What fish is it?

What fish is it?

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I bought this 2 weeks ago, but i forgot to ask the seller, what fish is it. Currently the size is 1 inch.

An African cichlid. Because it is apparently albino you may not find an exact match. Start looking under "apistogramma".

FISH Test (Fluorescence In Situ Hybridization)

Fluorescence in situ hybridization (FISH) is a test that “maps” the genetic material in a person’s cells. This test can be used to visualize specific genes or portions of genes. FISH testing is done on breast cancer tissue removed during biopsy to see if the cells have extra copies of the HER2 gene. The more copies of the HER2 gene that are present, the more HER2 receptors the cells have. These HER2 receptors receive signals that stimulate the growth of breast cancer cells.

The FISH test results will tell you that the cancer is either “positive” or “negative” (a result sometimes reported as “zero”) for HER2.

Generally, the FISH test is not as widely available as another method of HER2 testing, called ImmunoHistoChemistry, or IHC. However, FISH is considered more accurate. In many cases, a lab will do the IHC test first, ordering FISH only if the IHC results don’t clearly show whether the cells are HER2-positive or negative.

Research has shown that some HER2 test results may be wrong. This is probably because different labs have different rules for classifying positive and negative HER2 status. Each pathologist also may use slightly different criteria to decide whether the results are positive or negative. In most cases, this happens when the test results are borderline -- meaning they aren't strongly HER2-positive or HER2-negative.

In other cases, tissue from one area of a breast cancer can test HER2-positive and tissue from a different area of the cancer can test HER2-negative.

Inaccurate HER2 test results may cause women diagnosed with breast cancer to get less than the best care possible. If all or part of a breast cancer is HER2-positive but test results classify it as HER2-negative, doctors aren't likely to recommend medicines that work against HER2-positive breast cancers -- even though the woman could potentially benefit from those medicines. If a breast cancer is HER2-negative but test results classify it as HER2-positive, doctors may recommend anti-HER2 treatments -- even though the woman is unlikely to get any benefits and is exposed to the medicines' risks.

There are six medicines that work against HER2-positive breast cancer:

If your HER2 test results are HER2-negative, you may want to ask your doctor about how confident he or she is in the lab that did the HER2 testing and if another HER2 test might make sense for your unique situation.

If your HER2 test results are borderline, you might want to ask your doctor if more than one pathologist reviewed the results. If the HER2 test results weren't reviewed by more than one pathologist, you may want to ask if the results can be reviewed again.

FISH is best performed on tissue that has been preserved in wax or chemicals, rather than on fresh or frozen tissue.

About the Author

John D. Reynolds is a Professor of Evolutionary Ecology at the University of East Anglia, UK. His research examines the evolution of reproductive behaviour and life histories, with an emphasis on conservation of marine and freshwater fishes. He has co-authored a textbook, Marine Fisheries Ecology (2001), has co-edited Conservation of Exploited Species (2001) and is co-editor of the journal, Animal Conservation. He was awarded the FSBI medal of the Fisheries Society of the British Isles in 2000.

Essential Fish Biology: Diversity, structure, and function

This book summarizes the basic features of living fish. It is introduced by a chapter on the diversity of a group which has over 30,000 species, the largest within the vertebrates, describing the classification systems used for them and the variety of their habitats and morphology. Thereafter the physiology of fish is described and discussed initially by categories such as the outer boundary (the skin), the circulatory system, food processing, reproduction, hormones as integrators and controllers, the nervous system and the very complex set of sensory receptors including the eyes, ears, latera . More

This book summarizes the basic features of living fish. It is introduced by a chapter on the diversity of a group which has over 30,000 species, the largest within the vertebrates, describing the classification systems used for them and the variety of their habitats and morphology. Thereafter the physiology of fish is described and discussed initially by categories such as the outer boundary (the skin), the circulatory system, food processing, reproduction, hormones as integrators and controllers, the nervous system and the very complex set of sensory receptors including the eyes, ears, lateral line and electro-receptors. Unusual structures, adaptations and behaviours reveal the breadth of fish lifestyles from deep-ocean to shallow reef habitats, with both fresh water and marine margins favouring some near-terrestrial forms even emerging to spawn. With enormous ranges of size, shape and lifecycles, fish are capable of extreme longevity and amazing adjustments to their environment, including colour change, light emission by photophores and sporadic hermaphroditism (both sexes in one individual). The use of fish types by scientists is discussed. Referenced throughout, the scope of the book includes reviews of historically important and recent discoveries and some speculation on the future for fish and fish conservation. Appendices are provided to give in-depth information on some topics, including material briefly describing practical procedures, relevant to experimentation and aquaculture, which may prompt further investigation. The glossary with explanations of terms, and the copious illustrations help understanding of this complex subject area.

