M. surmuletus is perhaps somewhat more prized.[2] The ancient Romans reared them in ponds where they were attended and caressed by their owners, and taught to come to be fed at the sound of the voice or bell of the keeper. Specimens were sometimes sold for their weight in silver. Pliny cites a case in which a large sum was paid for a single fish, and an extraordinary expenditure of time was lavished upon these slow-learning pets.