Clown Fish and Anemone

The famously known clownfish and anemone are a classic example of an obligatory mutualistic relationship. 10 species of anemone coexists with the 26 species of tropical clownfish. Within this only select pairs of anemone and clownfish are compatible; some species specific (Fautin, 1991). The individuals involved in the mutualistic relationships are known as obligatory symbionts which means they are highly dependent on each other; for a variety of beneficial reason including protection from predators, exchange of nutrients and protection from nematocyst strikes from the anemone (Fautin, 1991).

Figure 1. Photographer: Samuel Chow (2007). Clownfish protected by tentacles of anemone in obligatory mutualistic relationship.

This relationship is exclusively observed in shallow waters of the tropical Indo-Pacific, typically on or near coral reefs. In nearly all cases, an individual sea anemone or a cluster of contiguous ones is inhabited by an adult pair of anemone fish and, depending on the species of fish, in some cases by one or more juveniles (Dunn, 1981). Reproductive behaviour is constituted by both parental figures, though predominantly male orientated. The eggs are laid on the substratum beside the anemone, and whereby the male regularly exercises mouthing and fanning the eggs to keep them clean and supplying constant oxygenated water; he also removes the unfertilised eggs from the clutch to further increase the success rate of the incubating young (Allen, 1972):(Dhaneesh et al., 2009).

Anemones possess tentacles that are covered in nematocysts which are characteristic to scyphozoan and other cnidarians. Nematocyst strikes from the anemone paralyse almost any small marine organisms that comes into contact with the tentacles. They are spear like stingers that when mechanically or chemically stimulated fire and penetrate into a foreign object and release a paralysing toxin into the blood stream of the organism; the anemone is then able to digest the food (Nematocyst, 2015). Some fish try to feed on the nutrient rich tentacles of the anemone in which the clown fish’s aggression and territorial behaviour warns them off and if that fails they risk being stung by the nematocysts (Fautin, 1991).

Figure 2. Author: unknown. Firing of a nematocyst used by cnidarians for feeding

Clownfish are believed to be protected by a mucus coating produced that prevents nematocysts strikes against them. Some studies have suggested the protective feature can be of various nature including: innate, acquired or both. Some species of clownfish are suggested to be innately protected by the mucus before ever coming into contact with the anemone while other species are suggested to have an acquired mode of protection. This is seen in the behaviour of the clownfish by repeated brushing through the tentacles of the anemone to acclimate to the host before clownfish can move freely throughout the anemone. The clownfish then acquires antigens that act as a chemical camouflage preventing the nematocysts from firing (Fautin, 1991).

The anemone and clownfish actively participate in the mutualistic relationship as obligatory symbionts providing essential and beneficial natural services for each individual.

References:

ALLEN, G. R. 1972. The Anemonefishes: their Classification and Biology     (Neptune City, N. J., T. F. H. Publ., Inc. Ltd.).

DHANEESH, K., KUMAR, T. A. & SHUNMUGARAJ, T. 2009. Embryonic development of percula clownfish, Amphiprion percula (Lacepede, 1802). Middle-East J. Sci. Res, 4, 84-89.

DUNN, D. F. 1981. The Clownfish Sea Anemones: Stichodactylidae (Coelenterata: Actiniaria) and Other Sea Anemones Symbiotic with Pomacentrid Fishes. Transactions of the American Philosophical Society, 71, 3-115.

FAUTIN, D. G. 1991. The anemonefish symbiosis: what is known and what is not.

NEMATOCYST. 2015. Encyclopædia Britannica Online. Retrieved 29 May, 2015, from http://www.britannica.com/EBchecked/topic/408444/nematocyst.

Figure 1. Samuel Chow (2007). Clownfish protected by tentacles of anemone in obligatory mutualistic relationship. Retrieved from http://www.asknature.org/strategy/fb410d8500af30a5daf5b647954b7fa5#menuPopup, on 29/05/2015.

Figure 2. Author:unknown (n.d) Firing of a nematocyst used by cnidarians for feeding. Retrieved from http://reefworks.co.uk/wp-content/uploads/2011/10/nematocysts-glow-small.jpg, on 29/05/2015