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72-444: More than 150 Tetra is the common name of many small freshwater characiform fishes. Tetras come from Africa , Central America , and South America , belonging to the biological family Characidae and to its former subfamilies Alestidae (the "African tetras") and Lebiasinidae . The Characidae are distinguished from other fish by the presence of a small adipose fin between the dorsal and caudal fins . Many of these, such as

144-497: A family of ray-finned fish that contains the freshwater eels . All the extant species and six subspecies in this family are in the genus Anguilla , and 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 . Eels are an important food fish and some species are now farm-raised , but not bred in captivity. Many populations in

216-446: A homocercal caudal fin (a twin-lobed, or forked, tail fin whose upper and lower lobes are of equal size) and a tall dorsal fin characterized by a short connection to the fish's body. Additionally, tetras possess a long anal fin stretching from a position just posterior of the dorsal fin and ending on the ventral caudal peduncle, and a small, fleshy adipose fin located dorsally between the dorsal and caudal fins. This adipose fin represents

288-494: A lack of knowledge of the biology of these species, especially in their social and spawning behavior, as well as a lack of long-term data sets. Anguillid eels are important food fish. Eel aquaculture is a fast-growing industry. Important food eel species include longfin eel, Australian long-finned eel, short-finned eel, and Japanese eel. Most eel production historically has been in Japan , Korea , and Taiwan , but in recent years,

360-513: A piece perfectly sized for them. Population density sex determination is a feature where the Anguillidae regulate their population's gender depending on the abundance of eggs present. High egg concentrations will result in more male than female ratios as well as vice versa. It does not mean that the eggs will all become one sex but rather have a higher ratio in one of the two sexes present.   Mucous cells within epidermis are found in both

432-440: A result of synchronicity in response to environmental conditions. These eels are known as generalists and opportunistic feeders; most will consume whatever acceptable prey they happen upon, including things like crustaceans, fishes, and other aquatic fauna. Aside from their reduced pectoral fins, eels lack of paired appendages: use axial-based lateral undulation as means of locomotion, similar to snakes. High maneuverability of trunk

504-537: A scapula is important in muscle attachment and allows for the upper head to move in various directions as well as increase strength of body undulation, thus increasing swimming capabilities. The presence of a scapula allows for stronger movements of pectoral fins which aid in movement across terrestrial obstacles. Cutaneous respiration accounts for approximately fifteen percent of their oxygen intake but when they are out of water, they are capable of receiving approximately fifty percent of their oxygen through gas exchange via

576-743: A single migration loop. Migration loops may be flexible in some species, and this variability is still being investigated. However, some eels in this family have altered their migration loop to become completely marine, not returning to fresh waters to develop. Ocean-resident eels are the exception of this family, and this behavior may be more common in areas in which the freshwater habitat is of lower quality or productivity. Anguillid eels are semelparous , meaning they only live to reproduce once, as they die after reproduction. However, these eels do not necessarily reproduce every year-they will sometimes wait until conditions are right in order to migrate and breed. The European eel can spawn starting at 7 years old, and

648-479: A single serving typically significantly increasing the blood PFOS level. About four in ten North American freshwater fish are endangered, according to a pan-North American study, the main cause being human pollution. The number of fish species and subspecies to become endangered has risen from 40 to 61, since 1989. For example, the Bigmouth Buffalo is now the oldest age-validated freshwater fish in

720-427: A stronger cranium which aids in their variable burrowing tendencies with mud as well as maneuvering through terrestrial obstacles when hiding under rocks and logs that they encounter at the waters bottom where they spend most of their time during the day. Ventral lateral gill slits make up eighty-five percent of gas exchange and are highly efficient in converting between salt and freshwater. This feature really separates

792-414: A water temperature of 50 to 60 °F (10–16 °C). In North America, air temperatures that result in sufficiently cold water temperatures are found in the northern United States, Canada, and in the southern United States at high elevation . Common coldwater fish include brook trout , rainbow trout , and brown trout . Coolwater fish species prefer water temperature between the coldwater and

