www.visitouterhebrides.co.uk/.../red-throated-diver-loch-langavat-p5304...
During the summer months Red-throated divers breed on small fresh water lochs commute to the sea for fishing. They are a "SLIM ELEGANT" water bird that are never seen on dry land.
Now I'm more confused???? Baldric's link is to a water bird not a fish.......... and so doesn't agree with the clue (as written).
But I don't know of any red throated fish (if fish have throats), so I reckon it's a typo in the clue and the answer has to be DIVER