu mainly from the Nagara River and artificially collect eggs from them.

■ Effective population size

The number of individuals that contribute to spawning and provide their genes to the next generation is referred to as the “effective population size.”
It is recommended to use at least 50 individual adult ayu in order to maintain genetic diversity. Based on this standard, more than 1,500 individual males and more than 4,000 individual females are used for artificial fertilization every year in this hatchery.

■ Number of Generations

When breeding fish continuously, much of the genetic diversity held by wild groups will be lost due to evolutionary reaction (genetic drift or natural selection).
In order to reduce this risk, continuous breeding of ayu is not implemented in principle in this hatchery.

Outline of Rearing juvenile Ayu

① Culture of feed for larval fish （Mid September to January）
② Roe Harvest （Early October to Mid November）
③ Hatching （About 15 days after fertilization）
④ Care of larval fish （October to February）
⑤ Sorting large and small grown fish （December to February）
⑥ Rearing juvenile fish （from February）
⑦ Shipment of juvenile fish （from April)

Net fishing (soji) at the Nagara River