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864-483: Is Anguilla ignota and was found in Messel, Germany. The Messel fossil deposit is dated to be 43.8 million years old during the mid-Eocene epoch. During this time period, Messel was undergoing intense volcanic activity which resulted in the formation of freshwater maar lakes. A. ignota was found in the geological remains of one of these lakes, which makes it the oldest eel to inhabit a freshwater environment. Arguably,

936-403: Is a big part in the lives of Anguillidae and many changes happen in preparation for migration amongst the adults going from the yellow eel stage to the silver eel stage. The gas bladder adapts for higher pressures which it'll be exposed to in the ocean where it will dive much deeper in search of food and avoiding strong currents. Fat reserves increase in preparation for less abundant food sources in

1008-498: Is a general consensus that Anguillidae are firmly nested within Anguilliformes. Traditionally, molecular studies have placed Anguillidae in the subclass "Anguilloidei" with two other families: Nemichthyidae (snipe eels) and Serrivomeridae (sawtooth eels). Until 2013, this subclass has been lumped together into a cohesive clade. However, recent molecular studies have suggested that Anguillidae are actually more closely related to

1080-566: Is a vital part of aquatic ecosystem stability, so changes to stream and river water temperature can have large impacts on biotic communities. Many aquatic larvae use thermal cues to regulate their life cycles, mostly notably here, insects. Insects are a large part of most fish diets, so this can pose a great dietary problem. Temperature can cause changes in fish behavior and distribution habits as well by increasing their metabolic rates and thus their drive to spawn and feed. Linear systems are more easily fragmented and connectivity in aquatic ecosystems

1152-439: Is adaptation for hunting in structurally-complex habitats such as reefs. Some species are known to burrow into the sea bed/sediment, including species that utilize head-first or tail-first burrowing techniques. This is related to both foraging and anti-predatory behavior. Freshwater eels have several natural predators such as large fish and piscivorous birds.  Much is unknown about Anguillid eel behavior and its origins, due to

1224-452: Is an increasing trend in freshwater fish for local taxonomic, functional, and phylogenetic richness in more than half of the world's rivers. This increase in local diversity is primarily explained by anthropogenic species introductions that compensate for or even exceed extinctions in most rivers. A study and an interactive map by EWG using its results show freshwater fish in the U.S. ubiquitously contain high levels of harmful PFAS , with

1296-575: Is defined as a species that does not naturally occur in a certain area or ecosystem. This includes eggs and other biological material associated with the species. Non-native species are considered invasive if they cause ecological or economic injury. The introduction of exotic fish species into ecosystems is a threat to many endemic populations. The native species struggle to survive alongside exotic species which decimate prey populations or outcompete indigenous fishes. High densities of exotic fish are negatively correlated with native species richness. Because

1368-597: Is invasive worldwide, and there are multiple efforts to remove them from their non-native ecosystems. Both species are among the " 100 of the World’s Worst Invasive Alien Species ," as determined by the IUCN Invasive Species Specialist Group based on their effect on anthropogenic activities, environmental biodiversity and their ability to act as a case study for important ecological issues. Hybridization involves

1440-472: Is not as prominent in length. Their body movement depends highly on undulation originating near the anterior axial end. Due to the fins being fused we see a highly skilled swimmer amongst the Anguillidae which aids in migration and hunting/predation. It was mistakenly reported that Anguillidae lack a scapular bone but after further research and more advanced staining techniques they have a scapula and coracoid which make up their pectoral girdle . The presence of

1512-456: Is primarily due to the rapid speciation that the scattered habitats make possible. When dealing with ponds and lakes, one might use the same basic models of speciation as when studying island biogeography . Freshwater fish differ physiologically from saltwater fish in several respects. Their gills must be able to diffuse dissolved gases while keeping the electrolytes in the body fluids inside. Their scales reduce water diffusion through