Bibliographic Information

Print publication date: 2017 Print ISBN-13: 9780198785552
Published to Oxford Scholarship Online: December 2017 DOI:10.1093/oso/9780198785552.001.0001


Affiliations are at time of print publication.

Derek Burton, author
Professor Emeritus, Department of Biology, Memorial University of Newfoundland, Canada

Margaret Burton, author
Professor Emeritus, Department of Biology, Memorial University of Newfoundland, Canada

Biology and Physiology of Freshwater Neotropical Fish

Biology and Physiology of Freshwater Neotropical Fish is the all-inclusive guide to fish species prevalent in the neotropical realm. It provides the most updated systematics, classification, anatomical, behavioral, genetic, and functioning systems information on freshwater neotropical fish species. This book begins by analyzing the differences in phylogeny, anatomy, and behaviour of neotropical fish. Systems such as cardiovascular, respiratory, renal, digestive, reproductive, muscular, and endocrine are described in detail. This book also looks at the effects of stress on fish immune systems, and how color and pigmentation play into physiology and species differentiation.

Biology and Physiology of Freshwater Neotropical Fish is a must-have for fish biologists and zoologists. Students in zoology, ichthyology, and fish farming will also find this book useful for its coverage of some of the world’s rarest and least-known fish species.

Biology and Physiology of Freshwater Neotropical Fish is the all-inclusive guide to fish species prevalent in the neotropical realm. It provides the most updated systematics, classification, anatomical, behavioral, genetic, and functioning systems information on freshwater neotropical fish species. This book begins by analyzing the differences in phylogeny, anatomy, and behaviour of neotropical fish. Systems such as cardiovascular, respiratory, renal, digestive, reproductive, muscular, and endocrine are described in detail. This book also looks at the effects of stress on fish immune systems, and how color and pigmentation play into physiology and species differentiation.

Biology and Physiology of Freshwater Neotropical Fish is a must-have for fish biologists and zoologists. Students in zoology, ichthyology, and fish farming will also find this book useful for its coverage of some of the world’s rarest and least-known fish species.

Interesting Insights from the Oscar Fish!

While the oscar is a commonly kept aquarium fish, many owners are not aware of the amazing biological concepts their fish displays. In fact, the oscar is a perfect example of the following concepts!

Suction Feeding

Oscar fish – like many other predatory fish – use the viscosity of water to their advantage. Unlike air, which moves freely around objects, water is much denser. Plus, water molecules pull on each other through the process of cohesion. So, when the oscar opens its mouth quickly, a massive wall of water is sucked in.

Smaller fish unlucky enough to be caught in the wave are pulled into the oscar’s mouth, with no hope of escaping. Besides fish, many other aquatic organisms use suction feeding to their advantage. Notable suction feeders include some species of shark, newts, catfish, and many others. Suction feeders are typically “ambush predators” – waiting carefully for their prey to come close enough to be caught in the suction vortex!

Invasive Aquarium Fish

The oscar fish is not the only fish that has expanded its range since it has been commonly kept as an aquarium species. Unfortunately, the aquarium industry has introduced many invasive species into natural environments around the world. While the environmental impact of oscar fish releases has not been well studied, other aquarium species that have been released are wreaking havoc on natural environments.

For example, the Zebrafish is a commonly kept saltwater aquarium species. The fish is beautiful, colorful, and very interesting to watch in captivity. For this reason, the fish was imported to the United States from its native range in the Indian Ocean. However, a few Zebrafish were accidentally released into the Gulf of Mexico. Only a few decades later, the Zebrafish has become a massively destructive species along many reefs in the Gulf.

