Catadromous Fish Migration Explained

Different types of fishes migrate, on the basis of their requirement, ranging from daily to annually, and the distance ranging from some meters to thousands of kilometers. They migrate usually in the search of food or to reproduce on the basis of their requirement but in some of the cases, the reasons are unclear. 

Here migration means the movement of the fish from one place to another on a larger scale and duration than those arising during normal activities. The particular types of migration that can be seen are anadromous migration (here adult fish live in the sea and they migrate into freshwater to spawn), and catadromous migration (in this adult fish live in freshwater and migrate into saltwater to spawn). 

(Image will be Uploaded Soon)

Marine forage is the fish, which makes larger migrations for their spawning, feeding, and nursery grounds. The movement of these species is directly related to ocean currents and the availability of food in the different areas at different stages of the year. The migration of fish is directly connected to the fact that the fish cannot identify their own offspring and moving this way prevents cannibalism (consuming another individual of the same species as food).  Some of the species have been described by the UNCLOS (United Nations Convention on the Law of the Sea) as highly migratory species.  These are large pelagic fish that move in and out of the exclusive economic zones of different nations, and these are covered differently in the treaty from other fish.

Classification of the Migratory Fishes 

Depending on the various aspects of fish life, scientists have developed some empirical relation for fish migration, particularly in two terms, that has been in wide usage for a long duration:  

• Catadromous Definition - It is the fish species that migrate from fresh water down into the sea to spawn, such as eels.

• Anadromous Definition - It is the fish that migrate from the sea up into freshwater to spawn, such as salmon, striped bass, and the sea lamprey.

• Diadromous, Amphidromous, Potamodromous, Oceanodromous - In a 1949 journal article, George S. Myers coined the inclusive term diadromous to refer to all fish that migrate between the sea and freshwater. Like the two well-known terms. Diadromous proved to be a useful word, but terms proposed by Myers for other types of diadromous fish did not catch on, which includes amphidromous (fish that migrate from freshwater to the seas, or vice versa, but not for the purpose of breeding), potamodromous (fish whose migrations occur wholly within freshwater), and oceanodromous (fish that live and migrate wholly in the sea). 

All these classifications are made on the basis of fish and their principle, so they are applicable to only aquatic organisms. 

Catadromous Fish

Catadromous fish species spend most of their lives in freshwater, but they migrate to the sea for the purpose of breeding. The best examples of catadromous fish are eels of the genus Anguilla, numbering 16 species. The best-known species among them is the North American eel (A. Rostrata) and the European eel (A. Anguilla).

European and North American eels breed in the warm, salty waters of the Atlantic, at depths of 400 to 700 feet (approximately 1,300 to 2,300 m), at an altitude of 26 ° N longitude 55 ° W called the Sargasso Sea.

Pelagic eggs that grow into leptocephali transparent, leaf-shaped forms with small heads - are carried by the Gulf Stream to the shallow water on the continental shelves. When it is about two and a half years old and about eight inches long (slightly more than three inches), a transformation takes place. The leptocephali are transformed into something called elvers, which are seated, colored, and in cylindrical form. They reached the shoreline as glass eels and began to swim upstream in the freshwater rivers. 

Their migration upstream is spectacular, as young fish gather in the millions, forming a dense weight several miles long. In freshwater the eels grow to full size, becoming yellow eels. They live like this for 10 to 15 years before turning into eels of silver, with enlarged eyes; they swam to the bottom of the sea, returned to the breeding grounds (Sargasso Sea), and then died. The migration of these eels is not fully understood, especially their return to the Sea of ​​Sargasso. European and North American eels may be similar.

Example of the Catadromous Species 

The catadromous migration is remarkable to the freshwater eels, some of the examples are the American eel and the European eel. They migrate larger distances from freshwater rivers to spawn in the sargasso sea, and whose subsequent larvae can drift in currents for months and even before coming back to the natural rivers and streams as glass eels (elvers). 

Anadromous Fish are saltwater creatures that travel to freshwater to reproduce. Their adaptations to the conditions of various habitats are precise, especially when it comes to water salinity. 

Salmon (Salmo, Oncorhynchus) spawn in lakes or higher streams where the water is cool and clean. Gravel beds are where eggs are placed. Atlantic salmon young stay in freshwater for two to three years, occasionally even six, while Pacific salmon migrate to the sea in their first year. Adult fish normally spend two or three winters in the sea, but sometimes only one. They then return to freshwater as grilse (adolescents) or adults to spawn, after undergoing changes in color and other exterior traits. After a single spawning, some Atlantic salmon perish in freshwater, while others return to the sea.

Salmon tagging has revealed that European species can migrate from Norway to Scotland and vice versa. Pacific salmon are most likely found in the Pacific Ocean and the Bering Sea, between 45 and 65 degrees north latitude, in surface waters ranging from 2 to 11 degrees Celsius (36 to 52 degrees Fahrenheit).