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1584-442: Is vital. Freshwater fishes are particularly vulnerable to habitat destruction because they reside in small bodies of water which are often very close to human activity and thus easily polluted by trash, chemicals, waste, and other agents which are harmful to freshwater habitats. Land use changes cause major shifts in aquatic ecosystems. Deforestation can change the structure and sedimentary composition of streams, which impacts

1656-912: The European eel ( A. anguilla ), the American eel ( A. rostrata ), the Japanese eel ( A. japonica ), the New Zealand longfin eel ( A. dieffenbachii ), and the Indonesian longfinned eel ( A. borneensis ). Threats to these species include: habitat loss/modification, migration barriers, pollution, parasitism, exploitation, and consumption, as eels are a popular food source especially in Asia and Europe. Fluctuating oceanic conditions associated with climate change also make these species vulnerable, with reduced water quality leading to biodiversity loss among

1728-429: The fishkeeping hobby , many unrelated fish are commonly known as tetras, including species from different families. Even vastly different fish may be called tetras. For example, payara ( Hydrolycus scomberoides ) is occasionally known as the " sabretooth tetra " or "vampire tetra". Tetras generally have compressed (sometimes deep), fusiform bodies and are typically identifiable by their fins. They ordinarily possess

1800-413: The neon tetra ( Paracheirodon innesi ), are brightly colored and easy to keep in captivity. Consequently, they are extremely popular for home aquaria . Tetra is no longer a taxonomic , phylogenetic term. It is short for Tetragonopterus , a genus name formerly applied to many of these fish, which is Greek for "square-finned" (literally, four-sided-wing). Because of the popularity of tetras in

1872-477: The sea lamprey have different tolerances in salinity in different stages of their lives. Among fishers in the United States, freshwater fish species are usually classified by the water temperature in which they survive. The water temperature affects the amount of oxygen available as cold water contains more oxygen than warm water. Coldwater fish species survive in the coldest temperatures, preferring

1944-431: The skin : freshwater fish that have suffered too much scale loss will die. They also have well developed kidneys to reclaim salts from body fluids before excretion . Many species of fish do reproduce in freshwater, but spend most of their adult lives in the sea. These are known as anadromous fish, and include, for instance, salmon , trout , sea lamprey and three-spined stickleback . Some other kinds of fish are, on

2016-780: The 1960s. Although about 90% of freshwater eels consumed in the US are farm-raised , they are not bred in captivity . Instead, young eels are collected from the wild and then raised in various enclosures. In addition to wild eel populations being reduced by this process, eels are often farmed in open-net pens, which allow parasites , waste products, and diseases to flow directly back into wild eel habitat, further threatening wild populations. Freshwater eels are carnivores so are fed other wild-caught fish, adding another element of unsustainability to current eel-farming practices. Freshwater eels are aquatic and live in various habitats, including freshwater, estuaries, and saltwater/marine habitats, and occupy

2088-454: The Anguillidae, are capable of responding to the geomagnetic field and will alter their direction of interest accordingly. They depend on the intensity and inclination of the magnetic field to migrate. Within this experiment they also looked at how the glass eel may rely on the circatidal rhythm in the ocean to work its way back to the coast and into the freshwater systems, but it is not yet fully understood. Paired frontal bones of skull make for

2160-428: The Anguillidae, freshwater eels, from other eels who have internal gill chambers. Many species have variegated skin which means they will vary in color depending on their environment so that they can maintain the highest grade of camouflage. The dorsal, anal and caudal fins are fused and pelvic fins are lacking. Dorsal fin begins mid body creating a long continuous fin where in other species it begins more posterior and

2232-494: The Nile perch into Lake Victoria, possibly to improve sport fishing and boost the fishery. In the 1980s, the Nile perch population saw a large increase which coincided with a great increase in the value of the fishery. This surge in Nile perch numbers restructured the lake's ecology. The endemic cichlid population, known to have around 500 species, was cut almost in half. By the 1990s, only three species of sport fish were left to support

