Although the gills of most teleost fish assist with the elimination of ammonia from the body and although fish virtually by definition live in an environment surrounded by water, most still have a distinct bladder for storing waste fluid. The urinary bladder of teleosts is permeable to water, though this is less true for freshwater dwelling species than saltwater ones.  : p. 219 Most fish also have an organ called a swim-bladder which is unrelated to the urinary bladder except in its membranous nature. The loaches , pilchards , and herrings are among the few types of fish in which a urinary bladder is poorly developed. It is largest in those fish which lack an air bladder, and is situated in front of the oviducts and behind the rectum . 
Its been 4 days since the last visit, and his urination stream is very very weak, followed by a few drops of thick blood.. and still a significant amount of straining. Seems to be in slight pain when urinating, however acts semi normal once back in the house (doesn’t seem lethargic, still quite alert) the blood content seems to go away and then come back; but is never more than a few drops each time… he isn’t trying to drink his own water at all, but is super hungry; I have him on the (vet suggested) royal canine urinary SO wet food; and I sneak in ample amounts of water when feeding to keep him drinking….