Since the Zebrafish is a voracious predator and has a number of protective spines, it can eat almost everything and has no natural predators in the Gulf of Mexico. As such, Zebrafish populations have exploded and are rapidly depleting many fish species important to the health of the coral reef. In fact, this invasive species is so destructive that is has been partially blamed for the loss of corals from South America to Florida.

Brood Care

Though the oscar is a voracious predator, these fish can also make very protective parents. Oscar fish naturally defend their territory, chasing off all other fish that come too close and eating anything small enough to fit in their large mouths!

However, when it comes to their babies, oscars are very careful. In fact, the oscar fish will protect its babies and is very careful not to suck them up. This is known as “brood care” and is a type of parental care seen in several fish species. While most fish simply release their eggs into the environment, the oscar will protect its offspring until they are large enough to leave and established their own territory.

Handbook of Fish Biology and Fisheries , Том 1

The Handbook of Fish Biology and Fisheries has been written by an international team of scientists and practitioners, to provide an overview of the biology of freshwater and marine fish species together with the science that supports fisheries management and conservation.

This volume, subtitled Fish Biology, reviews a broad variety of topics from evolutionary relationships and global biogeography to physiology, recruitment, life histories, genetics, foraging behaviour, reproductive behaviour and community ecology. The second volume, subtitled Fisheries, uses much of this information in a wide-ranging review of fisheries biology, including methods of capture, marketing, economics, stock assessment, forecasting, ecosystem impacts and conservation.

Together, these books present the state of the art in our understanding of fish biology and fisheries and will serve as valuable references for undergraduates and graduates looking for a comprehensive source on a wide variety of topics in fisheries science. They will also be useful to researchers who need up-to-date reviews of topics that impinge on their fields, and decision makers who need to appreciate the scientific background for management and conservation of aquatic ecosystems.

Respiration in Fish

Respiration is a biochemical process by which food in the cell is oxidized with the help of oxygen to produce energy and carbon dioxide (CO2) is released as a by-product. All kinds of biological function require such energy. Carbohydrates are mainly involved in energy production. In the absence of carbohydrates, this energy is produced by oxidizing fats and proteins. This reaction is shown below through chemical equations.

Respiration is a feature of life and an indicator of all biochemical activities in the body. Respiration involves the exchange of two gases, oxygen (O2) and carbon dioxide (CO2). The respiratory system is made up of all the organs that are involved in the function. Based on the presence of oxygen, respiration is divided into aerobic and anaerobic.

In aerobic respiration, free oxygen is taken from the environment and carbon dioxide is emitted as energy is produced. This type of respiration occurs in most plants and animals. Organisms that breathe this way are called aerobes. Lactic acid is produced when glucose is metabolized in anaerobic respiration. In this case, no oxygen is required and no carbon dioxide is formed. Such respiration occurs in certain bacteria, parasites, etc. Such organisms are called anaerobes. The absence of oxygen in an organism is called anaerobiasis.

Like other animals, adequate oxygen supply is required to fish tissues for oxidataion and energy production. A respiratory organ has formed in animals to receive oxygen for intracellular oxidation and to sustain life and to emit carbon dioxide.

Oxygen and carbon dioxide are exchanged between blood and water (air) through the respiratory organs. This type of breathing is called exhalation. Through the exchange of blood and body tissues and gases, energy is generated in the cell which is called inhalation.

In most animals, the presence of special organs to control respiration can be observed. The respiratory system is made up of these organs. There are four main types of respiratory organs in the animal kingdom. These are:

Fish have well-developed respiratory organs. The physiological processes of respiration of different fish are roughly similar to those of the upper vertebrae. However, there are differences in the respiratory organs. Fish are the main aquatic vertebrates and take up most of the dissolved oxygen from the water. Some fish have the ability to breathe air. The gills are the main respiratory organs of fish. However, some bony fish have respiratory organs that help them breathe air. In air breathing fish, gills play a complementary role. As an efficient respiratory organ, the gill can use up to 70% of the dissolved oxygen in the water flowing through it. In humans, 25% of the oxygen in the lungs can enter the pulmonary cavity. The ability of the gills as a respiratory organ in fish depends on two factors, viz

1. The nature of the gill structure and capillary blood vessels

2. Immerse the gills in a running stream of water so that fresh oxygen can always come in contact with the gills.

Location of Gills in Fishes

A row of vertical opening in the side wall of the pharynx indicates the presence of gills. Each pharyngeal opening enters a flattened gill pouch that connects to the outside through the gill openings. The gill pouches are separated by interbranchial septum. These septum or interstices carry gill filaments to its opposite wall. At the tip of the head, between the eyes and the thoracic fins, there is an external gill openings.

