Interesting facts about Cuttlefish, Sepia Sp.
Cuttlefish, despite the name, are in fact not fish but molluscs. Together with octopus, squid and nautiluses they belong to the class Cephalopoda (meaning to have the head and foot joined). Cuttlefish have a large head with prominent eyes and two fins running along the side of the mantle (main body). Some species can reach maximum sizes of 50 cm, but they are usually between 15 and 25 cm and weigh between 3 and 10 kg. Cuttlefish have 8 non-retractable arms and 2 tentacles that are longer than the arms and can be retracted into the mantel cavity. Cuttlefish have an inner shell known as a cuttlebone. This is a porous, internal shell that helps to regulate their buoyancy (floating) depending on how much gas and fluid is in the chambers of the bone. Different species of cuttlefish can be identified by their bones when they are found washed up on the beach. They are primarily bottom-dwellers living on most types of sea floor substrate including, rocky, sandy and muddy bottoms as well as over sea grasses, seaweed and coral reefs to a maximum depth of 1000m. There are at least six species of cuttlefish found regularly in South African waters. The most abundant species in South Africa is the Southern cuttlefish (Sepia australis), but most frequently seen by divers is the Common cuttlefish (Sepia vermiculata) which is endemic to South Africa.
Common cuttlefish have an elongated body with a fin running down each side and can grow to 30cm in length. They are pale on the underside with constant colour-changing bands on the upper side. This band is what they use to camouflage camouflage themselves when hiding on the bottom. Common cuttlefish’s geographic home range is from southwestern Africa, around the Cape of South Africa to central Mozambique. They are mainly found in lagoons, estuaries, river mouths and around reefs in shallow waters (max 300m depth).
Cuttlefish are fast swimming animals that feed by shooting out their tentacles to catch food (small fish). They escape from predators using jet propulsion and can squirt out ink from their ink glad to confuse the predator. As a cephalopod, cuttlefish are able to quickly change colours to match the background and hide from predators.
When common cuttlefish reproduce the male uses his colour-changing skills to display dominance over other males and to attract females, but it has been found that the females prefer newly mated males (males that have just had a female) (Boal 1997). Females will mate with more than one male and store the sperm in the mantel cavity before laying her eggs. When she lays them they will be fertilised by the sperm externally. Common cuttlefish eggs are black and pea sized allowing them to attach to algae.
There are some species of cuttlefish that are in need of protection. The common cuttlefish is not seen as a threatened species due to its Data Deficient status. This status is due to the fact that little is known about them and also because there is no fishing demand on the species. They have been used as bait and food by recreational fishermen and have a potential commercial fishing value due to their size and distribution. One of the major threats to cuttlefish is ocean acidification which can create a problem for their buoyancy control.
– COASTAL FISHERY RESOURCES an easy guide The South African Institute for Aquatic Biodiversity
– Jereb P. Roper C.F.E 2005 FAO species catalogue for fishery purposes no.4 vol.1 cephalopods of the world
– Boal J.G. 1997 FEMALE CHOICE OF MALES IN CUTTLEFISH (MOLLUSCA: CEPHALOPODA) Behaviour, Vol. 134, I. 13, p. 975 – 988
– Dr J. Augustyn Our bountiful oceans. Page 29-30
– Branch G.M. Griffiths C.L Branch M.L Beckley L.E. 2010 Two Oceans, a guide to the marine life of Southern Africa