Alex Neptune, Dragon Thief by David Owen

Meet Alex Neptune, the boy with the power of the ocean in his hands - a brand-new hero for fans of Percy Jackson and Dragon Realm! For as long as Alex Neptune can remember, the ocean has been trying to kill him. So he's not too happy when a bunch of sea creatures drag him to the abandoned aquarium on the hill, where an imprisoned water dragon needs his help. But how can he say no to a magical myth? Recruiting his tech-genius best friend Zoey, legend-lover Anil, a sharp-shooting octopus, four acrobatic otters and a thieving seagull, Alex plots a heist to break the dragon out. And suddenly discovers the power of the ocean at his fingertips...