The gill openings are usually small, but in the Cetorhinus (huge basking shark), the openings are very large, extending from the top to the bottom of the body. Other gill openings are located in the posterior branchial arches. Most cartilaginous fish have five gill openings on each side in addition to the spiracle, but some sharks, such as the Hexanchus, have six gill openings except the spiracle, and the Heptranchias have seven pairs of gill openings.

In most cartilaginous fish, especially sharks, the gill pouch is exposed to the outside through individual external gill openings, and the gill openings are covered by posterior dermal folds.

Bony fish have interpharyngeal gill openings but they are not individually exposed to the outside. All of these openings are exposed to a common branchial chamber that is covered by a movable operculum. Each branchial chamber is exposed outside by a large opening. Opercula of the two sides overlap or merge. In some Actinopterigians, the rate of convergence of this overlaping is so high that the opercular opening is reduced to a small bilateral round opening (e.g. eel fish).

The operculum consists of four broad and flattened bones that may or may not have long branchiostegal rays on the ventral side. Among cartilaginous fish, operculum is present in Holocephali. This structure of oparculam in this fish is the interstitial condition of cartilaginous and bony fish. In this case, the actual interbranchial septum is smaller and the gills are in a normal branchial chamber. On the outside of this chamber, like the operculum of bony fish, it is covered by a skin-like fringe. Each branchial chamber is exposed outside through an opening. The bony fish has four gills on each side of its head. These gills are covered by operculum or gill covers which are exposed on the outside by an opening.

Types of Gills

There are two types of fish gills based on location, viz

(1) Internal gills- In this case, the gills are placed inside the gill pouch (shark) or inside the branchial chambers (holocephalan and bony fish).

(2) External gills - External gills develop in many fish for respiration in the larval stage. On the basis of development, it is again divided into two types, viz

(a) True external gills - They do not depend on the internal gills but develop as a result of development of skin. In the larval stage, Polypterus and Lepidosiren have true external gills. The number here is four pairs. This external gill becomes extinct as it matures, but at the the adult stage, Protopterus also contains external gill remains. In Polypterus, leaf-like external gills are present located on the gill opening.

(b) Prolongation from the internal gills: This type of gill is formed by elongating the inner gill-filament and it is located outside the body. Such gills are found in some Selachian and embryos of some oviporous bony fish. Long fibrous external gills are made up of from the wall of the gill opening of embryos in cartilaginous fish. Sea water flows through such type of fibrous structures and plays a role in respiration.

In the viviparous cartilaginous fish (Selachian), these organs also participate in the absorption of nutrients. In the larval stage of some oviparous bony fish (Gymnarchus, Clupisdis) and other fish it plays a role in respiration. In the Gymnarchus, a thin fibrous growth is formed from the opercular end of the internal gills and acts as an external gills.

The gill is divided into four types based on its structure and function, viz

(1) Hemibranch: The gill pouches are separated by the interbranchial septum. The front and back walls of each septum carry rows of gill filaments. The row of gill filaments on one side of the interbranchial septum is called the hemibranch. Hemibranch is divided into two types, viz

(a) Mandibular Hemibranch: The mandibular hemibrunch usually helps to close the spiracle and it receives oxygenated blood. The mandibular hemibranch regulates blood pressure in the ophthalmic arteries by increasing the oxygen concentration in the blood of the brain and acts as an endocrine gland. Most of it is made up of acidophilic cells. In the Lepisosteus, the mandibular pseudobranch and the hyoidian hemibranch are very close together and it receives blood from the afferent hyoidian artery and the 1st gill arch efferent artery. In sturgeon (Acipenser), there is no contact between mandibular pseudobranch and hyoidian hemibranch. In Amia, there is no direct contact between the pseudobranch and the effernet or afferent blood vessels. In this case, the pseudobranchial blood vessel connects the orbital and ophthalmic blood vessels. Polypterus does not have mandibular pseudobranch.

