My 9in. oscar has for the past 3 weeks taken to swimming in the rear of the tank, down low and thru the plants as if looking for something. His appetite and energy seem to have lowered also. He used to be up front and center 24 hours a day. My tank is over stocked but the water quality is good. H also seems to be much less aggressive, even a bit timid. He/she was also always the tank alpha. Is this a sick fish or is there something else going on. I dont know if its a male or female and there are no other oscars in the tank The tank is a 55 (soon to be a 125) and contains a 6"buttikoferi,a 6"red spootted cichlid,a 9" pacu and two 4"jd's and a 5" feather fin cat.I know , I know .Im trying to set the other one up.