Penn Plax Stone Hideaway, Aquarium Decorations Rock Hideout, Small Decor For Fish Tank or Mini Bowl, Best for Turtle Terrarium, Betta Fish Accessories, or Goldfish House PERFECT FOR TERRITORIAL FISH: the swim-through area allows territorial fish to have their own space, which reduces both stress and aggression. COMBINE FOR A CUSTOM LOOK: sold separately are different sizes of the Penn Plax Stone Hideaway which can be stacked up together for a great custom look. SAFE FOR FRESHWATER AND MARINE FISH: the product is safe for your freshwater and saltwater aquariums. BEAUTIFUL REALISTIC GRANITE LOOK: made of fish-safe durable resin, the granite-look mimics what would be found in your fishs natural environment.