Arxiu d'etiquetes: abyssal fish adaptations

Animal mimicry: now you see me…

What do you see in the picture above? Maybe snakes… or maybe not? All animals try to enhance their survival rates, and one of the most effective ways to achieve this goal is by looking similar to some environmental elements, either by camouflaging or by imitating traits from other organisms. Mimicry is a complex and surprisingly phenomenon present in almost every animal taxa acting as an evolutionary driving force. Do you know what types of mimicry exist and which animals do perform each one? Are you ready to read more about this topic? If that’s the case, keep reading!

Mimicry vs camouflage (or crypsis)

The word mimicry (that derives from the Greek term mimetikos = “imitation”) was firstly being used to describe people who have the ability to imitate. From 1851 on, its use extended to other life forms.

Sometimes, the term mimicry is used as a synonym of “camouflage or crypsis”. Although these two words are sometimes confused and used equally, from a biological point of view they are well differentiated terms:

  • Mimicry: the ability an organism develops to imitate one or more traits from another organism (with which it’s unrelated) so that it can obtain some benefit.
  • Camouflage (or crypsis, from the Greek word kryptos = “hidden”): the ability an organism has to be unnoticed by its predators (or prays) by copying some environmental traits or by developing a disruptive coloration that allows it to hide.

Some authors consider that camouflage includes only to the ability an animal has for imitating morphological traits from some environmental elements, such as different natural surfaces, plants or even sessile animals (i.e. immobile animals) like corals and sponges (as you can see on the picture below). On the other hand, mimetic animals go further and try to imitate not only morphological traits, but physiological and behavioral, looking for a response from other animals.

Can you see the camouflaged seahorse? (Picture by Stephen Childs, CC).

To sum up: the main objective of mimetic animals is to trick the senses (e.g. sight, hearing, smell…) of the other organisms they live with, in order to induce them a specific behavior that gives mimetic animals a benefit in return.

Types of mimicry

There are different ways to classify the different types of mimicry, but I will show you two main groups of mimicry, in which we will see different subtypes: defensive mimicry and non-defensive mimicry.

Defensive mimicry

The defensive mimicry is specially performed by animals that have lots of predators, so their survival rates depend on avoiding their predators.


Venomous and poisonous animals tend to develop flashy traits (especially flashy morphological traits, like coloration and menacing sounds) which alert other animals about their danger. This phenomenon is known as aposematism (when an animal has a flashy coloration we talk about aposematic coloration). In the Batesian mimicry, the mimetic organism (that is usually harmless and edible) copies the flashy traits of a venomous or poisonous organism present in its habitat in order to make predators think it’s a harmful species. Thus, the mimetic organism avoids being caught and eaten by predators.

Poisonous Coral Snake (on the left) and non-poisonous Scarlet King Snake or False Coral Snake (on the right). The second one imitates the aposematic coloration of the first one (Source:



Sometimes, there are various poisonous or venomous species coexisting at the same time in the same habitat that are all being very hunted by predators (and sometimes by the same predator). In some of these cases, even when only one of these species has an aposematic trait to dispel predators, the rest of them try to mimic it and develop this trait (or traits). In contrast with de Batesian mimicry, in this model all species are harmful at some degree.

Try to think that all these species finally develop the same aposematic coloration: when predators prey on one of these species and are harmed in result, probably they won’t attack again any species that has the same coloration pattern. Thus, predation pressure will be distributed within the species matrix.

Different geographical forms of both Heliconius erato (top row) and Heliconius melpomene (bottom row). Heliconius melpomene is a widespread neotropical species well known for its geographic diversity in color pattern. Throughout its range, H. melpomene is co-mimetic with Heliconius erato (which is generally less abundant than H. erato). Both have a disgusting flavor when being eaten (source:



This is an unusual type of mimicry (only a few cases in snakes are known), and it occurs when a harmful species copies an aposematic trait (e.g. coloration) of a less dangerous organism. What could this mechanism be useful for?

Mimetisme_angIn the picture above, we can see that predators that feed on a harmful organism die (e.g. because it’s poisonous), so that the information “this animal is poisonous and mortal, don’t eat it!” won’t be transmitted to the rest of the predator population nor the next generations of predators. Thus, this harmful prey will remain preyed by predators. On the other hand, predators that feed on a less harmful prey and stay alive will have the chance to transmit this information to the rest of the population, so that predators will stop feeding on this prey.

