Loosing Nemo: The Story of A Transgender Fish


We all enjoyed watching the adventure of Nemo’s father searching the ocean for his son but little people know how amazing these beautiful fish are in real life. From sex changes to anxious juveniles, Clown fish (Amphiprioninae) also known as anemone fish, are rather peculiar animals. Unfortunately, after the movie the demand for clown fish in the pet industry tripled, leading to scientists heavily researching the species in order to better understand how to conserve it.


Clown fish are endemic to the Pacific and Indian oceans embracing the Red Sea and the Barrier Reef in Australia. Although the physical colouring predominantly depends upon the type of species most clown fish have the same orange and white pattern as Nemo did. The largest clown fish can grow to a size of about 18 cm, with the smallest measuring 10cm. As seen in the movie, clown fish form a symbiotic relationship with the sea anemone they live in. Symbiosis describes the two way relationship in which both species benefit from a partnership.


The clown fish are the only fish that do not get stung by the tentacles of the sea anemones. The fish have a slimy mucus covering their skin, it is thought to be made up of some sort of sugar compound, rather than proteins, which perhaps make the anemone not recognise the fish as food. The clown fish eat various small invertebrates and algae that could harm the anemone. Their faeces also serves to help fertilise the anemone, as well as providing the anemone better water circulation by its frequent activity in and around their home. In return the sea anemone offers a great deal of protection for the clown fish from predators. The fish also gets food in the way of scraps from the anemone’s food. The perfect partnership for surviving the hussle and bussle of coral reef systems.


Moving on, perhaps the most peculiar trait of the clown fish is its ability to change sex. Clown fish are sequential hermaphrodites, all been born male and only certain individuals changing to become female. The clown fish live in well organised social schools made up of all males and just one female – the lone female being the dominant and generally the largest fish in the group. The second in command is usually the largest, most aggressive male of the group. He uses his size to ensure the other males stay small and so he is the only one to mate with the female.


This is the part were the movie would have got a bit weird. If the female dies, the dominate male will get the first choice of food and will quickly become dominate and become a female. So Nemo’s father would have changed to become Nemo’s mother? This new female of the group will then start to breed with the new largest, most aggressive male. At the same time all the other fish in the group will move up one in the pecking order. It is thought that this peculiar ability to change sex developed because clown fish almost never stray very far away from their homes in sea anemones. Thus, if not for their ability to adapt to potentially limited mating partners in their local area, they may not get a chance to breed at all.


Unfortunately changing into women will not help the populations against worries such as habitat destruction and climate change. The coral reef habitats of which these fish call home are under an onslaught of threats; over-fishing, rising sea levels, coral bleaching and ocean acidification. It is well documented that our planets coral reef systems are under threat and need our help. New research also suggests that ocean acidification could be having psychological effects on the fish in the ocean and clown fish are of no exception.


It has been found that the acidifying oceans are causing fish to become more anxious. Alteration of GABA receptor function, which play a key role in modulating activity in the brain and nervous system, are causing alarming changes in behaviour. Fish are losing their ability to sense predators making them more vulnerable on the reef. Perhaps most worrying are the effects on the ability to detect the chemical signals necessary for navigating to and locating their anemone homes. Juvenile fish that are unable to locate new anemones to inhabit also have a much greater chance of returning to their original place of birth, increasing the likelihood of inbreeding. Juvenile clown fish have been found to search over 400km in order to find new homes to inhabit, if these fish lose the ability to find suitable homes, they may be searching for ever, just like Nemo.


Studies are suggesting that the threat of habitat destruction coupled with the high levels of harvest for the pet trade could lead to the clown fish populations drastically dropping. Around 60,000 clown fish are harvested each year for the pet trade. With population reductions so drastic it’s hard to see how the process can be sustainable. What can we do to help keep Nemo and his kin alive? Firstly never buy tropical reef fish, even if they are captive bred it will encourage others to keep exotic fish, they are better left in the ocean. Most importantly we must do as much as we individually can to halt the effects of climate change that are killing the reefs of our world.


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