Remora

You might have heard about hitch-hiking rides in humans, but surprisingly there is a fish species that has the capacity to hitch a ride by attaching themselves to other fishes. It is called the remora fish. The remora fish is a pelagic marine fish found in warmer parts of most oceans. This fish is famous for its suction cap at its head plate, which it uses to suck onto other creatures in the ocean.

In Latin, the word “Remora” means “delay” which refers to the supposed abilities of remora fishes to slow down ships. The generic name of Remora is “Echeneis” which is derived from the Greek word “echein” meaning “to hold” and “naus” which means “ship”. So remora fish is the fish which stops ships.

A remora (often called suckerfish or sharksucker) is a brown-colored perch-like fish, elongated in shape. Remora fishes can be 30 to 110 cm (or 12 to 43 inches) long, depending on the species.

Remora fish and sharks can be usually found around each other as remoras often stick themselves to the sides of fishes like sharks, turtles, manta rays, whales, and other larger species of fishes and sea creatures. For the purpose of attaching, the texture of the host’s skin or shells does not matter. 

Remoras do not harm their hosts but simply attach themselves to their hosts and use them as a taxi to travel through water. Remoras also feed on food that falls off from the mouths of their hosts. In return for these favors, remoras rid their hosts (or taxis) from other parasites. The hosts also protect remoras from other predators.

This article will give you detailed information on Remora fishes classification, the special relationship between shark and remora, how remora head is used as a suction cup, and few other interesting facts about this fish.

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Classification of Remora Fish 

A remora fish belongs to the Echeneidae family and researchers have found 8 different species in this family which are further divided into 3 different taxonomic genera. The details of common remora fish are outlined below:

• Kingdom - Animalia (animals)

• Phylum - Chordata (chordates)

• Subphylum - Vertebrata (vertebrates)

• Superclass - Gnathostomata (Jawed vertebrates)

• Class - Actinopterygii (ray-finned fishes)

• Order - Perciformes (perch-like fishes)

• Family - Echeneidae

• Genus - remora

• Species - Common remora, live sharksucker, whalesucker, spearfish remora, marlin sucker, white suckerfish, slender suckerfish, and Echeneis neucratoides.

• Biogeographic regions - Atlantic oceans, Indian ocean, Pacific ocean

• Habitat - Found Worldwide in tropical and warm waters.

• Diet - Carnivorous 

Striking Features of Remora Fishes 

A remora fish is short and thick-set with 28 to 37 long and slender gill-rankers, 21 to 27 dorsal-fin rays, 20 to 24 anal fin rays, and 25 to 32 pectoral-fin rays. The most distinguishing feature of a remora fish is the suction cup attached atop the remora head. So let us find out some basic and some interesting facts about this fish.

• A remora fish is brown or black in color.

• The average length of remora fishes is 18 (30 to 40 cm) inches, but a few larger varieties can measure up to 2 feet in length.

• An adult remora has a weight of around 2 lbs.

• It has a long and flattened head and is about 26 to 29 % of its standard length.

• Remora fishes have smooth bodies and have small cycloid scales on their bodies.

• Remoras eat stray bits of food that sharks leave, and they also feed on tiny parasites (shrimp-like) that are present on the skin of sharks.

• These fishes have a rounded disc on their heads which have flexible membranes to maintain suction. They use this disc to obtain rides from other sea creatures. This sucking disc is developed from a modified spinous dorsal fin having 16 to 20 transverse movable lamina. These laminae create a partial vacuum to obtain suction capabilities. This disc structure is around 34 to 42% of its standard length.

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• These suction discs on Remora’s head have elastic collagen fibers that enable it to have maximum contact with the other fishes.

• Remora fishes do not have a swim bladder. 

• The lower jaw of a remora fish projects past its upper jaw. Its teeth are located in jaws, and the teeth are sharply pointed and are recurved slightly inward.

• Unattached remoras can be a nuisance to divers. Remoras tend to attach to anything large, and moving and divers seem to fit this category. That is why remoras attach themselves often to a diverse tank or body. If the diver is covered in a wetsuit, then remoras cannot be harmful to them. The encounter of a diver and remora fish is mostly comical since the fish tries to suck onto the trunk and limbs of divers. But if a remora gets attached to the skin of a diver directly, then the skin might get scraped.

• One can scare away a remora fish by purging a scuba diving regulator alternate air source on the fish’s face.

• If a remora fish is unable to get a ride (which allows swift movement of water over the gills of the fish), it could perish very quickly.

