How do I know if my fish is pregnant?

how do I now if my fish is pregnant or not ?

well it all depends on what type of fish you have as some of them dont get pregnanat they just lay the eggs and then the male fertilises them outside of the body!!!, others can have the eggs inside of them in that case the fish might be bigger , but it all depends on the type of fosh, what fish is it?
X

Not sure, but someone once told me there is a black spot that you can see on the side of the fish that only shows up when that are pregnant. If the fish is in with others they will eat the eggs and you would never know that it had babies.

is my tetra fish pregnant?