Contrary to many superhero comics, neither Hellboy, BPRD,... have an ongoing series. They are published in one-shots and miniseries. So Abe Sapien doesn't really have his own series, but there were/are comics centred on him. I've only read two: "The Drowning" which is pretty stand-alone as I recall and "Drums of the Dead" which is part of the first BPRD collection.