I wanted to make a quick comment regarding fishes drinking water...

Freshwater fishes do not drink water. They have too much moving into them via osmosis and must excrete ridiculous amounts to maintain their salt balance. Saltwater fishes, however, do drink water. Since the salt content of seawater is so high, they have to actively drink the water through their mouth to do the same thing while their gills remove the excess salt. They excrete virtually no water.

I wish I could find the page in my Biology textbook I read this on for evidence, but that's what I remember. The joke doesn't make sense anyway, because we can assume it's a freshwater fish in the river.

Just letting you know :)

Thanks for trying to clear that out. However, I mantain that none of them do drink the water. in the sense that they do not ingest it. It goes in through their mouth, but not to the stomach. They filter it, not drink it. 

I wouldn’t call putting water in my mouth and then throwing it away drinking. I know it’s not the same, but it’s the closest thing I can imagine to expelling it through gills. Unlike cetaceans, fish don’t drink water, at least not in the way in which we define the word for us humans.

Be reasonable

Fight the faith