Fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

go through various life stages between

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Pro ...

and adulthood. The life of a fish start as

spawn Spawn or spawning may refer to: * Spawn (biology), the eggs and sperm of aquatic animals Arts, entertainment, and media * Spawn (character), a fictional character in the comic series of the same name and in the associated franchise ** '' Spawn: A ...

ed eggs which hatch into immotile larvae. These larval

hatchling In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird. A group of mammals called monotremes lay eggs, and their young are hatchlings as well. Fish Fish hatchlings generally do not receive parental care, similar to ...

s are not yet capable of feeding themselves and carry a

yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...

which provides stored nutrition. Before the yolk sac completely disappears, the young fish must mature enough to be able to

forage Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also use ...

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 finger A finger is a limb of the body and a type of digit, an organ of manipulation and sensation found in the hands of most of the Tetrapods, so also with humans and other primates. Most land vertebrates have five fingers (Pentadactyly). Chambers ...

s. The juvenile stage lasts until the fish is fully grown,

sexually mature Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definiti ...

and interacting with other adult fish.

Growth stages

Ichthyoplankton Ichthyoplankton (from Greek: ἰχθύς, , "fish"; and πλαγκτός, , "drifter") are the eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epi ...

''(planktonic or drifting fish)'' are the eggs and

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

e of fish. They are usually found in the sunlit zone of the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

, less than 200 metres deep, sometimes called the epipelagic or

photic zone The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological pro ...

. Ichthyoplankton are

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

ic, meaning they cannot swim effectively under their own power, but must drift with ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juveniles. Fish larvae are part of the

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.What are Ichthyoplankton?
Southwest Fisheries Science Center, NOAA. Modified 3 September 2007. Retrieved 22 July 2011.Moser HG and Watson W (2006
"Ichthyoplankton"
Pages 269–319. In: Allen LG, Pondella DJ and Horn MH, ''Ecology of marine fishes: California and adjacent waters'' University of California Press. . According to Kendall et al. 1984Kendall Jr AW, Ahlstrom EH and Moser HG (1984
"Early life history stages of fishes and their characters"
''American Society of Ichthyologists and Herpetologists'', Special publication 1: 11–22. there are three main developmental stages of fish: * Egg stage: From

ing to hatching. This stage is named so, instead of being called an

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

nic stage, because there are aspects, such as those to do with the egg envelope, that are not just embryonic aspects. * Larval stage: From the eggs hatching till to when

fin ray Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

s are present and the growth of protective scales has started (squamation). A key event is when the

notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consi ...

associated with the tail fin on the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

side of the spinal cord develops and becomes flexible. A transitional stage known as the ''sac larval'' stage, lasts from hatching to the complete resorption of the

. * Juvenile stage: Starts when the morphological transformation or

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

from larva to juvenile is complete, that is, when the larva develops the features of a functional fish. These features are that all the fin rays are present and that scale growth is under way. The stage completes when the juvenile becomes adult, that is, when it becomes

or starts interacting with other adults. This article is about the larval and juvenile stage. * Hatchling – refers to a recently hatched fish larva that is still too immature to achieve

motility Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...

, and therefore not yet capable of active feeding. A hatchling still possesses a

upon which it depends for nutrition, and are thus also known as a sac fry. * Fry – refers to a more developed hatchling whose yolk sac has almost disappeared, and its

swim bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth wit ...

is functional to the point where the fish can move around and perform limited

foraging Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavi ...

to nourish itself.Guo Z, Xie Y, Zhang X, Wang Y, Zhang D and Sugiyama S (2008) tp://ftp.fao.org/docrep/fao/010//i0111e/i0111e00.pdf ''Review of fishery information and data collection systems in China''Page 38. FAO Fisheries and Aquaculture, Circular 1029. FAO, Rome. . At this stage, the fish usually filter-feeds on

s as it is still too small and slow to venture away from covers without being consumed by

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...

s. * Fingerling – refers to a fish that has reached the stage where the fins can be extended and protective scales have covered the body. At this stage, the fish is typically about the size of a

, hence the name. Once reaching this stage, the fish can be considered a juvenile, and is usually active enough to move around a large area. The feeding diet also changes from planktons to

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...

s and

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

, occasionally other fish. The fish also starts to morphologically resemble

adult An adult is a human or other animal that has reached full growth. In human context, the term ''adult'' has meanings associated with social and legal concepts. In contrast to a " minor", a legal adult is a person who has attained the age of maj ...

fish gradually (though still smaller), although it is not yet achieved sexual maturity.