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2304-469: The Saccopharyngiforms (Gulpers and relatives) than they are to the other Anguilloid families. This leads to two possibilities: Either Anguilloidei is a paraphyletic group, or it was originally delineated inaccurately, and Anguillidae should not be included in this subclass. However, more studies need to be conducted to confirm the placement of freshwater eels within Anguilliformes, and determine

2376-491: The Santonian-Campanian Calcari di Melissano, which is a fossil bed located near the town of Nardò. Strontium-isotope stratigraphy concluded the age of N. robinsi to be 83 million years old. The fossil was discovered incomplete and lacked the skull and part of the anterior skeleton. Despite the morphological uncertainty, cranial and branchial features confirmed it was an eel. At first, it was classified

2448-551: The composition of the Anguilloidei subclass. Anguillid eels have a global distribution, and inhabit the waters of more than 150 countries. They are mainly found in tropical and temperate waters, except in the Eastern Pacific and South Atlantic. Conservation is difficult for this taxon because not much is known about their life history and behaviors. However, many Anguillid eels are of conservation concern, including

2520-516: The contrary, born in salt water, but live most of or parts of their adult lives in fresh water; for instance the eels . These are known as catadromous fish . Species migrating between marine and fresh waters need adaptations for both environments; when in salt water they need to keep the bodily salt concentration on a level lower than the surroundings, and vice versa. Many species solve this problem by associating different habitats with different stages of life. Both eels, anadromous salmoniform fish and

2592-711: The cycle anew. The discovery of the spawning area of the American and European eels in the Sargasso Sea is one of the more famous anecdotes in the history of ichthyology . The spawning areas of some other anguillid eels, such as the Japanese eel, and the giant mottled eel, were also discovered recently in the western North Pacific Ocean. Eels in the family Anguillidae are known to be primarily solitary in nature; they are not known to communicate socially or actively school, however large masses of elvers can be found as

2664-474: The degradation of the Yangtze, alongside that of the wild Yangtze sturgeon . Intentional anthropogenic reconstruction and rerouting of waterways impacts stream flow, water temperature, and more, impacting normal habitat functionality. Dams not only interrupt linear water flow and cause major geological channel shifts, but also limit the amount of water available to fishes in lakes, streams and rivers and have

2736-506: The difficulty in observation, particularly in the context of reproduction, social constructs, and migration. Anguillidae unlike its other relatives have a fully developed lateral line along their trunk. Lateral lines provide the ability for Anguillidae to sense their surrounding environment through water displacement which aids in predation and hunting especially because they are predominantly nocturnal generalists.   Olfactory senses in this family are heightened for various reasons. Within

2808-551: The earliest member of the eel family, Ophichthidae (snake eels). However, upon further inspection, the fossil only displayed one synapomorphy of snake eels, and possessed morphological features more congruent with an ancestral anguilliform. Therefore, many phylogenetic studies use this fossil as a calibration point to date crown anguilliforms. Therefore, if the oldest eel is 83 million years old, it can be concluded that anguillidae could not have originated any earlier than that. The earliest known, unequivocal fossil of an anguillid eel

2880-427: The eels become pigmented and develop through the elver and yellow eel stages. The yellow and silver eel stages are named aptly for the coloration of the underbelly of the eel during these developmental stages. Elvers travel upstream in freshwater rivers, where they grow to adulthood. Finally, anguillids transition through the silver eel stage into adulthood and migrate to the oceanic breeding grounds to reproduce and begin

2952-570: The epidermis. Additionally, freshwater eels possess small, granular teeth arranged in bands on the jaws and vomer. Anguillidae do exhibit size-dependent sexual dimorphism. Male anguillids invest more energy into mating with as many females as he can, than they do into growth. Therefore, female anguillids are usually larger, ranging from 1.5–3 feet (0.46–0.91 m), while male anguillids rarely get larger than 1.5 feet (0.46 m) long. Adult anguillidae can vary in color, but normally are brown, olive or olive-yellow, and can be mottled. Coloration matches

