Updated July 2016: The Portland Aquarium is now closed. The building has been torn down and will soon be replaced with a Goodwill.
The Portland Aquarium is actually located in Milwaukie, which is 4 miles from my house.
It is not a world-class aquarium, but is well-staffed by biologists and has plenty of tanks and hands-on areas. We visited on a Sunday, and it was pretty crowded. They have birthday party areas and a playground/jungle gym area for kids.
Two rooms were advertised with "coming soon" exhibits: birds and otters.
I don't think I'll be likely to return until: a) the birds and otters arrive, and b) my toddlers are a little older. They were more interested in running around than actually watching the fish.
The aquarium has fish, eels, jellyfish, starfish, several stingrays, and I saw one tiny shark. I'm not a biologist so I may have named those things incorrectly, but in layman's terms, that's what I saw.
It's dark inside, so these are some not-so-great pictures taken with my phone.