Heh, why not something like the Leviathans, in Farscape?
Here's my version:
They're a migrating species, space-born, that fly from one star system to another. They enter some sort of hibernation, to survive the interstellar space and, when they approach a star, they 'wake up' and go into low orbit over a gas giant. They consume part of its top atmospheric layer, which they then compress inside them, in specialized organs. Then they use it as fuel, expelling it at high pressure, sort of like the siphon of an octopus.
They give birth to a high number of young, which the males protect by keeping them into 'fighterbays', sort of like sea horses or kangaroos. If the adults find themselves under attack, the young play the role of fighters. They grow by feeding off their male protector during interstellar flight; if it takes too long for the father to reach another star system, or if he is housing too many larvae, he will die.
They defend themselves with electric discharges, like electric ray fish. Those electric discharges can completely fry the electronic systems of any fighter and can cause serious damage to capital ship subsystems.
