Re: NANFA-- Off-topic, boring fact for a Tuesday evening

Pete Liptrot (
Tue, 23 Jul 2002 22:19:28 +0100

> Is their diminutive size due to lack food or food variety or both?
Probably a combination of both. Invertebrate diversity in these streams is
much reduced, and so they are largely dependent on terrestrial/flying
invertebrates being blown or washed in. The only other fish species likely
to occur there, if at all, would be I imagine Cottus gobio (other than Trout
they are always the species I find furthest up the hill streams around here,
but they don't like it too acidic).

>When you say mature at 6" do you mean full sized or reproductively mature.
Full size. Such fish are usually also characteristically highly coloured.

>Are they reproductively mature at 6" in other streams
I think Salmo trutta does have 'sneaker' males (as do Oncorhynchus, don't
they?), that may be reproductively mature at very small sizes, but these
usually retain the potential to continue to grow when in more productive

>or something in the food that promotes early maturation?
It isn't early maturation that is the case here, but a greatly reduced
growth limited by a unpredictable and variable food source.
Salmo trutta is a fascinating and highly variable species, that in the past
was split up into many different species just within the British Isles. Some
of the Irish Lochs have distinct trophically specialized reproductively
isolated populations that I should imagine actually are well on their way to
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