The presentation is really detailed for a Game Boy game (I mean look at the octopus). The soundtrack is fire too, the main theme reminds me of a Mega Man track, as weird as that sounds, and I like that each trader at the shop has their own unique theme. I think it's a good idea to play as a giant octopus causing destruction and trading in loot for money.
I wasn't a fan of the gameplay itself, to be honest, as all it amounts to is mashing the attack button to destroy ships and it got kind of boring after a while. I also found it difficult to understand the trading aspect at first due to lack of clarity in some visuals (it was hard to see the items at the bottom. Honestly, if the game were finished, I would prefer to have a fail state and different ways you can attack ships, sometimes hostile ones. Maybe have a secondary reason to collect tons of gold, too, like upgrades.
Overall, though, keep up the good work and again, great job on the presentation.
Speaking of sea creatures, you could play my goldfish game if you like.