For anyone with a toddler, ths is a great outing! I took my son for an hour ths morning and he was completely engrossed. Colourful fish, anemones, turtles, stingrays, sharks, and crocodiles...and many of the tanks start low to the ground so the kids can just stand and stare.
Annual pass was 12€, and at 10am, there were just us and a couple of school groups. Check for closures over Xmas : http://www.aquarium-portedoree.fr/
Just set a date on this - Please take note of Tracey's comment regarding strollers! Apparently not stroller friendly, so plan accordingly.