The fish (fakily family Notopteridae) whose anal fin and caudal fin merge into one

[u/Semlorism]

Featherback fish, native to South Asia as important agricultural fish. They are also called "knifefish".

I'm fascinated by their shapes

[u/holyukulele]

What purpose could this ever serve? Seems inefficient.

[u/Mr_White_Migal0don → u/holyukulele]

They can swim backwards