In light of this situation, what do the most harmful organisms do? they try to imitate the aposematic traits of less harmful organisms (like coloration or shape) so that predators that feed on these less harmful organisms and stay alive, learn that all organisms with the same traits are dangerous. So, the predation pressure will fall for all preys.

Non-defensive mimicry

One of the most important types of mimicry within the non-defensive mimicry is the Peckhammian mimicry.


Unlike defensive mimicry, in this case are predators (or parasites) the ones that develop the traits of a more or less harmless species (or even of a beneficial one) in order to be unnoticed by their preys or hostages.

Plagiotremus rhinorhynchos (on the right) is an aggressive mimetic species that imitates another fish known as Laborides dimidiatus or bluestreak cleaner wrasse. Plagiotremus rhinorhynchos (family Blenniidae) imitates youth specimens of Labroides dimidiatus (family Labridae) both morphologically and behaviorally. Many species of fishes enter corals in order to be cleaned from parasites by Labroides dimidiatus. Taking advantage of this situation, P. rhinorhynchos get close to these coral fishes by mimicking the bluestreak cleaner wrasse in order to feed on their tissues (Pictures: the left one by Karelj, CC  and the right one by JennyHuang, CC).

Aggressive mimicry can be confused with some camouflage or crypsis mechanisms, as sometimes these two terms can be overlapped or maybe show no evident differences. This is the case of some abyssal fish species which have one or more filaments of their dorsal fins transformed into lures (sometimes these lures are bioluminescent). These lures sometimes mimic the shape of the abyssal fish’s preys, so those preys feel strongly attracted by them. Some authors propose that preys could be the model organisms and that abyssal fishes would modified their dorsal fin through an evolutionary process.

Abyssal fish on a photogram from the film ‘Finding Nemo’ (© Pixar, 2003).
Abyssal fish…a way more real than the one showed above (with its luminescent lure) (Image source:

A curious case: the automimicry

The automimicry (also known as intraspecific mimicry) is a special case of mimicry that takes place when an organism transforms some part of its body in order to seems like another part of its own body or even of the body of another member of its species (e.g. a male that mimics a trait from females). The objectives of this type of mimicry are to obtain some benefit from other organisms or maybe to be unnoticed by their predators or preys.

The northern pygmy owl (Glaucidium californicum) has two big dark spots behind its head which remind of two big eyes (picture by Michael Durham).

Mimicry makes animals to evolve!

Mimicry is one of the processes that makes animals to evolve faster (do you want to learn more about evolutionary processes? Enter this link!).

These changes may occur in a higher or lower speed. So, what about those animals that mimic other organisms? Mimetic animals are in constant selective pressure to look more like their models in order to go unnoticed and improve their survival, but at the same time imitated organisms (the models) are also under selection to sharp their ability to discern between models and imitators.

.            .             .

Thus, mimicry is an incredible evolutionary engine: a perpetual struggle between mimetic organisms and imitated ones in order to improve their respective survivals.


  • Bone Q., More R. Biology of fishes. 3a ed. Taylor & Francis.
  • Campbell, N.A., Reece J. B. 2007. Biología. Ed. Médica Panamericana.
  • Cheneya K.L., N. Justin M. 2009. Mimicry in coral reef fish: how accurate is this deception in terms of color and luminance?. Behavoural ecology, Oxford Journals. Vol 20. P. 459-468.
  • Harper D. Online Etymology Dictionary.
  • Kashyap H. V. 2001. Advanced Topics In Zoology. Ed. Orient Blackswan.
  • Sarmiento O.F., Vera F., Juncosa E. J. 2000. Diccionario de ecología: paisajes, conservación y desarrollo sustentable para Latinoamérica. Ed. Abya Yala.

Main picture source:


Voyage to the bottom of the deep sea (II): Biodiversity in the deep sea

This week we are continuing our voyage to the bottom of the deep sea. While last week we focused on the adaptations that fishes have suffered, this week we are focussing on the biodiversity. In concrete, we are explaining crustaceans, squids, cnidarians (corals, jellyfishes and anemones), fishes and worms. 