(b) Hyoidean Hemibranch: Most fish have such gills. Most gills of Elasmobranchii are of the hemibranch type. In shark, each gill arch holds one afferent and two efferent blood vessels. In this case, 5-7 pairs of gill pouches are arranged on each side of the head and in Rays (Rajifornes) it is arranged in a linear direction. Sharks and Rays have an extra opening, called a spiracle. It has no role in respiration. In Selachian, it is extinct or bud like. In holocephalan, it is adjacent to the operculum. Most Actinopterygii do not have it. Acipenser, Lepisosteus, Polyodon and Amia have such gills. In Scaphirhinchus, it is greatly reduced. Polyopterus has mandibular pseudobrach and hyoidian hemibranch. Other crossopterygian (except Lepidosiren) have hyoidian hemibranch. In Latimaria it is small.

(2) Pseudobranch: When the hemibranch loses its actual respiratory capacity, it is called a pseudobranch. Many Actinoterigians, such as the Catla catla, have a hyoidian pseudobranch with a single gill filament in front of the first gill.

The pseudobranch is covered by free or single-layered mucous membranes. It develops entirely in the early embryonic stage and in the embryonic stage, it plays a role in respiratory function but in adulthood, it has no role in respiration. It receives oxygenated blood directly from the dorsal aorta and it has contact with the intra-carotid artery and blood vessels. It increases the concentration of oxygen in the blood and travels through the intra-carotid arteries to the brain and eyes, such as Wallago attu, Mystus aor, Notopterus notopterus, Channa.

In trout, it has a comb-like structure. In the case of perch, it is covered by a highly depleted pharyngeal epithelium. In Cod fish, pseudobranch are completely covered by the pharyngeal epithelium and form a glandular organ called the rete mirabile. Although it originates from the depths of the pharyngeal tissue, it also originates from the fine formation of glandular tissue. In the case of Amia, it is reduced and covered by the pharyngeal mucous epithelium. Pseudobranch plays an important role in filling the swimbladder and controlling intraocular pressure.

(3) Holobranch: When an entire gill consists of two hemibranch, it is called a holobranch. The holobranch contains an interbranchial septum (reduced in advanced fish) of which the front and back wall contain gill filaments with rich capilary blood vessels. An entire gill or a holobranch consists of cartilage or bony gill arch. Each arch has gill rakers on the inside and plate-shaped filaments with rich in blood vessels on the outside.

Elasmobranch usually have 5 pairs of gill openings but bony fish have 4 pairs of gill openings and there are no spiracles. The teleost develops a single external branchial opening, forming an operculum covering the gills on each side of the head. These fish have a decrease in the interbranchial septum and the conjunctival efferent branchial artery of the elasmobranch has become a single efferent blood vessel.

(4) Lophobranch: Sea horse (Hippocampus) and pipe fish (Syngnathus) have reduced gill filament which form a rosette-like hair follicle structure. These clusters are associated with small reduced gill arches. Such gills are called cluster gills or lophobobranch.

Gills of Different Fishes

The number, location and function of gills vary in different fishes. The following are the descriptions of gills in the major fish groups:

Gills of Lamprey (Petromyzonidae)

There are 6 pairs of gills on each side of the lamprey. These gill pouches are released into the pharyngeal cavity. Each pouch is divided by a diaphragm adjacent to the body wall. In addition to the diaphragm on the inner edge, the gill pouch has radially arranged gill filament which has small folds from one end to the other, increasing the respiratory level. The gill pouches have a cartilaginous structure, called branchial baskets. Through this, communication with the outside is achieved through the gill opening in the gill chamber.

Lamprey lives as parasite most of the time, so they do not use sucking mouths to breathe because they are attached to host fish or other objects such as rocks. In the lamprey, water enters the respiratory tract through the gill pouch and exits in the same way. In marine lampreys, the gill pouch is seen to contract and expand 50-70 times per minute while it is attached to the prey, but in river lampreys (Lampetra fluviatilis) it is seen to be 120 to 200 times per minute.

