Spotted rat fish

Introduction:

The spotted ratfish, Hydrolagus colliei, is a chimaera found in the north-eastern Pacific Ocean. Often seen by divers at night in the Pacific Northwest, this harmless shark relative gets its characteristic name from a pointed rat-like tail. The ratfish lays leathery egg cases on the bottom of muddy or sandy areas which are often mistaken by divers as something inanimate. While mainly a deep-water species, it occurs at shallower depths in the northern part of its range. The generic name, Hydrolagus, comes from the Greek words "hydro", meaning water, and "lagus", meaning hare, and the specific name honors Alexander Collie, who was a ship surgeon and early naturalist. The ratfish is not typically eaten by humans and is not commercially caught.


Diet:
The spotted ratfish swims slowly above the seafloor in search of food. Location of food is done by smell. Their usual hunting period is at nighttime, when they move to shallow water to feed. Spotted ratfish are particularly drawn to crunchy foods like crabs and clams. Besides crabs and clams, the spotted ratfish also feeds on shrimp, worms, small fish, small crustaceans, and sea stars. Species known to predate on the spotted ratfish include soupfin sharks, dogfish sharks, Pacific halibut, and Pigeon guillemots.

Reproduction:

Like some sharks, spotted ratfish are oviparous. Their spawning season peaks during the spring to autumn months. During this time, the female releases up to two fertilized eggs into sand or mud areas of the seabed every 10 to 14 days. The extrusion process can last anywhere from 18 to 30 hours and the actual laying can last another four to six days. The egg sack is leather-like, five inches long, and has a filament connected to it which is used to attach it to the ocean floor when it is let go by the mother. It is not unheard of to see a female ratfish swimming around her newly laid eggs, in hopes of preventing predators from finding them. Development of the egg can take up to a year, which can be dangerous because the eggs are sometimes mistaken for inanimate objects by divers. When the young finally hatch, they are about 5.5 inches (14 cm) in length and grow, reaching 11.8 inches (30 cm) in length their first year.

Ballyhoo fish

Introduction:

he ballyhoo or bally, Hemiramphus brasiliensis, is a baitfish of the halfbeak family (Hemiramphidae). It is similar to the Balao halfbeak (Hemiramphus balao). Ballyhoo are frequently used as cut bait and for trolling purposes by saltwater sportsmen.

Ballyhoo can also be seen above the waters skimming the surface to escape from their predators. The appearance is similar to skipping stones on the water.The name ballyhoo comes from the native Brazilian Tupí–Guaraní term "b'ayi hyo" meaning "penis fish"

Puffer fish (Tetraodontidae)

Introduction:

Tetraodontidae is a family of primarily marine and estuarine fish of the orderTetraodontiformes. The family includes many familiar species, which are variously calledpufferfish, puffers, balloonfish, blowfish, bubblefish, globefish, swellfish, toadfish,toadies, honey toads, sugar toads, and sea squab.They are morphologically similar to the closely related porcupinefish, which have large external spines (unlike the thinner, hidden spines of Tetraodontidae, which are only visible when the fish has puffed up). The scientific name refers to the four large teeth, fused into an upper and lower plate, which are used for crushing the shells of crustaceans and mollusks, their natural prey.

Pufferfish are generally believed to be the second-most poisonous vertebrates in the world, after the golden poison frog. Certain internal organs, such as liver, and sometimes the skin, contain tetrodotoxin and are highly toxic to most animals when eaten; nevertheless, the meat of some species is considered a delicacy in Japan (as 河豚, pronounced as fugu), Korea (as 복 bok or 복어), and China (as 河豚 hétún) when prepared by specifically trained chefs who know which part is safe to eat and in what quantity.

The Tetraodontidae contain at least 120 species of puffers in 19 genera.They are most diverse in the tropics, relatively uncommon in the temperate zone, and completely absent from cold waters. They are typically small to medium in size, although a few species can reach lengths of greater than 100 cm.

