"The feeding of the fish was a matter of more interest, and it was striking to observe that the angel-fish and groupers were able to recognize their respective summons to food, for when the keeper tapped one portion of the bridge it gave a sharp cracking sound to which the angel-fish came flocking, while in calling the groupers and other fish, he hit another portion of the bridge, which reverberated in a different tone, and the larger fish dashed through the water to the appointed places."