Test Kits Aquariums & Stand Equiptment Aquarium Filtration Aquarium Heating Aquarium Aeration Aquarium Cleaning Aquarium Decoration Aquarium Other Aquatics A  fish  is any  gill -bearing  aquatic   vertebrate  (or  craniate ) animal that lacks limbs with digits. Included in this definition are the living  hagfish ,  lampreys , and  cartilaginous  and