In 1840, the scientist Edward Forbes concluded that there wasn’t life under 550 meters depth. Nowadays, it is known that this is not true because recently it has been found a fish at 8,100 meters. It has been determined that the relative abundance of animals depends on depth. In fact, in general terms, the abundance decreases with depth, but this don’t exclude that there are a lot of species.




Amphipods are by far the most abundant crustaceans in the deep sea. They are small animals with the body compressed laterally and without a carapace, which feeds on carrion and live inside cavities made by themselves in the sea floor. These small animals are transparent, except for them eyes, which are red due to a pigment in the retina.

amphipode-abysseDeep sea amphipod. They are characterized by the presence of a transparent body with red eyes. (Picture from

Other deep sea crustaceans are stone crabs, with a carapace of 7.5 cm length and legs of about 15 cm; the armoured shrimp, one of the species that lives at 6,000 meters and has a length of 7 to 10 cm; and more.


In spite of the general thinking that deep sea squids are all large, like the giant squid, which can achieve a length of 18 meters; the truth is that this is an exemption because there are some spices of just 4 cm. They hunt with the suckers in the tentacles and driving the prey to the mouth. Most of these squids are bioluminescent and can regulate the colour, the intensity and the angular distribution of the light.

The Humboldt or jumbo squid (Dosidicus gigas) lives in the western coasts of Central and South Amercia and can achieve a length of 4 meters, which feeds on fishes and practise cannibalism.

Dosidicus_gigasHumboldt or jumbo squid (Dosidicus gigas). They have bad reputation because they attack divers.


Differences between shallower cnidarians and deep ones are due to differences in the food distribution. In the deep sea, anemones and corals don’t have directly phytoplankton and zooplankton, and they depend on the nutrient rain from the shallower waters of the ocean. On the other hand, jellyfishes have a slow metabolism to survive in hard conditions. It supposes slower growth, but a longer life.

To give an example, this crown jellyfish inhabits between 200 and 2000 meters depth and can measure until 15 cm. It feeds on small crustaceans and organic matter. Its red colour let them be camouflaged in the environment. In addition, they are bioluminescent animals.

Atolla wyvillei[3]Crown jellyfish. Its red colour let them be camouflaged in the environment.

Deep-sea jellyfishes are voracious predators, but also can be a prey for some fishes. They produce light discharges to attract small animals. To dissuade predators, they expel a brilliant particles stream.

An habitual feature of deep-sea jellyfishes, but also present in other groups, is gigantism. It means they are bigger than their equivalents in the shallow ocean. The possible explanation to this could be that bigger animals are more efficient than smaller to get food when the environmental conditions are almost constant during long periods of time.


Gonostomatidae fishes are the most abundant vertebrates in the Earth and live in the mesopelagic zone. Together with the lantern fishes, they represent a 90% of the captures in the pelagic trawling fishery. Deep-sea fishes usually have a length between 2,5 – 10 cm and a thin and soft body, but there are exceptions.

There are some examples here:

  • Anglerfish: These fishes inhabit in the deepest parts of the oceans and present the optimal colouration to absorb the few light that arrive and, in this way, to be camouflaged. They present a light in the end of the antenna, which let them to capture preys.
  • Spiny lantern fish: Because of its silvery body, this fish is not much vulnerable since its contour can’t be seen clearly. In addition, spiny lantern fish presents a bag in the eye with bioluminescent bacteria.
Pez linterna espinoso
Spiny lantern fish
  • Pelican eel: This animal can measure 2 meters long. Its enormous mouth are connected directly to the stomach.
Pelican eel
Pelican eel
  • Tripodfish: Tripodfish has long prolongations in its pelvic and caudal fins, which let them put on the sea floor, while it is waiting for its prey.
  • Black swallower: This small fish has the ability to dilate a lot its stomach and, in this way, it can swallow preys bigger than itself.
Black swallower
Black swallower



Deep-sea worms can be from microscopic to measure 2 meters long and are one of the most abundant and different invertebrates. They can be of different groups: polychaetes, tubular worms, sipunculids and equiurids. They live partly or totally buried in the sediments.

