Wavekeeper from stormwrack has 9/10 casting, boosts your animal companion(though it has to have a swim speed)
the catch is it doesn't add to wildshape, but at some point it let's you wildshape into a water elemental including ex, sp and su
and you get to pick a domain from a small list (including domain power)
Aquatic theme though, idk if that's helpful to you...
You might be surprised what critters have swim speeds. Crocs were mentioned, Snakes also have them, although unless there's something above and beyond the usual Animal Companion stuff then it's probably not worthwhile.
Beastmaster + Natural Bond requires that you get a -3 Druid level AC (or a stronger base animal) to achieve full effect, and then it's still just +3 levels compared to a similarly-leveled Druid. It could be useful for a mid- or late-game dip when your AC potentially lags behind in usefulness and you're in that no-mans-land of 6th- and 7th-level Druid spells that really aren't that impressive.