The animals of the aquarium can be broadly divided into three groups, the fish, the sharks and the invertebrates. Each group has special needs and the exhibits are all designed to accommodate these needs. Over 2 500 species of fish and sharks are known to occur in southern African waters, making up almost 16% of all known marine fish species in the world. About 16% of these fish species are endemic, which means that they are not found anywhere else in the world. The diversity of invertebrates is even more impressive and there are many thousands of species found in southern African waters. The greatest diversity is found along the eastern seaboard, caused by both the warm Agulhas Current flowing along the coast and the range of habitats including estuaries, coral reefs, mangroves, mud flats, sandy beaches, rocky shores and a variety of deep ocean habitats.
 
The warm waters of the KwaZulu-Natal and southern Mozambique coast form the southern range of many tropical fish found in the Western Indian Ocean. The KwaZulu-Natal coast between St. Lucia and northern Eastern Cape is the transition zone between sub-tropical and warm temperate zones, enabling a rich diversity of fish to thrive. Many of these fish are confined to the shallow coastal waters of the continental shelf which occurs to a depth of 200 metres. The coral reefs in northern KwaZulu-Natal are especially rich in fish diversity.