Well this object has alot of flaws, you should start with doing the part that you think will be the most detailed, the eye for an example so that you dont stand there with a good model and realise that you cant do the eyes with that poly count.

Second of all, you should "attach" the fins so you dont have that ugly line there, you should also make it thiner by the end of the fins. And what is that thing at the "main fin" looks like a miner fin in the larger fin or something.