sure thing.

The problem I have with it is that there isn't any real structure that stands out to me, it's all washed out and relaxed. Add some spots of tension and imply some bone and cartilage structure.

It's hard to say much since I don't really know what you're going for but do a search for mermen or fish beings or something. Since you're basing this off of potc I assume you've seen this already? it may help with some ideas. There were also a couple articles at cgtalk a while back.

as far as the character design I think what would make it easier on you is to take a human, and take 1 or 2 aquatic creatures and try to mix the human to meet the patterns of those aquatic creature. This will force consistency in the design and also make it more readable as a human transitioning to beast.

...sorry, I hope that was helpful at all :p
get this part down and I think you'll have something really sweet at the end of this.