Respiratory water enters the gill pouch through the flow of water and the water is expelled by the contraction of the branchial compressor muscle adjacent to the branchial basket and the division of the inside of the pouch and the contraction of the sphincter around each gill opening. Water also enters through the contraction and dilation of the nasopharyngeal sac.

Gills in Hagfish (Myxiniformes)

In this case, the gills are transformed into gill pouch. The pouch of gill region are exposed in the pharynx. They have 6-15 pairs of gills. Myxine contains 6 pairs of gill pouch. These pouches are not exposed to the outside through an opening like lamprey, and each pouch forms a long emission tube. The 6 emission tube on each side then join together to form a common tube and are exposed to the outside through a single gill opening.

Gills in Cartilaginous Fish

In the gill pouch, there is a respiratory organ called gills. In different sharks, structure of gill pouches are of different types. They have 5 pairs of gill pouch on the lateral side of their head. Each gill pouch maintains communication with the pharynx through single intra-branchial openings and 5 external gill openings.

A row of horizontal branchial lamellae is produced from the lining of the mucous membrane of the gill pouch. These lamellae are enriched with excessive amounts of blood vessels. At the front or each gill pouch, there is a set of branchial lamellae and at the back, another set at of branchial lamellae. The gill pouches are separated by the interbranchial septum. The interbranchial septum tends to be longer in length than the branchial or gill lamellae. Each interbranchial septum has one visceral arches at the pharyngeal end.

The back of each arch carries the anterior lamellae of gill pouch and the rear set lamellae of the next gill pouch. The first gill pouch is between the hyoid and the 1st bronchial arch and the 2nd gill is located between the 1st and 2nd branchial arches, the 3rd gill pouch is located between the 2nd and 3rd branchial arches, the 4th gill pouch is located between the 3rd and 4th bronchial arches and 5 th gill pouch is between 4 th and 5 th branchial arches. Two types of gills can be seen in sharks- Namely:

1. Holobranch: This type of gill has 2 sets of gills or gill lamellae. That is why they are called complete gills or holobranch. The first 4 branchial arches carry holobranch.

2. Demibranch or hemibranch: This type of gill has a set of gills or gill lamellae. The hyoid arch carries a single hemibranch. The last branchial arch has no gills. During the respiration, the floor of the buccal cavity goes down or down and the mouth is exposed. Then water enters at a rapid rate and fills the overly stretched buccal cavity. Immediately after this, the mouth and pharynx become constricted. As a result, the water then enters the gill pouch and after exchanging the gas, the gill comes out through the gill opening. When the mouth is engaged in other work (catching prey), the spiracle provides a helpful pathway to enter water for the respiration.

Gills in Bony Fish

In this case, there are four pairs of gills on the back of the head, four on each side. The gills on each side are covered by gill covers or oparculam. The following is a description of the structure of gills:

The main respiratory organ or the ideal structure of the gills

The gills are the main respiratory organs of fish. There is a row of crevice-like openings in the side wall of the pharynx, the first of which is called a spiracle. It is located between the mandibular and the hyoid arch. The second or hyoidean cleft is located between the hyoid arch and the first branchial arch. The remaining gill openings are located between the posterior branchial arches. From the anterior and posterior walls of each gill opening, a blood-rich, fibrous outgrowth is produced where dissolved oxygen and carbon dioxide are exchanged. In addition to gills, skin and swimbladder act as respiratory organs.

Each gill structure looks like a comb and its gill arch has rows of gill filaments. Each gill arch carries two rows of gill filaments. The surface of each gill filament has numerous small folds that increase the overall surface area of the gill for gas exchange. The respiratory area of the fish gills depends on the size and number of gill filaments. Respiratory areas are developed based on fish habits. In fish, the principle of respiration of gill is almost the same.

Structure of a Teleostean Gill

The teleost usually has four pairs of gills. Each gill has a large lower wing and a smaller upper wing which are mainly composed of seratobranchial and epibranchial. An ideal gill of a fish consists of the following parts:

(1) Gill Raker: Gill raker develops at the inner edge of the gill arch. This is the modification of the dermal denticle. It is arranged in two rows. Depending on the diet and eating habits, it can be soft, thin thread-like or hard, flat and triangular or even tooth-like. Each raker is externally covered by an epithelial lining with taste buds and mucus-secreting cells. These taste buds help the fish to understand the chemical nature of the water flowing through the gill opening. The gill rakers are more developed in fish that eat small creatures.

