That's too big of bite!

[Browning Guy]

Told you so. 

Just when you thought you had seen it all. A little fish with a big attitude that finally caught up with him.

[Quillback]

Dang. that bass could've grown up and been caught on a big swimbait.

[bfishn]

Walleye start doing that at ~1/4" long and <2 weeks old if there's a shortage of the right sized live food.

Swallowing a whole fish of equal size isn't possible of course. They swim around with their sibling hanging out of their mouth like that picture for a couple days till the body rots off, then they swallow the head. After a few episodes of that, the cannibals are enough bigger (and stronger) than their siblings to really take advantage of the situation. In a fish-eat-fish world, your brother might also be your breakfast.