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3024-580: The exotic species is suddenly introduced to a community, it does not have any established predators or prey. The exotic species then have a survival advantage over endemic organisms. One such example is the destruction of the endemic cichlid population in Lake Victoria via the introduction of the predatory Nile perch ( Lates niloticus ). Although the exact time is unknown, in the 1950s the Ugandan Game and Fisheries Department covertly introduced

3096-499: The extinction of the yellowfin cutthroat trout ( Oncorhynchus clarkii macdonaldi ) found only in the Twin Lakes of Colorado, USA. The yellowfin cutthroat trout was discovered in 1889 and was recognized as a subspecies of the cutthroat trout ( Oncorhynchus clarkii ). The rainbow trout was introduced to Colorado in the 1880s. By 1903, the yellowfin cutthroat trout stopped being reported. It is now presumed extinct. The rainbow trout

3168-420: The family Centrarchidae . In 2021, a group of conservation organizations estimated that one-third of the world's freshwater fish species were at risk of extinction. A global assessment of freshwater fishes estimates an average decline of 83% in populations between 1970 and 2014. The protection of 30% of Earth's surfaces by 2030 may encompass freshwater habitat and help protect these threatened species. There

3240-424: The floor of rivers and lakes which prevents the eels from being seen by predators while in clear or shallow water. Freshwater eels go through physical changes in their bodies when going to and from the ocean for different stages of life. There are two important fossils used to date the origin of freshwater eels. The first is the fossil Nardoechelys robinsi which represents the ancestor to all extant eels, and marks

3312-491: The fourth unpaired fin on the fish (the four unpaired fins are the caudal fin, dorsal fin, anal fin, and adipose fin), lending to the name tetra, which is Greek for four. While this adipose fin is generally considered the distinguishing feature, some tetras (such as the emperor tetras, Nematobrycon palmeri ) lack this appendage. Ichthyologists debate the function of the adipose fin, doubting its role in swimming due to its small size and lack of stiffening rays or spines. Although

3384-463: The greatest production has been in China. Seafood Watch , one of the better-known sustainable seafood advisory lists , recommends consumers avoid eating anguillid eels due to significant pressures on worldwide populations. Several species used as unagi have seen their population sizes greatly reduced in the past half century. Catches of the European eel , for example, have declined about 80% since

3456-460: The habitat functionality for many fish species and can reduce species richness, evenness, and diversity. Agriculture, mining, and basic infrastructural building can degrade freshwater habitats. Fertilizer runoffs can create excess nitrogen and phosphorus which feed massive algae blooms that block sunlight, limit water oxygenation, and make the habitat functionally unsustainable for aquatic species. Chemicals from mining and factories make their way into

3528-599: The largest threats. In the Northern hemisphere, anguillid eels have had large declines in populations due to a number of reasons including overexploitation and migration inhibition via migration barriers. According to the IUCN Anguillid Eel Specialist Group, or the AESG, the need for conservation of this family is clear given recent declines. However, conservation efforts are being inhibited by

3600-427: The list below is sorted by common name, in a number of cases, the common name is applied to different species. Since the aquarium trade may use a different name for the same species, advanced aquarists tend to use scientific names for the less-common tetras. The list below is incomplete. Tetra species: A–D E–Q R–Z Freshwater fish 41.24% of all known species of fish are found in fresh water. This

3672-612: The long warmwater species, around 60 to 80 °F (16–27 °C). They are found throughout North America except for the southern portions of the United States. Common coolwater species include muskellunge , northern pike , walleye , and yellow perch . Warmwater fish species can survive in a wide range of conditions, preferring a water temperature around 80 °F (27 °C). Warmwater fish can survive cold winter temperatures in northern climates, but thrive in warmer water. Common warmwater fish include catfish , largemouth bass , bluegill , crappies , and many other species from

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3744-409: The lower-boundary of the age of anguillidae. The second is Anguilla ignota , which is the fossil that represents the ancestor to all extant freshwater eels and marks the upper boundary of the age of anguillidae. Using these two fossil calibration points, freshwater eels are said to originate between 83 million years ago and 43.8 million years ago. N. robinsi was found by Italian scientists in 2002 in

