Tuesday, March 29, 2011

Remora: Not Quite a Drag


Remora are a group of fish that are members of the family Echineidae; there are eight known species, all belonging to one of four genera: Echineis, Phtheirichthys, Remora, and Remorina [4]. They are usually found in warm, southerly waters. Remora interact with a wide range of marine animals. They are known to attach themselves to fish (particularly sharks and rays) and whales, along with other large marine animals – and even the occasional snorkeler or scuba diver [2]. Remora possess a modified dorsal fin that runs from just above the snout of the fish to the nape of its neck. This fin has several transverse plates; it is used by the remora to attach itself to its host. Some remora cling to the host’s torso, but others are found on or near the host’s gills. The name “remora” is the Latin word for “delay”; they were believed to slow down ships and animals that they clung to because of the weight they add and the drag they produce.


Description of the Relationship:

Unfortunately, very little is known about the origin of remora and the evolution of their unique trait and behavior. While other fish – such as the “cleaner fish” studied earlier in the semester – exist in a relationship that superficially resembles the one between a remora and its host, no other identical examples are known.

Depending on the type of remora and the host, the relationship can be either mutualistic or commensal. Most often the relationship is commensal – the remora attach themselves to a host and travel on it, gaining transport, protection from predators, and food. This relationship is commensal when the remora eats scraps left behind by the host or other debris it is exposed to in the host’s travels, but can become mutualistic if the remora is of a variety that eats dead skin and bacteria from the host’s body [1]. In either case the remora benefits from the relationship, while the host either is unharmed or actively benefits along with the remora; for this reason it is impossible to definitively categorize the remora/host relationship as either mutualistic or commensal.


Cost/Benefit Analysis:

Whether the relationship is commensal or mutualistic, in nature there is little or no harm to the host. In commensal cases, it has an unexpected passenger that does not seek to harm it and that will, at worst, either slow it down by increasing drag on the host as it swims or perhaps cause some minor gill irritation. In mutualistic cases, the host benefits as the remora cleans its host of dead skin, bacteria, and ectoparasites.

Similarly, the remora always benefits from this relationship in a natural environment. Whether the relationship is commensal or mutualistic it gains food, shelter, and protection. Since the remora can detach itself from its host, and is capable of swimming freely, its well-being is not linked to that of the host [2]. Some scientists hypothesize that remora run the risk of being eaten by their hosts, but to date no evidence has been found supporting this idea.

This relationship has incurred some harm for both the remora and their hosts in cases where they live in a human-populated environment due to an unusual fishing practice of some aboriginal tribes. In some regions where remora are prevalent, fisherman use a live remora tied with a long cord in lieu of a fishing hook and rod – they wait until a game fish is spotted, release the remora, allow it to attach itself to the game fish, and then haul both back in with the rope. In some regions the un fortunate remora is eaten along with the game fish, but in other areas they are honored for their contribution to the tribe’s well-being [2]. Despite the man-made disadvantage, the relationship persists because it provides remora with ready food and the high-speed motion they need to keep their gills functioning [2].


Remora in Action: http://www.youtube.com/watch?v=9z3pqp12UEg


[1] http://www.britannica.com/EBchecked/topic/497706/remora

[2] http://animaldiversity.ummz.umich.edu/site/accounts/information/Remora_remora.html

[3] http://www.gma.org/fogm/Echeneis_naucrates.htm

[4] http://en.wikipedia.org/wiki/Remora


  1. From what I can tell, it seems that multiple remoras can inhabit a single organism. I can understand how this is a benefit for the remora, but what about the other organism? You mention that they add weight and drag, which probably negatively affects predatory skills or makes them more vulnerable. Also, the organisms that want to be cleaned could possibly find other means to do so. One of the overarching themes that has been a part of this class is that of natural selection. Why has natural selection not selected for organisms to not allow too many remoras to travel with them?

  2. The relationship the remora has with other organisms reminds me of the example in our reading where the mites attached themselves to the legs of a beetle and used them for transportation. You also mentioned the example of the cleaner fish. The difference between the cleaner fish and the remora is that the clients of the cleaner have a sort of "trust" for the cleaner and allow them to approach after being advertised to. And in the case of the beetle, it has no way of ridding itself of the mites (or perhaps it can't see them.) Either way, its curious to me that a shark, say, would let a remora (which I would think would be something a shark might eat) approach and hang around without attacking it. I'm wondering if you read anything or have any ideas about how the remora can approach and attach to a potential predator. (Is there an "understanding" between them or do they go undetected, etc.?)

  3. I understand the relationship between the two organisms. It is similar to many examples discussed in class. It is somewhat different from the cleaner fish such that the remora increases drag and slows the fish down. Does the remora approach the partner in any particular way? The cleaner fish had mimics that would harm the partner instead.. Does the remora have fishes that mimic its nature? Also you mentioned that remora is honored for their contribution in helping fishermen catch fishes.. how do they honor them?