Reproduction and evolution:

Many marine puffers have a pelagic, or open-ocean, life stage. Spawning occurs after males slowly push females to the water surface or join females already present. The eggs are spherical and buoyant. Hatching occurs after roughly four days. The fry are tiny, but under magnification have a shape usually reminiscent of a pufferfish. They have a functional mouth and eyes, and must eat within a few days. Brackish-water puffers may breed in bays in a similar manner to marine species, or may breed more similarly to the freshwater species, in cases where they have moved far enough upriver.

Reproduction in freshwater species varies quite a bit. The dwarf puffers court with males following females, possibly displaying the crests and keels unique to this subgroup of species. After the female accepts his advances, she will lead the male into plants or another form of cover, where she can release eggs for fertilization. The male may help her by rubbing against her side. This has been observed in captivity, and they are the only commonly captive-spawned puffer species.

Target-group puffers have also been spawned in aquariums, and follow a similar courting behavior, minus the crest/keel display. However, eggs are laid on a flat piece of slate or other smooth, hard material, to which they adhere. The male will guard them until they hatch, carefully blowing water over them regularly to keep the eggs healthy. His parenting is finished when the young hatch, and the fry are on their own.
The tetraodontids have been estimated to diverge from diodontids between 89 and 138 million years ago. The four major clades diverged during the Cretaceous between 80 and 101 million years ago. The oldest known pufferfish genus is Eotetraodon, from the Lutetian epoch of Middle Eocene Europe, with fossils found in Monte Bolca and the Caucasus Mountains. The Monte Bolca species, E. pygmaeus, coexisted with several other tetraodontiforms, including an extinct species of diodontid, primitive boxfish (Proaracana and Eolactoria), and other, totally extinct forms, such as Zignoichthys and the spinacanthids.

Poisioning:

Pufferfish can be lethal if not served properly. Puffer poisoning usually results from consumption of incorrectly prepared puffer soup, fugu chiri, or occasionally from raw puffer meat, sashimi fugu. While chiri is much more likely to cause death, sashimi fugu often causes intoxication, light-headedness, and numbness of the lips, and is often eaten for this reason.^{[citation needed]} Pufferfish tetrodotoxin deadens the tongue and lips, and induces dizziness and vomiting, followed by numbness and prickling over the body, rapid heart rate, decreased blood pressure, and muscle paralysis. The toxin paralyzes diaphragm muscles and stops the person who has ingested it from breathing. People who live longer than 24 hours typically survive, although possibly after a coma lasting several days.

The source of tetrodotoxin in puffers has been a matter of debate,but it is increasingly accepted that bacteria in the fish's intestinal tract are the source.

Saxitoxin, the cause of paralytic shellfish poisoning and red tide, can also be found in certain puffers.

Hammerhead fish

Introduction:

The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna while the winghead shark is placed in its own genus,Eusphyra. Many not necessarily mutually exclusive functions have been proposed for the cephalofoil, including sensory reception, maneuvering, and prey manipulation. Hammerheads are found worldwide in warmer waters along coastlines and continental shelves. Unlike most sharks, hammerheads usually swim in schools during the day, becoming solitary hunters at night. Some of these schools can be found near Malpelo Island in Colombia, Cocos Island off Costa Rica, and near Molokai Island in Hawaii. Large schools are also seen in southern and eastern Africa.The known species range from 0.9 to 6 m (3.0 to 20 ft) long and weigh from 3 to 580 kg (6.6 to 1,300 lb). They are usually light gray and have a greenish tint to them. Their bellies are white which allows them to be close to the bottom of the ocean and blend in to sneak up on their prey.Their heads have lateral projections which give them a hammer-like shape.


Reproduction:

Reproduction only occurs once a year for hammerhead sharks and usually occurs with the male shark biting the female shark violently until she agrees to mate with him.The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Like other sharks, fertilization is internal with the male transferring sperm to the female through one of two intromittent organscalled claspers. The developing embryos are at first sustained by a yolk sac. When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta (called a "yolk sac placenta" or "pseudoplacenta"), through which the mother delivers sustenance until birth. Once the baby sharks are born, they are not taken care of by the parents in any way. There is usually a litter of 12 to 15 pups; except for the Great Hammerhead which births litters of 20 to 40 pups. These baby sharks huddle together and swim toward warmer water and stay together until they are older and big enough to be on their own.

