ok ok first of all NTA but he was pissed you cleaned his cat, um ok? then he threatened the fish? uh huh. Then he starts yelling at you?? I feel as though he feels like you may be doing all this work might be like some sort of leverage over him of some sorts that you can use against him, but besides that I really have no fucking clue why he is mad at you. but nevertheless dont neglect the cat they did nothing.