Juvenile salmon

Fry and fingerling are generic terms that can be applied to the juveniles of most fish species, but some groups of fishes have juvenile development stages particular to the group. This section details the stages and the particular names used for juvenile salmon. * ''Sac fry'' or ''alevin'' – The life cycle of salmon begins and usually also ends in the

backwater Backwater or Backwaters may refer to: Music * ''Backwaters'' (album), a 1982 album by American guitarist Tony Rice * Backwater (band), a jazz fusion band from Mobile, Alabama, or this band's 1976 debut album * "Backwater", a song by Brian Eno fr ...

s of streams and rivers. These are their

spawning 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 aquat ...

grounds, where salmon eggs are deposited for among the

gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifi ...

s of

stream bed A stream bed or streambed is the bottom of a stream or river ( bathymetry) or the physical confine of the normal water flow ( channel). The lateral confines or channel margins are known as the stream banks or river banks, during all but fl ...

s. The salmon spawning grounds are also the salmon nurseries, providing a more protected environment than the ocean usually offers. After 2 to 6 months the eggs hatch into tiny salmon

e called ''sac fry'' or ''alevin''. These

s have a

containing the remainder of the

yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example ...

and they stay hidden in the gravels for a few more days, as they are still largely immobile and rely on the remaining nutrients stored in the sac for survival. * ''Fry'' – When the larvae develop further, their yolk sac gets deplete. Once the sac is almost completely gone the larvae must begin

food by themselves, so they leave the protection of the gravel bed and start using their now-stronger

tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammal ...

s to swim around feeding on

s. At this point these mobile alevins become ''fries''. * ''Parr'' – Roughly when a fry have grown to the size of a

, it develops protective scales and sufficiently strong fins and are thus colloquially known as a ''fingerling''. Fingerlings will start altering to a more

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

diet and quickly gain body mass, and at the end of the summer they develop into juvenile salmon called ''parr''. Parr feed on small

s and are camouflaged with a pattern of spots and vertical bars. They remain in this stage for up to three years.Bley 1988Lindberg 2011 Some older male parr are even already able to fertilize adult females' eggs in the spawning season, without having passed through the subsequent stages of development, and compete to do so with much larger

anadromous 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 thousa ...

adult males returning from the sea. * ''Smolt'' – As they approach the time when they are ready to migrate out to the sea, the parr lose their camouflage bars and undergo a process of physiological changes that allows them to survive a shift from freshwater to saltwater environments. At this point these young salmon are called ''smolt''. Smolt spend time in the

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estua ...

waters of the

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environme ...

while their body chemistry adjusts (

osmoregulation Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration o ...

) to the higher salt levels they will encounter in the ocean.''Atlantic Salmon Trust'' 2011 Smolt also grow the silvery scales with

countershading Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish ...

, which visually confuse ocean predators. * ''Post-smolt'' – When they have matured sufficiently in late spring and are about 15 to 20 centimetres long, the smolt swim out of the rivers and into the sea. There they spend their first year as ''post-smolt''. Post-smolt form

schools A school is an educational institution designed to provide learning spaces and learning environments for the teaching of students under the direction of teachers. Most countries have systems of formal education, which is sometimes compulsor ...

with other post-smolt and set off to find deep-sea feeding grounds. They then spend up to four more years as adult ocean salmon while their full swimming and reproductive capacity develops. File:Salmo salar eggs.jpg, Salmon eggs. The growing larvae can be seen through the transparent egg envelope. The black spots are the eyes. File:Salmonlarvakils 2.jpg, Salmon egg hatching into a ''sac fry''. In a few days, the sac fry will absorb the yolk sac and become a salmon fry File:Atlantic salmon redd.jpg, Sac fry remain in the gravel habitat of their redd (nest) while their yolk sac, or "lunch box" is depleted ''(click to enlarge)'' File:SalmonoidsBergeau.jpg, The juvenile salmon, ''parr'', grow up in the relatively protected natal river File:Coho.jpg, The parr lose their camouflage bars and become ''smolt'' as they become ready for the transition to the ocean File:Salmo salar GLERL 1.jpg, Salmon enter the ocean as ''post-smolt'' and mature into adult salmon. They gain most of their weight in the ocean

Protection from predators

Juvenile fish need protection from predators. Juvenile species, as with small species in general, can achieve some safety in numbers by schooling together.Bone Q and Moore RH (2008
''Biology of Fishes''
pp. 418–422, Taylor & Francis Group. Juvenile coastal fish are drawn to turbid shallow waters and to

mangrove A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...

structures, where they have better protection from predators. As the fish grow, their foraging ability increases and their vulnerability to predators decreases, and they tend to shift from mangroves to

mudflat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal f ...

s. In the open sea juvenile species often aggregate around floating objects such as jellyfish and '' Sargassum '' seaweed. This can significantly increase their survival rates.