3816-460: The mating of two genetically different species ( interspecific hybridization ). It is dangerous for native species to hybridize because hybrid phenotypes may have better fitness and outcompete the two parent species and/or other fishes in the ecosystem. This could irreversibly compromise the genetic identity of one or both of the parent species and even drive them to extinction if their range is limited. The rainbow trout discussed above hybridized with

3888-427: The most defining feature of Anguillidae is the fact that they inhabit freshwater, being the only family of eels to do so. Therefore, the hypothesis stating that A. ignota is the ancestor to all freshwater eels is strongly supported. This fossil is commonly used as a calibration fossil to pinpoint the lower boundary of the age of freshwater eels. The exact placement of freshwater eels is still being debated, but there

3960-440: The most important specialized senses in this family. Unlike the other relatives the Anguillidae are catadromous meaning they must migrate for an extended period and depending on what life stage they are in they may be in the open ocean. The Anguillidae were placed in “magnetic displacement” experiment where the geomagnetic north could be altered, and their actions could be monitored. The results showed that at different stages of life,

4032-585: The mud and wait for rain while undergoing torpor. Since rain is not predictable torpor allows for the organism to lower its metabolic rate as well as its body temperature increasing its survivability.   Anguillidae are great swimmers due to their axial muscle attachment and W-shaped myomeres giving them the capability of swimming backwards just as well as they can swim forward. Not many other fish can do so. Since their mouths are not very large, they use their swimming capabilities to aid in feeding where they will bite onto their food and twist/spin rapidly tearing off

4104-402: The nasal sac are olfactory cells which have the capability of detecting extremely diluted chemicals as low as three to four molecules. This is extremely helpful in their nocturnal endeavors as well as for migratory purposes. They use terrestrial odors as cues in migration as well as low salinity and colder temperatures to direct themselves.   Geomagnetic sensing has been identified as one of

4176-597: The native greenback cutthroat trout ( Oncorhynchus clarkii stomias ), causing their local extinction in the Twin Lakes area of Colorado as their hybrid " cutbows " became more prevalent. The rainbow trout has been reported to hybridize with at least two other salmonid species. Additionally, the cichlids in Lake Victoria evolved over 700 unique species in only 150,000 years and are theorized to have done so via ancient hybridization events which led to speciation. Anguillidae See text The Anguillidae are

4248-429: The non-sexually mature and sexually mature adult stages. The mucous cells are made of glycoproteins which are found in higher concentrations on dorsal and ventral sides of body. It is believed that the family Anguillidae has higher concentrations of slime than other families. This aids in predation as well as helping keep themselves moist outside of water increasing efficiency of cutaneous respiration.   Metamorphosis

4320-498: The number of fish species in the ecological community. Additionally, dams can cause the isolation of fish populations, and the lack of connectivity creates possible problems for inbreeding and low genetic diversity. The loss of connectivity impacts the structure of community assemblies and increases the fragmentation of habitats, which can compound existing problems for vulnerable species. Temperature alterations are another unintended consequence of dam and land use projects. Temperature

4392-400: The ocean to breed. Leptocephali (larval) migration can range from months to up to almost a year. Temperate eels migrate on average for approximately 6–10 months, while tropical eels undergo shorter migrations between approximately 3–5 months on average. The European eel ( A. anguillidae ) has one of the longest migrations of all freshwater eels, migrating up to 6000 km (over 3700 miles) in

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4464-703: The ocean, and once hatched, enter a larval stage called leptocephali . The young eel larvae live only in the ocean and consume small particles called marine snow . Anguillid eels lay adhesive demersal eggs (eggs that are free-floating or attached to substrate), and most species have no parental care. Japanese eels ( A. japonica ) can lay between 2 million and 10 million eggs. These planktonic (free floating) eggs and translucent, leaf-like larvae are dispersed via ocean currents and migrate sometimes thousands of miles. They grow larger in size, and in their next growth stage, they are called glass eels. At this stage, they enter estuaries -upon returning to freshwater growing habitat,

