Hi all,
If you look at this list you'd think any wood would be bad for fish, even oak and beech
Yes, I think you are right and it is also sort of the point. Wood is built of lignin <"
because it is very difficult to degrade">. The harder, and more rot resistant, a wood is the more lignin it has in it and it may also have residual tannins etc.
It is always going to be a balance between <"
rot resistance and toxicity">.
I look at it as any dead heart wood, that has soaked for a while, is unlikely to be toxic, because any soluble compounds will have been lost. If you keep a wood eating <"(
xylophagous) fish like a Panaqolus sp."> they maybe more at risk.
Trees don't want wood boring insects and fungi degrading their wood and they can only grow into massive, long lived, trees by protecting the water conducting xylem vessels in the wood. They also need to protect their leaves, shoots and sap-wood and particularly the cambial layer, containing the phloem, just below the bark. They do this by producing toxic alkaloids, latex, tannins, resins etc.
The cells of all the wood under the cambial layer are dead, so that the tree can't actively protect them but they are still essential structural support and also to transport water (and mineral nutrients as ions) to the leaves. Transpiration is a passive process, where the evaporation from the leaf stomata maintains a continuous column of water (the transpiration stream) all the way from root to leaf.
cheers Darrel