Arxiu d'etiquetes: basking shark

Large sharks that eat plankton

Baleen whales are known to be the biggest animals on Earth that feed on plankton, but they are not the only big animals that eat these tiny organisms. In this post, you will discover three species of shark that consume plankton. 


Plankton refers to those tiny organisms that drift in the water with the currents. They can be classified as phytoplankton, which include the planktonic algae and other autotrophs or producers that may be the most important producers in many marine ecosystems, or as zooplankton, which include the heterotrophic plankton (the primary consumers). There are so many groups of organisms that spend all their life in the plankton, but other may be present just in some phases.

Organisms included in the zooplankton (Picture: Sci-news).
Organisms included in the zooplankton (Picture: Sci-news).

So many marine groups of animals feed on plankton, but baleen whales are known to be among the biggest animals that eat these small creatures. Some sharks are known to eat these little organisms: the famous Whale shark (Rhincodon typus), the awesome Basking shark (Cetorhinus maximus) and the stunning Megamouth shark (Megachasma pelagios). Did you know about these three species of planktophagous sharks? 


The biggest fish in the world usually is 12 meters long (but may achieve a length of 15 meters), weights 22 tonnes and its mouth is so wide that could swallow a car. We are referring to the famous whale shark (Rhincodon typus).

Whale sharks are true sharks, so they breathe using gills and are cold-blooded fishes. The reason of their name is the fact that they feed on plankton in a similar way of whales: they swim slowly (1,5-5 km per hour) with the mouth opened (which has dense filter screens) and swallow the small organisms present in the water, like coral and teleost spawn, krill, copepods, jellyfishes, small cephalopods and schooling fishes. They are also reported to feed almost vertically in the water. They can be identified so easily for their colossal size and for their dark blue colouration with white spots all over the body.

The whale shark is the biggest fish in the world (Picture: Mauricio Handler).
The whale shark (Rhincodon typus) is the biggest fish in the world (Picture: Mauricio Handler).

Little is known about the biology of these big animals. They live usually alone in coastal, pelagic and oceanic waters of the tropics and warm temperate zones, except the Mediterranean sea. They migrate extremely large distances. Every spring, they migrate to the continental shelf of the central west coast of Australia.

Due to direct and indirect fishing, their populations have reduced and the IUCN classifies them as a vulnerable species. Nowadays, their fishing is widely forbidden. Do you know that swimming with whale sharks has a negative impact on their populations? 


The world’s second largest fish is also a filter feeder and is also a shark: it is the basking shark (Cetorhinus maximus). This shark lives in coastal and pelagic of temperate and boreal waters, but is a migratory species.

They can be distinguished from other sharks for their big mouth, small teeth and long gill slits. They are solitary animals, but sometimes they can form a small group of animals. Basking sharks consume small fish, fish eggs and zooplankton. They capture them on their gill rakers with the help of mucus secreted in the pharynx. In average, they swim at 3,7 km per hour. So, how many tonnes of water filter per hour? 

The basking shark (Cetorhinus maximus) is the second biggest fish in the world (Picture: FLMNH).
The basking shark (Cetorhinus maximus) is the second biggest fish in the world (Picture: FLMNH).

Their conservation status is vulnerable, but is considered to be endangered in the North Pacific and the Northeast Atlantic subpopulations. The fact that their fins are among the most valuable in international trade explains their conservation status. Moreover, accidental fishing is a threat to consider.   In some regions, such us European Union, they are protected by law.


The megamouth shark (Megachasma pelagios) is a large oceanic shark (at least 5 metres long) with long pectoral fins, but sometimes is littoral on the continental shelves. They live in tropical and subtropical waters. Little is known about this species because it was discovered in 1976.

The megamouth shark (Megachasma pelagios) is a strange planktophagous shark (Picture: ).
The megamouth shark (Megachasma pelagios) is a strange planktophagous shark (Picture: Theethogram).
Its low-flow filter apparatus suggest it is less active than the whale and basking sharks. Megamouth might swim slowly with its jaws wide open to capture their preys by suction. A surprising feature of this shark is its bioluminescent mouth, which acts to attract prey. Its conservation status is unknown, but accidental fishing might be a threat.


  • Camhi, MD; Pikitch, EK & Babcock, EA (2008). Sharks of the Open Ocean: Biology, Fisheries & Conservation. Blackwell Publishing.
  • Carrier, JC; Musick, JA & Heithaus, MR (2010). Sharks and their relatives II: Biodiversity, adaptive physiology and conservation. CRC Press.
  • Castro, P & Huber ME (2003). Marine biology. The McGraw-Hill (4 ed).
  • Fundación Squalus (2011). Guía para la identificación de especies del Programa de avistamiento de tiburones y rayas de la Reserva de Biosfera SEAFLOWER.
  • IUCN: Cetorhinus maximus 
  • IUCN: Megachasma pelagios
  • IUCN: Rhincodon typus
  • National Geographic: Whale sharks 
  • Oceana (2008). Guía de los Elasmobranquios de Europa.