Tubular worms usually live in big groups near to thermal springs and present red bright gills as a consequence of a high level in hemoglobin to absorb oxygen. In addition, they can retain sulfurs, which will be used for symbiotic bacteria.

Riftia_fish_EPR_Kristof_Lutz-pTubular worms. They use the sulphur produce in the thermal springs thanks to symbiotic bacteria.

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Voyage to the bottom of the deep sea (I): Adaptations to deep sea life

The publication of this week is a voyage to the bottom of the deep sea; where there are life in forms we aren’t generally used to. This post will be divided in two parts: in the first part we are talking about the adaptations and in the second part about some examples of the biodiversity. 


Till recently, the maximum depth where fishes have been seen was about 7,700 meters, but a research of the University of Hawaii has overtake it. Now, the maximum depth is about 8,143 meters, in the Mariana Trench. This value is close to the theoretic limit of 8,200 meters that some scientist have calculated as the maximum depth where a fish can live. In this video you can see the fish, which is eel-like, while, translucent and blind:


Deep-sea animals have developed a group of adaptations due to the lack of light, the extremely high pressures and a low temperature of the water (near to 4ºC).

Sense organs 

Most of them have developed very sensitive eyes, despite living in the darkness, to sense the bioluminescent animals and the environmental light coming from the surface. The eyes are tubular, which consist on a multi-layer retina and a big lens, what allows them to detect the maximum quantity of light in one direction. Some species have secondary lens in the laterals and a bigger lens to improve lateral vision. Other can distinguish between environmental and bioluminescent light thanks to a filters.


Some species have specialized the olfactory sense to detect preys and other fellows.

Like other fish species, to detect the vibrations in the water, they present the lateral line system, though this system can be complemented, in some species, by complementary sense organs coming from the modification of the fins.


The colour of the deep-sea animals is a response to the necessity of become camouflaged of the predators and to take advantage of the environmental light. These animals usually have either a red or orange coloration to be camouflaged in the blue environmental light; or silvery to avoid the predators could see perfectly its outline; or colourless and transparent.


The shape of the deep-sea fishes is very different from those who live in the sea surface. They don’t usually have hydrodynamic shapes because they spend almost all the time suspended in the water waiting for a prey. They present big mouths with sharp teeth. Some fishes have long bodies, what has been associated for the necessity of enlarge the lateral line system to increase the sensitivity to detect preys. Other have globular shapes, like frogfishes; laterally compressed bodies…

pez-pescador--644x362Humpback anglerfish has a globular shape and bait appendix in the head to attract its preys.


Bioluminescence is the capacity for producing light without heat thanks to the protein luciferin in the presence of oxygen and the luciferase, normally inside of a specialized organ called photophore. However, there are some species that accumulates bioluminescent bacteria inside the photophore. Other present a gland that expel a bioluminescent fluid to distract predators. These animals use this capability to attract preys, distract predators and to communicate with fellows.

Photostomias2This fish has a photophore in the later part of the eye.

Some fishes can produce red light, so, they can see them preys without being seen. 


Food of deep-sea species can be of three types:

  • Big pieces: living preys and dead animals.
  • Particles coming from the surface, smaller and less nutritive.
  • Dissolved nutrients.

Benthic species (those which live on the sediment) depend on the accumulation of organic particles in the sea floor or on the organisms that lives in the upper part of the sediment, while pelagic ones (those which stay in the water column) are predators.

Predators usually have a bioluminescent bait, which is a illuminated prolongation that they use near to the mouth to attract preys. In addition, many ones can expand the jaws to swallow the whole animal.


To overcome the difficulty in finding a partner in the deep-sea is so big that they have developed different strategies: to produce light, sounds or pheromones to attract the partner; to be hermaphrodite; or to maintain long relationships.

An example of this last case are anglerfishes. Females grows till a length of 35 cm (without the fishing line), despite their ovaries are inactive; while males are tiny. Females produce pheromones to attract males and then they combine their veins and this stimulates gonads and finally the eggs are fertilized. Finally, the male’s body become a testis mass.

The fact that deep waters are more stable than shallow waters suppose an advantage: they lay less eggs, but they are bigger, have a shorter larvae life and survive almost all.

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