In 2007, the bonnethead shark was found to be capable of asexual reproduction via automictic parthenogenesis, in which a female'sovum fuses with a polar body to form a zygote without the need for a male. This was the first shark known to do this.

Diet:

Hammerhead sharks are known to eat a large range of items including fish, squid, octopus, crustaceans, and other sharks. Stingrays are a particular favorite. These sharks are often found swimming along the bottom of the ocean, stalking their prey. Their unique head is used as a weapon when hunting down prey. The hammerhead shark uses its head to pin down stingrays and eats the ray when the ray is weak and in shock. The Great Hammerhead, tending to be larger and more aggressive than most hammerheads, occasionally engages in cannibalism, being known to eat other hammerhead sharks, including their own young.

Blob fish

Introduction:

The blobfish (Psychrolutes marcidus) is a deep sea fish of the family Psychrolutidae. It inhabits the deep waters off the coasts of mainland Australia and Tasmania, as well as the waters of New Zealand.

Blobfish are typically shorter than 30 cm. They live at depths between 600 and 1,200 m (2,000 and 3,900 ft) where the pressure is several dozen times higher than at sea level, which would likely make gas bladders inefficient for maintaining buoyancy. Instead, the flesh of the blobfish is primarily a gelatinous mass with a density slightly less than water; this allows the fish to float above the sea floor without expending energy on swimming. Its relative lack of muscle is not a disadvantage as it primarily swallows edible matter that floats in front of it such as deep-ocean crustaceans.

Blobfish are often caught as bycatch in bottom trawling nets. Scientists now fear the blobfish could become an endangered species because of deep-ocean trawling.

Popular culture:

Due to its low density flesh, the blobfish's shape is very different when it is out of water. Its so called ugliness has created a lot of discussion in media outlets.

The musician and author Michael Hearst featured a composition titled "Blobfish," inspired by the animal, on his 2012 album Songs For Unusual Creatures.

In September 2013 the blobfish was voted the "World's Ugliest Animal," based on photographs of decompressed specimens, and adopted as the mascot of the Ugly Animal Preservation Society, in an initiative "dedicated to raising the profile of some of Mother Nature’s more aesthetically challenged children.

Oscar fish

Introduction:

Astronotus ocellatus is a species of fish from the cichlid family known under a variety of common names, including oscar, tiger oscar, velvet cichlid, or marble cichlid.In South America, where the species naturally resides, A. ocellatus specimens are often found for sale as a food fish in the local markets.The fish can also be found in other areas, including China, Australia, and the United States. It is considered a popularaquarium fish in the U.S

Taxonomy:

The species was originally described by Louis Agassiz in 1831 as Lobotes ocellatus, as he mistakenly believed the species was marine; later work assigned the species to the genus Astronotus'.The species also has a number of junior synonyms: Acara compressus, Acara hyposticta, Astronotus ocellatus zebra, and Astronotus orbiculatus.


Description:

A. ocellatus examples have been reported to grow to about 45 cm (18 in) in length and 1.6 kilograms (3.5 lb) in weigh.Although the species is widely regarded as sexually monomorphic males have been suggested to grow more quickly, and in some naturally occurring strains, males are noted to possess dark blotches on the base of the dorsal fin.The species reaches sexual maturity at approximately one year of age, and continues to reproduce for nine to ten years. Frequency and timing of spawning may be related to the occurrence of rain.A. ocellatus fish are biparental substrate spawners, though detailed information regarding their reproduction in the wild is scarce.The closely related Astronotus crassipinnis has been observed, in times of danger, to store food in its mouth, possibly for protection, in a manner reminiscent of mouthbrooding geophaginecichlids. This behaviour, however, has not yet been observed in A. ocellatus. In captivity, pairs are known to select and clean generally flattened horizontal or vertical surfaces on which to lay their 1,000 to 3,000 eggs.