Young salmon traveling to the Pacific have been tagged in experiments in Canada and the United States, and it has been discovered that a large percentage of the fish return to the river where they hatched. The tagging of Atlantic salmon has revealed that a few survivors have returned to the same river two or even three times in the same year. 

Adults produced from experimentally transplanted eggs return to the stream in which they were hatched or grew, not the stream in which the eggs were laid.

Topographical characteristics are thought to play a significant role in recognizing the original habitat, in addition to other ways of orientation such as reference to astronomical objects. The sense of smell, often known as olfaction, plays the most crucial role. Migrating salmon are attracted to the waters of the stream where they will breed, according to experiments. Experiential imprinting occurs early in the development of a fish, allowing it to respond to waters that contain compounds with a specific odour or that have a specific temperature.

Example of the Anadromous Species 

Anadromous fishes have known species of about 100 approximately. Most of these species are a great asset to the commercial industry and hold a lot of value as well. 

Salmon, striped bass, steelhead trout, sturgeon, smelt, shad, and herring are among the many types of fish found in the area. Salmon have long been appreciated for their long, difficult migrations up rivers to their spawning sites, as well as the extraordinary homing skill that permits them to do so. Their ability to locate back to suitable mating grounds is particularly impressive, given that migration often follows a lengthy stay at sea, which can last up to five years. It's thought that chemical clues will lead them on their voyage.

Interesting Facts About Migrating Fish 

• Marine fish are also called diadromous, meaning they spend part of their life in freshwater and partly in freshwater. Diadromous fish or:

• Anadromous spend most of their adult life on the ocean but return to freshwater to reproduce.

• Catadromous, spends most of their adult lives in freshwater but returns to the sea to reproduce.

• Herring; herring is actually two different species of fish: alewives (Alosa pseudoharengus) and blueback herring (Alosa aestivalis).

• Measured by rapids, herring does not jump above them like salmon. They swim very fast and with short bursts.

• Alewives prefer to lay eggs overnight in slow-moving water and blueback herring prefer to breed on rocks during the day and in fast-moving waters.

• During the 1800s people ate most of the harvested alewives because they were well preserved in salt or when smoking. As the refrigerator expanded in the 20th century, demand for alewives for human consumption declined and other fish species were introduced.

• Atlantic sturgeon (Acipenser oxyrinchus) can grow up to 14 feet 14m in length, weigh 500 pounds 800kg, and live up to 60 feet 60m.

• Atlantic sturgeon is cartilaginous, meaning that its bones are mainly cartilage, not bone.

• The mouths of the Atlantic sturgeon occur. They can be excluded because their jaws are not really connected to any bone structure in their poles. This allows them to extract the spoils found at or below. Sturgeons also have large muscular belts that are strong enough to crush and separate digestive food. It helps because they have no teeth!

• Unlike Pacific salmon that breeds once and then dies, Atlantic salmon (Psalm salar) is iteroparous, meaning it does not die after giving birth and therefore can give birth more than once.

• Depending on the size of the female, the Atlantic salmon produces about 2,500 to 7,000 eggs. That is 600-800 eggs per kilogram of body weight! Why does it depend on female sizes? Usually, older females produce more eggs.

• In Norse mythology, Loki was the god of deception who tricked Hodr into killing the beloved Baldur. To escape the wrath of other Norse gods, Loki was transformed into a salmon. Thor interrupted Loki's escape by grabbing her by the tail. Thor's catch was so strong it formed a salmon's caudal peduncle, a small part of the fish's body that the tail attaches to the body.

• Archaeological evidence seems to confirm the myths that salmon has been revered for tens of thousands of years. The French Abri du Poisson, or "Fish Rock Shelter'', is adorned with a famous prehistoric 25,000-year-old Atlantic salmon painting. It is one of the oldest known fish representations, the only known fish statue of the Paleolithic period, and the shelter is a UNESCO World Heritage site.

Fun Facts

Diadromous fish are important contributors to nutrient transport in freshwater and inland habitats. They migrate out of streams when they're young and grow enormously on the nutrients in the ocean. Because many species die soon after returning to their native stream, their bodies contribute vital nutrients to these freshwater habitats. 

The largest migratory fish in the US ever recorded being 126 lbs was chinook salmon. Chinook salmon do not even weigh anything more than 30 lbs. 

Salmon can jump as high as 6.5 feet in the air, which aids them in their upstream swim to spawning sites. The depth of the landing pool after such a leap, on the other hand, can be just as crucial for fish migration as the height of potential barriers.

Rainbow trout and steelhead trout are the same species of fish, with rainbow trout being the freshwater form and steelhead trout being the migratory version. Unlike much migratory fish, steelhead does not necessarily perish after spawning and might make multiple voyages back and forth between the ocean and their natal stream over the course of their lives.

Conclusion

The chapter Catadromous fish migration is available on the Vedantu website. Students can get important questions and answers, study materials, revision notes, and mock test papers from the website in PDF format that are designed by experienced and expert teachers.