Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Such migrations are usually done for better feeding or to reproduce, but in other cases the reasons are unclear.
The European eel is a species of eel, a snake-like, catadromous fish. They are critically endangered due to overfishing by fisheries on coasts for human consumption and parasites.
The American eel is a facultative catadromous fish found on the eastern coast of North America. Freshwater eels are fish belonging to the elopomorph superorder, a group of phylogenetically ancient teleosts. The American eel has a slender, supple, snake-like body that is covered with a mucus layer, which makes the eel appear to be naked and slimy despite the presence of minute scales. A long dorsal fin runs from the middle of the back and is continuous with a similar ventral fin. Pelvic fins are absent, and relatively small pectoral fins can be found near the midline, followed by the head and gill covers. Variations exist in coloration, from olive green, brown shading to greenish-yellow and light gray or white on the belly. Eels from clear water are often lighter than those from dark, tannic acid streams.
Eels are any of several long, thin, bony fishes of the order Anguilliformes. They have a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was a mystery for a very long period of scientific history that continues into the present day. Of significant interest is the search for the spawning grounds for the various species of eels and identifying impacts to population decline in each stage of the life cycle.
The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. The word abyss comes from the Greek word ἄβυσσος (ábussos), meaning "bottomless". At depths of 4,000–6,000 m (13,000–20,000 ft), this zone remains in perpetual darkness. It covers 83% of the total area of the ocean and 60% of Earth's surface. The abyssal zone has temperatures around 2–3 °C (36–37 °F) through the large majority of its mass. The water pressure can reach up to 76 MPa.
The Anguillidae are a family of ray-finned fish that contains the freshwater eels. Eighteen of the 19 extant species and six subspecies in this family are in the genus Anguilla, and all are elongated fish of snake-like bodies, with long dorsal, caudal and anal fins forming a continuous fringe. They are catadromous, spending their adult lives in freshwater, but migrating to the ocean to spawn.
Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs.
Snipe eels are a family, Nemichthyidae, of eels that consists of nine species in three genera. They are pelagic fishes, found in every ocean, mostly at depths of 300–600 m (980–1,970 ft) but sometimes as deep as 4,000 m (13,000 ft). Depending on the species, adults may reach 1–2 m (39–79 in) in length, yet they weigh only 80–400 g (2.8–14.1 oz). They are distinguished by their very slender jaws that separate toward the tips as the upper jaw curves upward. The jaws appear similar to the beak of the bird called the snipe. Snipe eels are oviparous, and the juveniles, called Leptocephali, do not resemble the adults but have oval, leaf-shaped and transparent bodies. Different species of snipe eel have different shapes, sizes and colors. The similarly named bobtail snipe eel is actually in a different family and represented by two species, the black Cyema atrum and the bright red Neocyema erythrosoma.
The Atlantic tarpon is a ray-finned fish that inhabits coastal waters, estuaries, lagoons, and rivers. It is also known as the silver king. It is found in the Atlantic Ocean, typically in tropical and subtropical regions, though it has been reported as far north as Nova Scotia and the Atlantic coast of southern France, and as far south as Argentina. As with all elopiformes, it spawns at sea. Its diet includes small fish and crustaceans.
The Japanese eel is a species of anguillid eel found in Japan, Korea, Taiwan, China, and Vietnam, as well as the northern Philippines. There are three main species under the Anguilla genus, and all three share very similar characteristics. These species are so similar that it is believed that they spawned from the same species and then experienced a separation due to different environments in the ocean. Like all the eels of the genus Anguilla and the family Anguillidae, it is catadromous, meaning it spawns in the sea but lives parts of its life in freshwater. Raised in aquaculture ponds in most countries, the Japanese eel makes up 95% of the commercially sold eel in Japan, the other 5% is shipped over by air to the country from Europe. This food in Japan is called unagi; they are an essential part of the food culture, with many restaurants serving grilled eel called kabayaki. However, presumably due to a combination of overfishing and habitat loss or changing water conditions in the ocean interfering with spawning and the transport of their leptocephali this species is endangered.
The small-spotted catshark, also known as the sandy dogfish, lesser-spotted dogfish, rough-hound or morgay, is a catshark of the family Scyliorhinidae. It is found on the continental shelves and the uppermost continental slopes off the coasts of Norway and the British Isles south to Senegal and in the Mediterranean, between latitudes 63° N and 12° N. It can grow up to a length of 1 m, and it can weigh more than 2 kg (4.4 lb). It is found primarily over sandy, gravelly, or muddy bottoms from depths of a few metres down to 400 m (1,300 ft). S. canicula is one of the most abundant elasmobranchs in the northeast Atlantic and Mediterranean Sea. The majority of the populations are stable in most areas.
The giant mottled eel, also known as the marbled eel, is a species of tropical anguillid eel that is found in the Indo-Pacific and adjacent freshwater habitats.
The European conger is a species of conger of the family Congridae. It is the heaviest eel in the world and native to the northeast Atlantic, including the Mediterranean Sea.
Natal homing, or natal philopatry, is the homing process by which some adult animals that have migrated away from their juvenile habitats return back to their birthplace to reproduce. This process is primarily used by aquatic animals such as sea turtles and salmon, although some migratory birds and mammals also practice similar reproductive behaviors. Scientists believe that the main cues used by the animals are geomagnetic imprinting and olfactory cues. The benefits of returning to the precise location of an animal's birth may be largely associated with its safety and suitability as a breeding ground. When seabirds like the Atlantic puffin return to their natal breeding colony, which are mostly on islands, they are assured of a suitable climate and a sufficient lack of land-based predators.
Acipenser oxyrinchus is a species of sturgeon.
The Mediterranean moray, also known as Roman eel, is a species of fish in the moray eel family. It has a long eel-like body and is found in the eastern Atlantic Ocean and Mediterranean Sea. Its bite can be dangerous to humans.
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, to spawn refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquatic mammals and reptiles, reproduce through the process of spawning.
Eels are ray-finned fish belonging to the order Anguilliformes, which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators.
Coastal fish, also called inshore fish or neritic fish, inhabit the sea between the shoreline and the edge of the continental shelf. Since the continental shelf is usually less than 200 metres (660 ft) deep, it follows that pelagic coastal fish are generally epipelagic fish, inhabiting the sunlit epipelagic zone. Coastal fish can be contrasted with oceanic fish or offshore fish, which inhabit the deep seas beyond the continental shelves.
Fish go through various life stages between fertilization and adulthood. The life of a fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac which provides stored nutrition. Before the yolk sac completely disappears, the young fish must mature enough to be able to forage independently. When they have developed to the point where they are capable of feeding by themselves, the fish are called fry. When, in addition, they have developed scales and working fins, the transition to a juvenile fish is complete and it is called a fingerling, so called as they are typically about the size of human fingers. The juvenile stage lasts until the fish is fully grown, sexually mature and interacting with other adult fish.
Feagans-Bartow, J. (2014). Ecology of the oceanic rim: pelagic eels as key ecosystem components. Marine Ecology Progress Series, 502, 257–266. https://doi.org/10.3354/meps10707