Feeding and selective breeding:
Captive oscars may be fed prepared fish food designed for large carnivorous fish, crayfish, worms, and insects (such as flies, crickets and grasshoppers). Feeding live foods may increase the rate of growth but also may cause endoparasites. Poultry and/or mammalian flesh, including beefheart, should not be fed long term as these fatty foods will contribute to fatty liver disease. Since these fish eat fruit in the wild, items such as melons, oranges, and other fruits can also be used as a type of food. Just about anything that falls into the water would be eaten by oscars. Live feeder fish can be given, but fish such as goldfish and rosy red feeder minnows should not be fed. These contain an enzyme (thiaminase) within their flesh which binds vitamin B₁, leading to deficiency. Most fish eaten by A. ocellatus in the wild are relatively sedentary catfish, including Bunocephalus, Rineloricaria, and Ochmacanthus species.The species uses a suction mechanism to capture prey. and has been reported to exhibit "laying-on-side" death mimicry in a similar fashion to Parachromis friedrichsthalii and Nimbochromis livingstonii. The species also has an absolute requirement for vitamin C, and develops health problems in its absence.A number of ornamental varieties of A. ocellatus have been developed for the aquarium industry. These include forms with greater intensity and quantities of red marbling across the body, albino, leucistic, and xanthistic forms. A. ocellatus with marbled patches of red pigmentation are sold as red tiger oscars, while those strains with mainly red colouration of the flanks are frequently sold under the trade name of red oscars. The patterning of red pigment differs between individuals; in the United Kingdom, one A. ocellatus reportedly had markings that resembled the Arabic word for "Allah".In recent years long-finned varieties have also been developed. The species is also occasionally artificially coloured by a process known as painting.

Snake head fish

Introduction:

The snakeheads are members of the fresh water perciform fish family Channidae, native to africa and asia. These elongated,predatory fish are distinguished by their longdorsal fins, large mouths, and shiny teeth. They breathe air with gills, as well as with suprabrancial organs developing when they grow older, which is a primitive form of alabyrinthy organ. The two extant genera are channa in Asia and parachanna in Africa, consisting of about 35 species.
They are valuable as a food source and have become notorious as an intentionally released invasive species.The various species of snakeheads differ greatly in size. "Dwarf snakeheads", such as channna gachua grow to 25 cm (9.8 in). Most other snakeheads reach between 60 and 90 cm (24 and 35 in). Three species (channa barca , channa marulius and channa micropeltes), can reach a length of more than 1 m (3 ft 3 in).
Snakeheads are thrust-feeders which consume plankton,aquatic insects, and mollusuks when small. As adults, they mostly feed on other fish, such as carp or on frogs. In rare cases, small  mammls such as rats are taken.
Ecological concern:
Snakeheads can become invasive species and cause ecological dammage because they are top-level predators, meaning they have no natural enemies outside of their native environment. Not only can they breathe atmospheric air, but they can also survive on land for up to four days, provided they are wet, and are known to migrate up to 1/4 mile on wet land to other bodies of water by wriggling with their body and fins.national geographic has referred to snakeheads as "Fishzilla" and the National geographic channel reported the "northern snakehead reaches sexual maturity by age two or three. Each spawning-age female can release up to 15,000 eggs at once. Snakeheads can mate as often as five times a year. This means in just two years, a single female can release up to 150,000 eggs.
Since 2002, it has been illegal to possess a live snakehead in many US states, where they are considered a destructive invasive species.

World record:

According to the international game fish association Caleb Newton, a spotsylvania country, Virginia resident, caught a world record 17 pound, 6 ounce northern snakehead at the junction of aqui creek and the  potomac river on June 1, 2013. The previous record, two ounces smaller, had been caught in 2004 in miki,kajawa,japan.


As food:

Snakeheads are considered valuable food fish. Called nga yant in Burmese, it is a prized fish eaten in a variety of ways. In Vietnam, they are called ca loc, ca qua, or ca chuoi; it is prized in clay pot dishes and pickled preparations. Larger species, such as channa striata,channna maculata,  and parachanna obscura, are farmed in aquaculture.In the United States, chefs have suggested controlling the snakehead invasion by serving them in restaurants.In Indonesia, snakehead fish are called ikan gabus, served as the main parts of traditional dishes such as Betawi's pucung gabus, and considered to be a delicacy due to their rarity in wild and aquaculture, as they are harder to raise than other popular freshwater fish such as catfish and carp.