4536-419: The ocean. Females will experience a higher increase than males for the reason of egg production. The eyes also change increasing in size by two times and retinal pigments which are sensitive to red light in shallow waters change to pigments that are sensitive to blue light which is better adapted for the deep ocean that the silver eel will be experiencing.   One experiment talked about the driving force that

4608-410: The oldest of this species that has been found in the wild was 85 years of age. These conditions may include fat content, water quality or temperature, prey availability, river height and water flow rate, etc. This variability allows some eels to live even 50–70 years, however the lifespan of freshwater eels is not well documented. Very little is known about the mechanics of fertilization and spawning, and

4680-422: The once multispecies fishery, two of which were invasive. More recent research has suggested that remaining cichlids are recovering due to the recent surge in Nile perch commercial fishing, and the cichlids that are left have the greatest phenotypic plasticity and are able to react to environmental changes quickly. The introduction of the rainbow trout ( Oncorhynchus mykiss ) in the late 19th century resulted in

4752-399: The outer integument. This is an important feature since Anguillidae at many times need to move between bodies of water to maintain an aquatic environment. It is also known that they will burrow down into mud so having the capability to exchange gas outside of water is highly beneficial to this family.   It is known that when bodies of water start to dry up the Anguillidae burrow down into

4824-472: The potential to change the trophic structure because of these alterations of the habitat and the limitations to movement and connectivity. Unnatural water flow below dams causes immense habitat degradation, reducing viable options for aquatic organisms. Upstream migration is hindered by the dam structure and can cause population declines as fishes don't have access to normal feeding and/or spawning grounds. Dams tend to affect upstream species richness, that is,

4896-448: The roles of both predator and prey, and evidence has been found of nematode parasitism in some species. Some eel species have been observed consuming the eggs of predatory fish such as trout, aiding in population control in these systems. Juvenile eels occupy small spaces in between rocks, in crevices or mud. Freshwater eels are widespread and are catadromous, meaning they spend most of their life in freshwater (rivers mainly) and migrate to

4968-653: The soil and go into streams via runoff. More runoff makes its way into streams since paved roads, cement, and other basic infrastructure do not absorb materials, and all the harmful pollutants go directly into rivers and streams. Fish are very sensitive to changes in water pH, salinity, hardness, and temperature which can all be affected by runoff pollutants and indirect changes from land use. Freshwater fish face extinction due to habitat loss, overfishing, and " forever chemicals ." Conservation efforts, sustainable practices, and awareness are crucial in maintaining fish populations and species diversity. An exotic (or non-native) species

5040-678: The time it takes these eels to hatch from their eggs is variable. Tsukamoto and associates found evidence of Japanese eels ( A. japonica ) may synchronize their breeding cycles during the spawning season with the new moon. Members of this family spend their lives in freshwater rivers , lakes , or estuaries , and return to the ocean to spawn. All eels pass through several stages of development through their life cycle. Anguillid eels undergo morphological changes during these developmental stages that are associated with environmental conditions and aid in preparing them for further growth and finally reproduction. Anguillid eels begin their life as an egg in

5112-625: The wild are now threatened, and Seafood Watch recommend consumers avoid eating anguillid eels. Adult freshwater eels are elongated with tubelike, snake-shaped bodies. They have large, pointed heads and their dorsal fins are usually continuous with their caudal and anal fins, to form a fringe lining the posterior end of their bodies. They have relatively well developed eyes and pectoral fins compared to saltwater eels that they use to navigate and maneuver through river bottoms and shallow water. Unlike most eels, freshwater eels have not lost their scales, and instead have soft, thin, scales that are embedded in

5184-552: The world, and its status urgently needs reevaluation in parts of its endemic range. About 2 ⁄ 3 of the total freshwater fisheries in China are in the Yangtze Basin. Many Yangtze fish species have declined drastically and 65 were recognized as threatened in the 2009 Chinese red list . The Chinese paddlefish , once common to the Yangtze River, is one of a number of extinctions to have taken place due to

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