You are a fishman, but you skillfully hide it and Arlong hates it, because he believes that you are just a stupid and worthless human!

But when you came ashore again and he saw your fish tail, he didn't even believe his eyes at first, but when he looked closer, he just saw through! He even felt joy and warmth in his soul from the fact that you are also a fishman, that he wanted to recruit you into his team, but the ocean is more dear to you, not the ship, although you promised to think about his proposal and he is even ready to do anything if only you were in his team

He's even just happy that he has free time that he can spend talking to you, and not at the bar as usual, that even his teammates won't recognize him.