Symbiotic Relationship between Sharks and the Pilot and Remora Fish
Introduction:

Symbiosis is defined as the relationship between two different organisms, and as with any relationship there are several different types (Encyclopedia Britannica, 6). The common types include commenalism where one party benefits while the other is neither harmed nor helped, mutulaism where both parties benefit and parasitic where only one party benefits while the other suffers (Encyclopedia Britannica, 6). The pilot and remora fish share a facultative mutualistic symbiotic relationship with sharks, as both parties benefit but are not entirely dependent on one another for survival. The fish eat the shark's parasites, along with other debris, maintaining the shark's health and the fish in return recieve a meal and protection due to their association with a top ocean predator (Oceanic Research Group, 1).











Shark Background:



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Sharks are found in oceans all over the world and, depending on the species, can live in the shallow ocean water or in deeper ocean waters (Oceanic Research Group, 1). A shark that is often seen taking part in a symbiotic relationship with the pilot and remora fish is the oceanic white tip shark (Carcharhinus longimanus). This shark is often found in tropical and subtropical waters deep into the ocean, noted as slow swimmers they appear to be perfect companions for the pilot and remora fish which according to a previous study seem to be drawn to drifting objects. (Gooding, 2)
The ocean's sharks, including the oceanic whitetip shark, are carnivores found at the top of the food chain with their diet mainly consisting of fish and sea dwelling invertebrates such as squid (Oceanic Research Group, 1). When hunting the shark tends to seek out the weak and injured animals, ultimately eliminating them from the ocean's ecosystem. Although they areknown as hunters they are also oppurtunistic scavengers that feed on deceased animals and any left overs from a previous kill. Their success in hunting and scavenging has much to do with their excellent senses, with their number one being smell. A clear indication of this is the documented finding that a shark is able to smell a single drop of blood diluted by millions of gallons of water, making them accurate hunters that can easily find any injured prey for hundreds of miles. In addition to their exceptional smell and great eyesight sharks have a network of pores that connect to sensory organs so that sharks can pick up on electric pulses(Oceanic Research Group, 1).
Like most sharks the oceanic white tip depends on constant movement in order to respire properly through their gills and stay alive. This constant movement of the shark then means the cleaner fish are constantly moving, and they are in fact known to follow or remain attached for long journeys in the ocean (Keyes,3).

Remora fish and Pilot fish Background:
Remora fish are found in warm tropical waters and are thin and dark ranging from about 1 to 3 feet in length with a suction cup like disc on the top of their head (Encyclopedia Britannica, 4). This suction disc plays an important part in its relationship with the shark as they use it to attach to
http://www.wildflorida.com/wildlife/fish/images/RemoraHead463.jpg
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the shark in order to successfully feed on the parasites living on the sharks skin along with other debris(Encyclopedia Britannica, 4).


Pilot fish are about 2 feet in length and have dark blue stripes with a light underside, and unlike remoras the pilot fish are not attached to the shark but instead swim alongside them for lengthy distances and time (Encyclopedia Britannica, 5). They are known to be territorial of the shark they are with and although a group of them are usually with the shark, that group is not easily infiltrated by additional pilot fish or other fish they may come across. These cleaner fish play a very important role in keeping the sharks healthy as the water they live in is very dirty and the cleaner fish will eat anything, including parasites and bodily waste, off the shark (Encyclopedia Britannica,4-6).

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~The Symbiotic Relationship~
In a paper about cleaner fish behavior and their attraction to “drifting debris” it was discovered as cleaner fish have a tendency to gather underneath these objects, following the objects along the ocean currents (Gooding, 2). The research group hypothesized, and later verified, that this behavior was done because the drifting objects provided protection, as well as a concentrated food supply (as debris and smaller organisms would attach or grow on the object) and also acted as a cleaning station where fish could clean off each other and any other organisms that came by (Gooding, 2). The often referred to symbiotic relationship between the oceanic white tip shark and the remora and pilot fish then begins to make sense, as this species of shark is a slow mover acting almost like a drifting piece of debris the fish can find sanction with.

The behavioral symbiotic relationship between cleaner fish and a pool of various sharks had been documented in a research project done in an artificial environment at SeaWorld where researchers examined the behavior of the bull shark, the lemon shark, the nurse shark, and the sandbar shark (Keyes, 3). Sharks as a whole are not usually passive animals when surrounded by potential prey but there was a definite change in their behavior when the cleaner fish were recognized, as the sharks wanted to be cleaned off. Immediately after recognizing the cleaner fish the bull sharks experienced a posture change and speed decrease. The speed decrease is the most interesting part of the behavioral changes as the bull shark cannot stop, and has an average speed of about 70 cm/s that must be maintained in order to breathe. However, in order for the fish to keep up with the animal and do its job, the shark had to slow down- which it did for about 30 seconds (Keyes, 3). The shark also positioned itself so its head was up, facing the top of the ocean surface, as if an invitation to be cleaned. The lemon shark also decreases speed, and was able to stop its respiratory system for about 150 seconds so the body, including the mouth could be inspected.The nurse shark can stop movement and does so in order to allow the cleaner fish to remove debris and parasites. The sandbar shark however did not recognize the cleaner fish and acted aggressively towards it, flicking its tail and swimming off (Keyes, 3). Although this research experiment provided some valuable information on the behavioral changes of sharks, these results have yet to be documented in the wild and failed to include other shark species known to have symbiotic encounters with cleaner fish, such as the oceanic whitetip sharks.

In the shark and remora’s specific mutual symbiosis the remora uses its suction cup found on the top of its head to attach to the shark's underside and then feed. It easily removes the parasites and waste debris from the ocean for its own intake (Encyclopedia Britannica, 4). In addition to the food it recieves from being attached to the shark they are also protected from other predators and receive a free ride to other parts of the ocean so they don’t have a large travel energy cost. In the shark and pilot fish specific mutual symbiotic relationship the pilot fish swim alongside the shark garnering protection as well as food from picking off parasites and debris like the remora do but more so gains their benefit from eating scraps from a shark's kill or any remains it may come across in the ocean. In both scenarios the shark's benefit of the relationship is the removal of parasites and debris. The cleaning of the shark's body, including the mouth, allows for it's health to be maintained. As both the shark and the fish gain a positive outcome from having a relationship with one another, but do not rely on each other for species survival their symbiosis is considered facultative and mutual (Encyclopedia Britannica,4-6).


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REFERENCES

1. "Sharks and How They Live." O.R.G Educational Films.Oceanic Research Group. 1995. <http://www.oceanicresearch.org/education/films/sharkspt.html>
2."Ecological Significance of a Drifting Object to Pelagic Fishes" Reginald M. Gooding et al. Pacific Science. Vol 21 (1967). <http://scholarspace.manoa.hawaii.edu/bitstream/handle/10125/7839/vol21n4-486-497.pdf?sequence=1>
3. "Sharks: An Unusual Example of Cleaning Symbiosis." Raymond S. Keyes. Copeia. Vol. 1982, No. 1 (Feb. 23, 1982), pp. 225-227
Published by: American Society of Ichthyologists and Herpetologists < http://www.jstor.org/stable/1444305>

4."Remora." Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica, 2011. Web. 27 Apr. 2011. <http://www.britannica.com/EBchecked/topic/497706/remora>.
5."Pilot Fish." Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica, 2011. Web. 27 Apr. 2011. <http://www.britannica.com/EBchecked/topic/460635/pilot-fish>.
6."Symbiosis." Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica, 2011. Web. 27 Apr. 2011. <http://www.britannica.com/EBchecked/topic/577677/symbiosis>.