1 RANDOM COLOR - INCLUDES 3 MINI AQUARIUM TOYS - These tiny fish animals inside the mini aquarium are one of those grow pets that slowly expand and grow after being submerged with water. The animals start out tiny, but grow up to 5x their original size. Fill the little aquarium with water and they will slowly grow up to about 1" long after about 48 hours! Dry out and use it again. It shrinks with salty water though most shrink simply from air after being removed from water. Ages 6+. Each plastic aquarium is 3" x 2" x 1.25". Expandable water toys or grow-in-water toys are made from a superabsorbent polymer. Superabsorbent polymers are long chains of molecules that soak up tremendous amounts of water because the water is drawn into and held by the molecules of the polymer. These polymers can absorb as much as 500 times their weight in plain water. They are toys that expand after putting them into water for several days.