3 replies to this topic

[Sean Phillips]

I was just thinking about this and thought I'd open it up to a discussion.

I assume most of us on here are familiar enough with Rhinichthys. This genus of Cyprinids have Inferior mouths due to their primary habitat being riffles and them being bottom grazers. Many are also familiar with the fact that they adapt quite well to living and feeding in tanks with little flow such as only a sponge filter and that they will invert their bodies at an angle, sometimes even turning upside down to feed after being in such a captive environment for as little time as a few days. Well think about this. If we were to captive breed this fish hundreds or even thousands of generations inside tanks with the only flow being a sponge filter (assume that the fry would be bred with other batches to prevent genetic problems) would they eventually adapt and change the structure of their mouth to a terminal one in order to feed more easily in such an environment? Just something to think about.

[Michael Wolfe]

Philosophical musings on natural selection are not my thing but I would have to ask what would the selection criteria be? I'm not convinced that convenience would be a strong selector.

[gerald]

Maybe, but only if the ones with a normal inferior mouth get outcompeted and fail to reproduce. If there's plenty of food for everyone, or if feeding at a funny angle is no problem, then there's no selective pressure to drive the change. However, some aspects of mouth shape and teeth development may be genetically "plastic" and develop in response to how, where and what the fish actually eats as it grows. I think that's been shown with rock-scraping cichlids that grow up on flakes and pellets and rarely have reason to scrape rocks. It's not a genetic change in that case.

[Kanus]

I agree, absolutely possible so long as there is a selective pressure. Maybe if you only had food available on the underside of objects you would eventually end up with "upside-down dace" similar to the african catfish! Now there's a niche market!