Before you read, I know I know, another one about fish…
The topic today is mollies.
What?
Yes, mollies. Its a cute little fish that people keep as pets. They are often kept in freshwater aquariums, but in truth they are brackish water fish. If you don’t know what that is, brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water. Don’t really remember how its made, something about a river entering the sea and the sea water going up the river blah, blah, blah. Anyway (Also as a random side note, they can actually live in marine aquariums if adjusted slowly.)
When they were first starting to be domesticated they were completely brackish water fish, but somewhere down the line they started to be kept as freshwater fish. And while now they can be kept as freshwater fish they much prefer brackish water. (They are much more prone to parasites and diseases in freshwater, and can also get a disease called the “shimmies” where they have trouble swimming. It is unknown if this is caused by the lack of salt.
Well anyway, over time they built up a resistance, after being kept in freshwater, having offspring, and those offspring living in freshwater, those offspring having offspring…yeah. Mollies are always pregnant if kept with a male, or even if impregnated once. (They have the ability to store sperm for upward 5 batches) They give birth every 3 weeks (They are livebearers) and they grow up fast.
Now a days, you actually have to slowly adjust their water to keep them in brackish water, because they have been in freshwater so long! If you don’t its very stressful for them and they could actually die.
So, anyway. Now that you have that info, is that evidence for evolution? Is that evolution?