Plecos are often purchased as living aquarium scrub brushes. A customer sees algae, brings home a small sucker-mouthed catfish, and expects it to clean the tank while surviving on whatever it finds. That plan overlooks one important detail: a pleco is an animal, not maintenance equipment. Different pleco species vary considerably in adult size, diet, behavior, and water requirements. Choosing the right one begins with learning exactly which pleco is being sold.

Goldfish, Carassius auratus, are domesticated freshwater fish descended from wild carp. Their long history in aquariums and ponds has produced many varieties, from streamlined common goldfish to round-bodied fancies with flowing fins. They are popular for good reason. Goldfish are active, visible during the day, and full of personality. Many learn where food appears, respond to the person who feeds them, and investigate changes in their environment.