Cow nosed rays at Scarborough Sea Life and Marine Sanctuary are living up to their names by creating huge "cow pat scale deposits".
The rays need to be fed twice every day and are constantly on the move
Staff at the centre said the six cow nosed rays had been creating dirty work since their arrival at Easter.
Senior aquarist Derek Scoles said "mucking out" the ray tank had now become a daily duty for staff, a task which nobody had anticipated.
He said: "They never stop moving and burning up energy."
The rays are part of the centre's new Great Barrier Reef display and share a tank with a zebra shark, Port Jackson sharks and banded catsharks.
Mr Scales said the rays needed feeding twice a day and their tank was now "mucked out" each morning before the centre opened.
He said: "It's an extra duty we hadn't anticipated and which none of us enjoy.
"But it's a small price to pay for having such spectacular creatures grace our new feature."