As human food

Juvenile fish are marketed as food. * ''

Whitebait Whitebait is a collective term for the immature fry of fish, typically between long. Such young fish often travel together in schools along coasts, and move into estuaries and sometimes up rivers where they can be easily caught using fine-m ...

'' is a marketing term for the fry of fish, typically between 25 and 50 millimetres long. Such juvenile fish often travel together in

along the coast, and move into

and sometimes up rivers where they can be easily caught with fine meshed

fishing net A fishing net is a Net (device), net used for fishing. Nets are devices made from fibers woven in a grid-like structure. Some fishing nets are also called fish traps, for example #Fyke nets, fyke nets. Fishing nets are usually meshes formed by ...

s. ''Whitebaiting'' is the activity of catching whitebait. Whitebait are tender and edible, and can be regarded as a delicacy. The entire fish is eaten including head, fins and gut. Some species make better eating than others, and the particular species that are marketed as "whitebait" varies in different parts of the world. As whitebait consists of fry of many important food species (such as

herring Herring are forage fish, mostly belonging to the family of Clupeidae. Herring often move in large schools around fishing banks and near the coast, found particularly in shallow, temperate waters of the North Pacific and North Atlantic Ocean ...

sprat Sprat is the common name applied to a group of forage fish belonging to the genus '' Sprattus'' in the family Clupeidae. The term also is applied to a number of other small sprat-like forage fish ('' Clupeoides'', '' Clupeonella'', '' Corica'' ...

sardine "Sardine" and "pilchard" are common names for various species of small, oily forage fish in the herring family Clupeidae. The term "sardine" was first used in English during the early 15th century, a folk etymology says it comes from the It ...

mackerel Mackerel is a common name applied to a number of different species of pelagic fish, mostly from the family Scombridae. They are found in both temperate and tropical seas, mostly living along the coast or offshore in the oceanic environment. ...

bass Bass or Basses may refer to: Fish * Bass (fish), various saltwater and freshwater species Music * Bass (sound), describing low-frequency sound or one of several instruments in the bass range: ** Bass (instrument), including: ** Acoustic bass gui ...

and many others) it is not an ecologically viable foodstuff and in several countries strict controls on harvesting exist. * ''Elvers'' are young

eels Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

. Traditionally, fishermen consumed elvers as a cheap dish, but environmental changes have greatly reduced eel populations and the European eel is now critically endangered. ''Glass eels'' are even younger eels than elvers, the stage in the Eel life history when eels first arrive in rivers and swim upstream from the sea in which they hatched. Because the eel cannot be farmed, eels have instead been caught from the wild as juveniles and reared in captivity for human consumption, reducing the wild population further. Like whitebait, elvers are now considered a delicacy and are priced at up to 1000

euro The euro ( symbol: €; code: EUR) is the official currency of 19 out of the member states of the European Union (EU). This group of states is known as the eurozone or, officially, the euro area, and includes about 340 million citizens . ...

per kilogram. A small serving of Spanish ''angulas'', (literally: 'eels') for example, can cost the equivalent of US$100, and other species which can be purchased cheaply are prepared and eaten as "''angulas"'' instead. Glass eels are regularly smuggled out of Europe having been harvested illegally for Asian and Russian consumers; smugglers can earn millions of

pounds sterling Sterling (abbreviation: stg; Other spelling styles, such as STG and Stg, are also seen. ISO code: GBP) is the currency of the United Kingdom and nine of its associated territories. The pound ( sign: £) is the main unit of sterling, and ...

. Elvers reach a higher price in China than does beluga caviar. The

Marine Conservation Society The Marine Conservation Society is a UK based not-for-profit organization working with businesses, governments and communities to clean and protect the oceans. Founded in 1983, the group claims to be working towards "cleaner, better-protected, h ...

advises against buying European eels.

Notes

References

* ''Atlantic Salmon Trust'
Salmon Facts
Retrieved 15 December 2011. * Bley, Patrick W and Moring, John R (1988
Freshwater and Ocean Survival of Atlantic Salmon and Steelhead: A Synopsis"
''US Fish and Wildlife Service''. * Lindberg, Dan-Erik (2011
Atlantic salmon (Salmo salar) migration behavior and preferences in smolts, spawners and kelts
Introductory Research Essay, ''Swedish University of Agricultural Sciences''. {{Authority control Aquatic ecology Fish reproduction Ichthyology