Mike Stevens, of Amberley, asks :-
Last season we released some whitebait into our small garden pond which has a rocky edge with long grasses. During the winter they vanished, so we assumed they had been eaten by predators. But in spring they reappeared. Where had they been hiding?
Bob McDowall, a fisheries biologist with the National Institute of Water and Air, responded.
I'm not sure that there is a known or simple answer to your question. What seems most likely is that the fish hibernated in some form in the substrate or among vegetation in the pond over the winter, perhaps driven to it by cold temperatures.
However, there is really little recorded of seasonal behavioural shifts in the whitebait species, and no known history of the whitebait galaxiids hibernating. It is well known that the various Neochanna mudfishes. like the Canterbury mudfish, will aestivate when the water in their habitat dries up in the late summer and early autumn, but that is a rather different behavioural phenomenon.
What is also known is that some eels will hibernate over the winter, again owing to cold temperatures. Also, as well, some of the galaxiids are capable of respiring (absorbing oxygen) through the skin, so this may enhance their ability to become dormant over winter.
Assuming the whitebait to be inanga whitebait, a lot is known about this species but there is no indication that they do hibernate. Inanga reach maturity some time in the autumn, and the usual pattern is for them to spawn and die (they live for only about a year). Conditions for spawning would be unsuitable in a pond, as they need tidal fluctuations as a part of their spawning stimuli, so they may now be carrying large numbers of eggs, and may shed them sometime in the next few months. They may survive this and mature again, but this doesn't happen often.