Jelly fish

Introduction:

Jellyfish or jellies are the major non-polyp form of individuals of the phylum Cnidaria. They are typified as free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey.

Jellyfish are found in every ocean, from the surface to the deep sea. A few jellyfish inhabit freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years and possibly 700 million years or more, making them the oldest multi-organ anima

Terminology:

The English popular name jellyfish has been in use since 1796. It has traditionally also been applied to other animals sharing a superficial resemblance, for example ctenophores(members from another phylum of common, gelatinous and generally transparent or translucent, free-swimming planktonic carnivores now known as comb jellies) were included as "jellyfishes". Even some scientists include the phylum ctenophora when they are referring to jellyfish.Other scientists prefer to use the more all-encompassing termgelatinous zooplankton, when referring to these, together with other soft-bodied animals in the water column.

As jellyfish are not vertebrates, let alone true fish, the word jellyfish is considered by some to be a misnomer. Public aquariums may use the terms jellies or sea jellies instead. Indeed, it may be said that the term "jellies" has become more popular than "jellyfish". In scientific literature, "jelly" and "jellyfish" are often used interchangeably.Some sources may use the term "jelly" to refer to organisms in this taxon, as "jellyfish" may be considered inappropriate.

Many textbooks and sources refer to only scyphozoa as "true jellyfish"

A group of jellyfish is sometimes called a bloom or a swarm. "Bloom" is usually used for a large group of jellyfish that gather in a small area, but may also have a time component, referring to seasonal increases, or numbers beyond what was expected. Another collective name for a group of jellyfish is a smack,although this term is not commonly used by scientists who study jellyfish. Jellyfish are "bloomy" by nature of their life cycles, being produced by their benthic polyps usually in the spring when sunshine and plankton increase, so they appear rather suddenly and often in large numbers, even when an ecosystem is in balance. Using "swarm" usually implies some kind of active ability to stay together, which a few species such as Aurelia, the moon jelly, demonstrate.

Medusa jellyfish may be classified as scyphomedusae ("true" jellyfish), stauromedusae(stalked jellyfish), cubomedusae (box jellyfish), or hydromedusae, according to which clade their species belongs.

Toxity:

Jellyfish sting their prey using nematocysts, also called cnidocysts, stinging structures located in specialized cells called cnidocytes, which are characteristic of all Cnidaria. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and injectvenom, yet only some species' venom cause an adverse reaction in humans. When a nematocyst is triggered by contact by predator or prey, pressure builds up rapidly inside it up to 2,000 pounds per square inch (14,000 kPa) until it bursts. A lance inside the nematocyst pierces the victim's skin, and poison flows through into the victim.Touching or being touched by a jellyfish can be very uncomfortable, sometimes requiring medical assistance; sting effects range from no effect to extreme pain to death. Even beached and dying jellyfish can still sting when touched.

Hazards:

Jellyfish adversely affect humanity by interfering with public systems and harming swimmers.The most obvious consequences are human injury or death and reduced coastal tourism. Jellies destroy fish nets, poison or crush captured fish, and consume fish eggs and young fish.

Jellyfish can clog cooling equipment, disabling power plants in several countries. Jellyfish caused a cascading blackout in the Philippines in 1999, as well as damaging the Diablo Canyon Power Plant in California in 2008. Clogging can stop desalination plants, as well as clogging ship engines and infesting fishing nets.

Sea horse (hippocampus)

Introduction:

Seahorse is the title given to 54 species of marine fish in the genus Hippocampus. "Hippocampus" comes from the ancient greek hippos meaning "horse" and kamposmeaning "sea monster"


Habiat:

Seahorses are mainly found in shallow tropical and temperate waters throughout the world, and prefer to live in sheltered areas such as sea grass beds,estuaries, coral reefs, ormangroves. In Pacific waters from North America to South America there are four species. In the Atlantic, the h.erectus ranges from nova scotia to uruguay. h.zosterai, known as the dwarf seahorse, is found in the bahamas.

Colonies have been found in European waters such as the thamus estuary.Three species live in the mediteranan sea h.guttulatus (the long-snouted seahorse),h.hippocampus (the short-snouted seahorse) and h.fuscus (the sea pony). These species form territories; males stay within 1 square meter (11 sq ft) of their habitat while females range about one hundred times that.

