"So long and thanks for all the fish."
Translation:Hoşça kal ve bütün balıklar için teşekkürler.
I'm not certain, but I believe that would mean "thanks for the entire fish" rather than "thanks for all the fish" (the second one indicating that you received more than one fish).
It's a bit ambiguous in English, since the word "fish" can be either singular or plural: "That's a big fish!" / "He ate three fish."
"Teşekkürler" can stand on its own. (I don't know why, to be honest, but it's just like English: Thanks!). However, "teşekkür" needs an auxilary/helping verb ("etmek").
- Teşekkürler = Thanks
- Teşekkür ederim = I thank you ("sana/size" is implied)
You will find "etmek" popping up all over the place to help out. :-)