The gill-filament is likely to be damaged or ineffective as small organisms enter through the enternal gill opening during swimming. Typically, gill rakers form a sieve-like structure through which water flows over the gills and filters out the water and protects the brittle gill filaments from solid particles. Different fish show differences in structure of this gill raker.

In plankton-eating fish such as Tenualosa ilisha, Gadusia, Goniolosa, Notopterus, Hypophthalmicthyes, the gill rakers combine to form a filter. Many strainers carry the second and third stage branches of the primary gill rakar and form a dense net. In pike fish (Esox), the gill raker is reduced to form small bony structure which prevent large particles from entering. In closely related species, the formation and numerical differences of the gill rakars are observed.

The mature Alosa alosa has about 80 gill rakar at the bottom of the arch and the Alosa fallax has 30 gill rakar. In Cetorhinus (Basking shark) and Rhinocodon (whale shark), the length of gill rakars are 10-12 cm. In whales, these gill rakars are flattened and functionally formed into baleen plates. Other sharks do not usually have gill rakar. It has been reduced in crossopterygians.

(2) Gill Arch: Each gill arch is surrounded by an efferent and afferent branchial blood vessel and nerve. It is externally surrounded by numerous mucous glands, eosinophilic cells and a thick or thin epithelium with taste buds. Fish living in different ecological habitats vary in number and extent of mucus glands and taste buds. Each gill arch consists of at least one set of abductor and one set of adductor muscles that play a role in the movement of the gill filament (primary lamellae) during respiration.

The abductor muscles attach to the proximal edge of the gill ray from the outside of the gill arch. The adductor muscle resides in the interbranchial septum and enters the opposite gill-ray by crossing each other. There are two known types of adductor muscles and their arrangement. In some teleosts such as Channa striatus, Rita rita, the adductor muscle is generated from the base of the gill-ray on one side and enters the gill-ray on the other side obliquely. In some other species such as Labeo rohita, Tenualosa ilisha, Cyprinus carpio, due to the enlargement of the interbranchial septum, this muscle is generated halfway through the gill-ray and adjacent to the gill-ray on the other side.

(3) Gill filament or primary lamellae: Each gill arch has a two rows of gill filament or primary gill lamellae which are placed outside of the pharyngeal cavity. In most teleosts, the interbranchial septum between the two rows of lamellae is shorter, so the two rows of lamellae are exposed at their distal ends. In Labeo rohita and Tenualosa ilisha, the septum extends to the lower half of the primary lamellae. Due to the diversity of foods, the size, shape and number of primary lamellae vary in different fish.

Species that live actively and rely entirely on aquatic respiration (such as Catla catla, Cirrhinus mrigala, Wallago attu, Mystus seengala) have numerous long gill filaments. However, fish that live inactive or have aerial respiratory organs that have few and and reduced filaments. The gill lamellae consist of two hemibranch that alternate with each other (e.g. Labeo rohita) or they may be attached to the gill arch (Channa striatus).

Usually the gill lamellae in each row are independent of each other. In Labeo rohita, however, the lamellae are consolidated from the base to the tip, and they have narrow crevice-shaped openings. In some river fish, the primary gill lamellae re-divide and form additional lamellae. The lamellae can split in the middle or from the base to form two branches.

Sometimes three to four branches combine to form numerous branches which can form a flower-like structure at one end. The gill ray gives a strong structure to the primary gill lamellae. The gills are composed of partial bones and partial cartilage which are connected to the gill arch and are attached to each other by fibrous ligaments. Each gill ray is divided into two branches. Its nearest edge forms a pathway to the efferent branchial blood vessels.

(4) Secondary Lamellae: Each primary lamellae or gill filament has numerous secondary lamellae on either side. These lamellae have a flattened, leaf-like structure that serves as the main field of gas exchange. Depending on the species living in different ecological habitats, their shape, size and density depend on the unit length of the gill filament. Secondary lamellae are usually free from each other but may merge at the distal end of the primary lamellae.