How do warm-blooded fishes maintain a constant temperature?

Last week, we saw the mechanisms of poikilotherm fishes (or cold-blooded fishes) to fight against high and low temperatures. This week I will talk about endotherm fishes (or warm-blooded fishes). 


99% of fishes are cold-blooded, it is that the body temperature is similar to water temperature. Since some weeks ago, it was known that tuna, the group of basking sharks and swordfishes are regionally warm-blooded animals. Now, it is known that, in addition to this regionally warm-blooded specie, opah is totally endotherm.

This warm-blooded fishes, either regionally or totally, have, in general, something in common: they are big predators of fast preys and their bodies are hydrodynamic.


Tuna and basking sharks have myoglobin-rich muscles (a blood pigment useful for the diffusion and storage of oxygen inside muscles), called red muscles, which are the responsible of swimming, which increase a lot temperature during this activity. Thanks to these muscles, this animals can constantly swim because they give the necessary energy. But, as they breathe through gills, it is necessary something more to maintain a constant temperature.

Tonyina (Thunnus) (Foto de Greenpeace).
Tuna (Thunnus) (Picture from Greenpeace).
Tauró peregrí () (Foto de Ocio en Galicia).
Basking shark (Cetorhinus maximus) (Picture from Ocio en Galicia).

This “something” is counter-current circulatory system of the blood. The red muscles are placed close to vertebral column. Longitudinal arteries and veins carry the blood for all the body and are placed en each side of the body under the skin. Longitudinal arteries branch in small arteries that go to red muscles. Blood move away of red muscles through veins that flow into longitudinal veins, and go to heart. It is called a counter-current circulation because arteries carry the blood to red muscles and veins move away blood from there. In fact, main arteries and veins divide into small crossed vessels, what is called a rete mirabile.

Sistema a contracorrent de la sang (Foto extreta d'aquí).
Counter-current circulation: (a) bluefin tuna and (b) basking shark (Picture from here).

This counter-current system allows that heat received in veins from red muscles is transferred into arteries that get in in them, instead of going to the periphery of the body and gills, where this heat would be lost to water. So, it allows to maintain the heat produced in red muscles.

Some species of tuna, like bluefin tuna, and of basking sharks, moreover, can maintain a high temperature in other parts of the body, like stomach and guts, brain and eyes. This organs are irrigated by a rete mirabile.


Swordfishes have two particularities that differ from the prior examples:

  1. They just heat the brain and ocular retina.
  2. They have heater tissues.

Heater tissues consist on an extraocular muscles, that in the past were the responsible of moving the eyes in all directions. Nowadays, they are not contractile, but maintain a lot of mitochondria, which are the responsible to produce heat. This heat is maintained in the head of the animal due to a counter-current circulation, allowing the warming of brain and retina.

Peix espasa (Xiphis gladius) (Foto de Bajo el Agua)
Swordfish (Xiphis gladius) (Picture from Bajo el Agua)


A study published in Science this May has revealed that opah (Lampris guttatus) is a totally warm-blooded animal. According to this study, body temperature of opah is 5ºC higher than sea temperature.

Peix lluna real (Lampris guttatus) (Foto de IdentidadGeek)
Opah (Lampris guttatus) (Picture from IdentidadGeek)

Most of this heat is produced in pectoral fin muscles, which are surrounded by a fat layer of 1 cm that acts as a thermal insulation. Despite of this, to maintain a high body temperature, they use their gills (like a radiator), in which there is a counter-current circulation of the blood. So, blood warmed in muscles of pectoral fins goes to gills to get oxygen, but avoid the loose of heat with a counter-current system.

Moreover, they have a secondary circuit that maintain the temperature in the brain and eyes.


  • Hickman, Roberts, Larson, l’Anson & Eisenhour (2006). Principios integrales de Zoología. McGraw Hill (13 ed).
  • Hill, Wyse & Anderson (2006). Fisiología animal. Editorial Medica Panamericana (1 ed)
  • Wegner, N; Snodgrass, O; Dewar, H & Hyde, JR (2015). Whole-body endothermy in a mesopelagic fish, the opah, Lampris guttatus. Science. Vol. 348 no. 6236 pp. 786-789, DOI: 10.1126/science.aaa8902