• A baby remora is not born with a fully formed suction cup on its head. They have to wait until they grow up to have that adhesive quality on their heads. During the baby’s development 3 typical fin elements i.e. the distal radials, fin spines, and the proximal, middle radials, go through a series of small changes to form the remora fish’s sucker.

• Remora shares its genetics with several other groups of fish. Mahi Mahi, cobia, jack, etc., are close relatives of remora fish. Cobia looks a lot like remora, but they do not possess the suction cup. They are similar to remora because they also swim alongside predators to scavenge from the food scraps of the predator.

• Remoras do not actively choose their habitats. They generally attach themselves to a host and then ride along to wherever the host takes them. Remoras can be found all around the world in temperate and tropical seas. They can be found both in coastal regions as well as far offshore.

• Remoras are carnivores and eat food scraps hunted by other animals, parasites attached to their hosts, and plankton. Most of the remoras’ meals come through its association with its host.

• There is not much information about how remoras reproduce and their larval production. Researchers have found adult remora pairs attached to the same host, but not much knowledge has been gained around their specific breeding behaviors. However, it is believed that they reproduce by spawning. Spawning is when a female release the eggs, and then a male fertilizes that egg outside of the body.

• Few fishermen use a remora fish to catch other larger fishes and turtles. They do so by attaching a line to the tail of a remora fish and then releasing the remora. Since a remora would soon attach itself to a host, the fishermen later carefully pull in both remora fish and the host.

The Special Relationship of Remora Fish and Shark 

Relationships get formed all over the animal kingdom, and the relationship between shark and remora is one such unlikely pair.

If you have seen documentaries about sharks or have had a chance to watch sharks in the water, you might have noticed the smaller companions of these sharks, which is the remora fish. Shark and remora share a symbiotic relationship which means that both benefit from their association. Remoras get an easy mode of transportation by attaching themselves to sharks and gain protection by being attached to a bigger animal. Remoras also get most of their food from sharks when the sharks drop off scraps of prey. In return, the remoras eat off parasites that accumulate on the shark’s skins and mouth. This way, the shark is benefited since these parasites would otherwise cause damage to the shark’s health and irritate the shark. Remoras also help in keeping the water around sharks clear of scraps which prevents the development of unhealthy and harmful organisms around its host shark. 

Studies show that shark species seem to understand the beneficial effects of having remoras in its life and how crucial a remora fish is to the shark’s well-being. This is demonstrated by a change in the behavior of a shark in the presence of remoras. It has been observed that a shark slows down (at the cost of even risking its own survival) so that remoras could attach themselves to the shark's body.

Though most shark species are happy with the symbiotic relationship they share with sharks, a few types of sharks are not happy with remoras. For example, it has been documented that lemon sharks and sandbars act aggressively with remoras, and at times they even consume the beneficial remoras. However, irrespective of these rare instances, the relationship of remora fish and shark is one of the most steadfast relationships in the ocean and is most likely to remain so for millions of years to come.

Details of Remora’s Suction Plate 

The origin of the adhesive disc on remora’s head is traced back to the mid to late Eocene period, approximately 56 to 39 billion years ago. This disc evolved from various components of the dorsal fin by many key transformations.

The most notable modification took place when the disc was situated in a postcranial position when the fin spines developed into laterally expanded lamelle. At this stage of development, the lamellae were still joined along the fish’s midline, similar to the dorsal fin spines found in generalized percomorphs. 

In the second stage, the disc migrated to the anterior position and the lamallele separated into paired ossification. Along with this, there was the development of pectination by the side of posterior margins of the lamellae, and the number of segments in the disc also increased.

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After acquiring the disc, there were further small scale modifications in some of the remoras, for example, the development of spinulas which enhanced their adhesion and grasping power. A remora that is attached to its host is subjected to dragging forces due to its fast-moving host, which needs a lot of resistance. But studies in fluid dynamics revealed that remoras shape evolved to streamline shape, which minimizes the dragging forces.

The remora’s adhesive disc has impressed scientists so much that they have designed an artificial one based on the same fundamentals. The oval-shaped disc of a remora fish can attach to many kinds of surfaces and has the potential for a lot of application. The fibres of remora’s suction cup are very flexible, which aids in even uneven surfaces and maintains a tight seal. Amongst a multitude of technological uses of such equipment, a few of them are:

• By equipping the bio-inspired device with electronics, it can be used to tag marine animals like whales, tunas, and sharks. This is deemed to be a non-invasive and reliable way for marine monitoring. These tags could travel through the world's oceans when attached to these fishes and help the scientists understand their spawning area, migration pattern, etc.

• They can be used for deep ocean studies.

• They can be a means of attaching tools or lights to the underwater surfaces of ships or bridges.