There are 10-40 secondary lamellae on each side of the primary lamellae. They are numerous in active species. Each secondary lamellae has a central blood vessels rich organs consisting of columnar cells and is surrounded by a basal membrane and the external epithelium. In some fish, this lamellar epithelium is smooth, but other fish it is uneven and has microridge and microvilli.

The epithelium on the surface of the secondary lamellae has grooves and ridges that contribute to increase the respiratory level. One of the structural features of the teleost gill is the presence of columnar cells that are separated by an epithelial covering on the other side of a lamella. Each cell has a central part with an extended part at each end. These enlarged parts are called piller cell flanges that overlap the surrounding cells and form a wall of blood vessels in the lamella. The pillars of the base membrane material connect the secondary lamellae horizontally to the base membrane on the other side and give a structural firmness to the secondary lamellae.

Studies have shown that columnar cells in each row of Channa form a complete divider between blood vessels. Such a system helps in the formation of a narrow water flow and can create reverse flow of blood and water at the microcirculatory level. These columnar cells prevent the contraction and expansion of the blood-rich space and regulate the type of blood flow through the secondary lamellae.

(5) Gill area: The relative number and size of gill lamellae determine the respiration area of the fish's gills. The overall gill area of a fish species is determined by the overall length of the primary lamella, the number of secondary lamellae, and the average bilateral lamella region. The overall respiration area varies depending on the fish habitat. Generally faster swimming fish have more gill regions and per mm than inactive species. The gill filament contains numerous gill lamellae. Half of the gill area of aerial respiratory fish is directly proportional to the gill permeability efficiency.

During the physical growth of the fish, as the body weight increases, the filtration efficiency of the gill increases. The efficiency of the gill as a respiratory organ also depends on the distance of diffusion. For this reason, obstruction of gas exchange occurs between blood and water. This obstruction is made up of lamellar epithelium, basal membranes, and columnar cell flanges, and it is less common in aquatic respiratory fish than in aerial respiratory fish.

Aquatic respiratory fish have higher diffusion efficiency due to larger gill regions and shorter diffusion distances. However, aerial respiratory fish have a shorter gill area and a wider diffusion distance. According to Saxena (1958), the gill area is much smaller in aerial respiratory fish such as Heteropneustes and Clarias than in aquatic respiratory fish.

Groups of Fish

Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata

2 Classes of Jawless fish:
- Lamprey (parasitic)
- Hagfish (scavenger)
- Both have cartilage skeleton

Class Chondrichthyes

- Cartilage Fish
- Sharks, stingrays
- Most are predators
- Basking sharks are filter feeders
- No swim bladder, pectoral fins rigid

Class Osteichthyes

- Bony Fish
- Ray-finned ( Goldfish, Bass, Carp, Salmon )& Lobe Finned ( Coelacanth )

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Deep-sea fish

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Deep-sea fish, in general, any species of fishes (class Osteichthyes) that are found at extreme ocean depths, usually more than 600 m and even to as much as 8,370 m (that is, about 2,000 to 27,500 feet). Mid-water species, which represent more than a dozen families of marine fishes, are characterized by huge mouths, enlarged eyes, and the presence of luminous organs on some or several parts of the body. The light-producing organs serve to attract either prey or potential mates. These and other peculiar traits of deep-sea fishes represent evolutionary adaptations to the extreme pressure, cold, and particularly the darkness of their environment. The fish life of the deep-sea habitat is among the most specialized of any habitat in the world.

The most important groups of mid-water deep-sea fishes are the deep-sea angler fishes (belonging to the suborder Ceratioidei), which lure prey within reach by dangling their extended dorsal fin spines as bait the viperfishes (family Chauliodontidae), whose numerous fanglike teeth make them awesome predators and the bristlemouths (family Gonostomatidae), which are among the most abundant fishes in the world.

In contrast, bottom-living (benthic) forms have smaller eyes and smaller, often down-turned, mouths, and they usually lack luminous organs. They include the grenadiers (family Macrouridae), batfishes (family Ogcocephalidae), and cusk eels (family Ophidiidae).

This article was most recently revised and updated by Richard Pallardy, Research Editor.


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