without a doubt, my rubberlip pleco. it used to go to town on the algae in my tank and any vegetables or algae wafers i would toss in the tank, and leave a subsequent trail.
Its a toss up between my barramundi and my silver scat. The barra gets about 150 - 200 grams of food a week and has HUGE poo's. The scat is just messy. He poo's heaps, eats messy and tears everything up. Including plastic plants. He tears pieces of them off and them watches them float away. Each barramundi poo would be probably about the size of a human thumb. He does about 4 of those a day :/