[Space/Aliens] Reproductive Features: alien, exotic and weird ideas

[Fish]

Interesting thought experiment. You could hardly do worse than to look at the various strange configurations on Earth.

Gender differentiation, for instance, could be achieved, through temperature. At a certain temperature, the offspring are always male; above or below that, female. Primarily this is done by reptiles, I believe.

There is also the example of the clownfish, which engages in sequential hermaphroditism. There is one female and one dominant male, forming a breeding pair; all the rest of the fish are prepubescent males. When the female dies, the dominant male becomes female, and a new male is selected.

Also consider the matter of offspring: generating new life forms takes extra calories. This can be done through sexual cannibalism, where the body of one parent is consumed by the other in order to provide the extra biomass with which to make the eggs. An extreme case is the angler fish, where the tiny male actually fuses with the large female and atrophies away until virtually nothing of him is left.