Whitebait life cycle...

[MikeFish]

Just curious...

Most other fish migrations from sea to river are mature adults returning to spawn eg salmon, sea trout etc) but thats not the case with whitebait is it as its juviniles that are returning ?

Adult whitebait spawns in suitable wet lands.

juviniles ? head out to sea

whitebait come back up the river (1 year later ?)

whitebait disperse through out wetlands and grow into adults before spawning again ? How long does this take ?

Is this basically correct ?

Also noticed a few of the smelt i caught at the mouth of lake ellesmere are completely clear like giant whitebait, looking closely you can see the blood pumping from the heart in little squirts and they have broght blue eyes. But at the other end of the lake they are colored up, a lot darker with distinctive blue sheen and no internal organs visible. Both types smell strongly of cucumber, are there multiple species of smelt or is it just the difference between sea and fresh water habitat ?

[blueether]

Just curious...

Most other fish migrations from sea to river are mature adults returning to spawn eg salmon, sea trout etc) but thats not the case with whitebait is it as its juviniles that are returning ?

Adult whitebait spawns in suitable wet lands.

juviniles ? head out to sea

whitebait come back up the river (1 year later ?)

whitebait disperse through out wetlands and grow into adults before spawning again ? How long does this take ?

Is this basically correct ?

more or less

Adult whitebait species all spawn in different places, Inanga in the lowland streams/rivers, Banded and Giant Kokopu in wetlands/slower streams, Short-jawed Kokopu and Karo in faster streams with native bush cover. All in the autumn.

The larvae (fry) get washed out to sea that autumn and return the next spring, so about 4 or 5 months?

The whitebait then migrate to their preferred habitat to grow and then spawn.

Inanga this all happens in one year but the other Galaxiid species take several years to get to a breading age.

[Stella]

This thing of moving between salt and freshwater is called diadromy.

There are three main kinds of diadromy:

catadromy - main growth in freshwater then migrating to sea to spawn (eels, black flounder)

anadromy - mostly growing at sea, migrating inland to mature and spawn (smelt, salmon)

amphidromy - mostly living in freshwater, fry go to sea for a short period of growth before returning to do the rest of their growth. (whitebait, bullies and probably torrentfish)

Whitebait (inanga, koaro, banded kokopu, giant kokopu, shortjaw kokopu) lay their eggs in freshwater (well on the banks during high tides or floods) in autumn and the fry are washed out to sea or at the mouths of estuaries. Three months later in spring they migrate back as whitebait then stay in the freshwater streams for the rest of their lives.

Inanga, the most common whitebait, is a little bit of an odd one. It is mostly described as amphidromous, but some describe it as catadromous. This is because the adults migrate back to the tidal areas to spawn. They may not necessarily re-enter salt water, but near enough. They mostly die after spawning, so they only live one year.

Fish that move from salt to freshwater undergo some pretty major physiological changes to cope with the chemistry change, but also to deal with the different environments. In the sea they are zipping around in the zooplankton (tiny mid-water critters), eating smaller things and being eaten by bigger things. There is nothing to hide behind or blend in with, so most zooplankton creatures are see-through to avoid being eaten. WHen they come into freshwater they can hide and blend in with other things, so they change colour. You will also notice that ones that have been in freshwater for a while are SHORTER than fresh-run whitebait. I guess this is to cope in the changing environment (flowing water).

(The above goes for both whitebait/galaxias and smelt)

There are two species of smelt, but the other one is in Canterbury, and they look very very similar.