Sea horse life cycle:

Reproduction:

e is equipped with a brood pouch on the ventral, or front-facing, side of the tail. When mating, the female seahorse deposits up to 1,500 eggs in the male's pouch. The male carries the eggs for 9 to 45 days until the seahorses emerge fully developed, but very small. Once the seahorses are released into the water, the male's role is done and he offers no further care and often mates again within hours or days during the breeding season.
The male seahors

Birth:

The number of young released by the male seahorse averages 100–1000 for most species, but may be as low as 5 for the smaller species, or as high as 2,500. When the fry are ready to be born, the male expels them with muscular contractions. He typically gives birth at night and is ready for the next batch of eggs by morning when his mate returns. Like almost all other fish species, seahorses do not nurture their young after birth. Infants are susceptible to predators or ocean currents which wash them away from feeding grounds or into temperatures too extreme for their delicate bodies. Less than 0.5% of infants survive to adulthood, explaining why litters are so large. These survival rates are actually fairly high compared to other fish, because of their protected gestation, making the process worth the great cost to the father. The eggs of most other fish are abandoned immediately after fertilization.



Use in china medicine:

Seahorse populations are thought to have been endangered in recent years by overfishing and habitat destruction. The seahorse is used in traditional Chinies herbalogy, and as many as 20 million seahorses may be caught each year and sold for this purpose. Medicinal seahorses are not readily bred in captivity as they are susceptible to disease, and it is believed that they have different medicinal properties from aquarium seahorses. Seahorses are also used as medicines by the Indonesians, the Central Filipinos, and many other ethnic groups.

Import and export of seahorses has been controlled under cites since 15 May 2004. However,indonesia, japan, norway, and South korea have chosen to opt out of the trade rules set by CITES.

The problem may be exacerbated by the growth of pills and capsules as the preferred method of ingesting medication. They are cheaper and more available than traditional, individually tailored prescriptions of raw medicinals, but the contents are harder to track. Seahorses once had to be of a certain size and quality before they were accepted by TCM practitioners and consumers. Declining availability of the preferred large, pale and smooth seahorses has been offset by the shift towards prepackaged medicines, which make it possible for TCM merchants to sell previously unused juvenile, spiny and dark-coloured animals. Today almost a third of the seahorses sold in China are prepackaged, adding to the pressure on the species.

Dried seahorses retails from US$600 – 3000 per kilogram with larger, paler and smoother animals commanding the highest prices. In fact, in terms of value based on weight seahorses retail for more than the price of silver and almost that of gold in Asia. (UNEP,2004)

Electric fish

Introduction:


An electric fish is any fish that can generate electricfields. A fish that can generate electric fields is said to be electrogenic  while a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive.Electric fish species can be found both in the ocean and in freshwater rivers of South America (gymnotymers) and Africa (mormiridae). Many fish such as sharks,rays and catfishes can detect electric fields and are thus electroreceptive, but they are not classified as electric fish because they cannot generate electricity. Most common bony fish (teleosts) including most fish kept in aquaria or caught for food, are neither electrogenic nor electroreceptive.


Strongly and weekly electric fish:

Electric fish produce their electrical fields from a specialized structure called an electric organ. This is made up of modified muscle or nerve cells, which became specialized for producing bioelectric fields stronger than those that normal nerves or muscles produce (Albert and Crampton, 2006). Typically this organ is located in the tail of the electric fish. The electrical output of the organ is called the electric organ discharge (EOD).

Fish with an EOD that is powerful enough to stun prey are called strongly electric fish. The amplitude of the signal can range from 10 to 600 volts with a current of up to 1 ampere. Typical examples are the electric eel (Electrophorus electricus; not a  true eel but a knifefish), the electric cat fishes (family Malapteruridae), and electric rays (order Torpediniformes). Strongly electric marine fish deliver low voltage, high current electric discharges while freshwater fish have high voltage, low current discharges. This is because of the different conductances of salt and fresh water. To maximize the power delivered to the surroundings, the impedances of the electric organ and the water must be matched. In salt water, a small voltage can drive a large current limited by the internal resistance of the electric organ. Hence, the electric organ consists of many electrocytes in parallel. In freshwater, the power is limited by the voltage needed to drive the current through the large resistance of the medium. Hence, these fish have numerous cells in series.

