Tosai,...

[JasPR]

When Sakai of Hioshima first started the 'hot house tosai' back in the 1980s by using indoor facilities with heated well water and pure oxygen, there were huge looses reported in exported fish once at their destination. His response was to first 'harden off' the fish in cooler water and more natural conditions so they became 'hardier' for the journey to the west. It is important to realize that this was all in response to those breeders who were already shipping fry to warm areas like Okinawa , Thailand, Cambodia etc for fast warm water grow out before shipping west. As a side note, I always suspected that foreign growout could have been one of the dynamics/practices that eventually brought disease back into Japan? But I digress.

I think we can all intellectually accept that koi and carp are temperate water creatures of great hardiness. And as such, can tolerate and seem to flourish in unique situations that are typically foreign to the environment they evolved in as a species and flourish in as individuals.
lower form creatures have a limited survival set , genetically speaking. So they evolve in a region of the world and spread until the limits of that genetic/metabolic reality is met and basically defeated by very different conditions. And this acts as a distribution 'wall' as the very different conditions not only disfavor the expanding species , they also favor a more locally evolved species of that very different region's parameters.
So we have tropical lower forms that spread to Florida for instance. And survive well because they can exploit that environment as their metabolic limitation are not violated.
But in teh bigger picture, salt water species can not colonize freshwater as a group because their physiology will not cope long term with such conditions.
In another example, the gulf currents bring tropical species up to the northern east coast where these tiny fry can find a habitat in bays and inlets all up the coast. There, they live and grow quite well. But as soon as temperate water conditions come in autumn, they are all killed in a matter of weeks.
These are extreme examples of the limits of adaptation of lower forms. We miss these things in koi and often are left with our own conclusions based on what dogs, cats and birds behave like. Let me say it again as I haven't in a while----
Koi's greatest gift , adaptability, is perhaps it's greatest curse.
- JR