The bluegill bully (Gobiomorphus hubbsi) is a fish in the family Eleotridae that is endemic to New Zealand.

[5] They are amphidromous (meaning that they migrate from fresh water to the seas, or vice versa, but not for the purpose of breeding).

The eggs are laid in fresh water and on hatching, the larvae are carried to sea for the first stage of their development.

It has been proposed that avoiding water abstraction in lower reaches of waterways in the hours post sunset could significantly improve survival of larvae.

[7] The young fish return to fresh water after a few months and continue to slowly migrate upstream as they get older.