We have a salt water (marine) aquarium and now that I look closer at your photo, I wonder if the aquarium is perhaps a marine tank with salt water fish? If it is a salt water aquarium, the yellow fish might be Goby:
http://www.bing.com/images/sea...
The fish with black spots reminds me of a Grouper:
http://www.bing.com/images/sea... but Grouper get quite large and although many who have marine aquariums put Grouper in their tanks, the fish outgrow that habitat quickly!