By contrast, weakly electric fish generate a discharge that is typically less than one volt in amplitude. These are too weak to stun prey and instead are used for navigation, object detection (electro location)and communication with other electric fish (electrocommunication). Two of the best-known and most-studied examples are peters elephantanose fish(Gnathonemus petersi) and the black ghost knife fish (Apteronotus albifron)

Pterios also known as lion fish

Introduction:


Pterois, commonly known as lionfish, is a genus of venomous marine fish found mostly in the Indo-Pacific. Pterois is characterized by conspicuous warning coloration with red, white, creamy, or black bands, showy pectoral fins and venomous spiky fin rays.Pterois are classified into a number of different species, but pterious ratiata, pterious volitans and pterious miles are the most commonly studied. Pterois are popular aquarium fish.Pterois in the Atlantic range from 5 centimetres (2.0 in) to 45 centimetres (18 in) in length, weighing from 25 grams (0.88 oz) to 1.3 kilograms (2.9 lb).They are well known for their ornate beauty, venomous spines and unique tentacles. Juvenile lionfish have a unique tentacle located above their eye sockets that varies in phenotype between species. It is suggested that the evolution of this tentacle serves to continually attract new prey; studies also suggest that it plays a role in sexual selection.


Behaviour:

Pterois can live from five to fifteen years and have complex courtship and mating behaviors. Females release two mucus-filled egg clusters frequently, which can contain as many as fifteen thousand eggs. Studies on Pterois reproductive habits have increased significantly in the past decade. All the species are aposematic they have conspicuous coloration with boldly contrasting stripes and wide fans of projecting spines, advertising their ability to defend themselves.


PREY AND PREDATOR:
According to a study that involved the dissection of over 1,400 lionfish stomachs from Bahamian to North Carolinian waters, Pterois prey mostly on small fish, invertibrates and mollusksin large amounts, with some specimens’ stomachs containing up to six different species of prey. The amount of prey in lionfish stomachs over the course of the day suggest that lionfish feed most actively from 7:00–11:00 am, with decreased feeding throughout the afternoon. Lionfish are skilled hunters, using specialized bilateral swim bladder muscles to provide exquisite control of location in the water column, allowing the fish to alter its center of gravity to better attack prey. The lionfish then spreads its large pectoral fins and swallows its prey in a single motion.Researchers have also noted that lionfish blow jets of water while approaching prey, apparently in order to disorient them.Aside from instances of larger lionfish individuals engaging in canniballisum on smaller individuals, adult lionfish have few identified natura lpredators. This is likely due to the effectiveness of their venomous spines. Moray eels (family muraenidae bluespotted cornetfish  and large groupers like the tiger grouper and Nassau grouper , have been observed preying on lionfish.It remains unknown, however, how commonly these predators prey on lionfish.Sharks are also believed to be capable of preying on lionfish with no ill-effects from its spines.Park officials of the roatan marine park in Honduras have attempted to train sharks to feed on lionfish as of 2011 in an attempt to control the invasive populations in the Caribbean. Predators of larvae and juvenile lionfish remain unknown, but may prove to be the primary limiting factor of lionfish populations in their native range.

Hazard to human:

Lionfish are known for their venomous fin rays, a feature that is uncommon among marine fish in the East Coast coral reefs. The potency of their venommakes them excellent predators and poisonous to fishermen and divers. pterious venom produced negative inotropic and chronotropic effects when tested in both frog and clam hearts and has a depressing effect on rabbit blood pressure.These results are thought to be due to nitric oxide release. In humans, Pterois venom can cause systemic effects such as extreme pain, nausea, vomting, fever, breathing difficulties, convulsionus, diizziness, redness on the affected area, headache, numbness,presthesia (pins and needles), heart burn, diarrhea and sweating. Rarely, such stings can cause temporary paralysis of the limbs,heart failure and even death. Fatalities are common in very young children, the elderly, those with a weak immune system or those who are allergic to their venom. Their venom is rarely fatal to healthy humans, but some species have enough venom to produce extreme discomfort for over a period of several days. However, Pterois venom is a danger to allergic victims as they may experience anaphylixis, a serious and often life threatening condition that requires immediate emergency medical treatment. Severe allergic reactions to Pteroisvenom include chest pain, severe breathing difficulties, a drop in blood preassure, swelling of the tongue, sweating, runny nose, or slurred speech. Such reactions can be fatal if not treated.

Lionfish are edible if prepared correctly.

Crab

Introduction:

Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" οura = tail usually entirely hidden under the yhoraxThey live in all the world's oceans, in fresh water, and on land, are generally covered with a thick exoskeleton and have a single pair of claws. Many other animals with similar names such as hermit crabs king crabs, porcelin crab,horse shoe cdrabs and crab lice are not true crabs.

Evolution:

Crabs are generally covered with a thickexoskeleton  composed primarily of calcium carbonate and armed with a single pair ofchelae (claws). Crabs are found in all of the world's oceans, while many crabs live in fresh water and on land, particularly in tropical regions. Crabs vary in size from the pea crab a few millimetres wide, to the japanes apider crab with a leg span of up to 4 metres (13 ft).

The underside of a male (top) and a female (bottom) individual of pachygrapsus marmoratus, showing the difference in shape of the abdomen.


Use in food:

Crabs are prepared and eaten as a dish in several different ways all over the world. Some species are eaten whole, including the shell, such as soft shell crab with other species just the claws and/or legs are eaten. The latter is particularly common for larger crabs, such as the snow crab. Mostly in east asian cultures, the roe of the female crab is also eaten, which usually appears orange or yellow in colour in fertile crabs.

The biggest importers, and therefore countries where eating crab is immensely popular, are Japan, France, Spain, Hong Kong, the US, Canada and Portugal.

Cat fish

Introduction:
Catfishes (orderSiluriformes) are a diverse group of ray-finned catfish. Named for their prominent barbels, which resemble a cat whiskers, catfish range in size and behavior from the heaviest and longest, the mekong giant catfish from Southeast Asia and the second longest, the wels catfishh of Eurasia, to detritvores (species that eat dead material on the bottom), and even to a tiny parasitic species commonly called the candiru,Vandellia cirrhosa. There are armour-plated types and also naked types, neither having scales. Despite their name, not all catfish have prominent barbels; members of the Siluriformes order are defined by features of the skull and swimbladders. Catfish are of considerable commercial importance; many of the larger species are farmed or fished for food. Many of the smaller species, particularly the genus corydoras, are important in the aquariumhobby.

Habitat:

Extant catfish species live inland or in coastal waters of every continent except antarctica. Catfish have inhabited all continents at one time or another Catfish are most diverse in tropical South America, North America, Africa, and Asia More than half of all catfish species live in the Americas. They are the only ostariophysians  that have entered fresh water habitats in madagascar, Australia, and new guinea

They are found in freshwater environments, though most inhabit shallow, running waterRepresentatives of at least eight families are hypogen (live underground) with three families that are also troglobitic (inhabiting caves).One such species is phreatibuos cistermarum known to live underground in phreatic habitats. Numerous species from the families ariidae and plotosidae and a few species from among the asprinadie and bagridae are found in salt water.

In the United States, catfish species may be known by a variety of slang names, such as "mud cat", "polliwogs", or "chuckleheads"

Sound production and intrepption:

Catfish can produce different types of sounds and also have well-developed auditory reception used to discriminate between sounds with different pitches and velocities. They are also able to determine the distance of the sound's origin and in what direction it originated.This is a very important fish communication mechanism, especially during agonistic and distress behavior. Catfish are able to produce a variety of sounds for communication that can be classified into two groups: drumming sounds and stridulation sounds. The variability in catfish sound signals differs due to a few factors: the mechanism by which the sound is produced, the function of the resulting sound, and physiological differences such as size, sex, and age.In order to create a drumming sound, catfish utilize an indirect vibration mechanism using a swimbladder. In these fishes, sonic muscles insert on the ramus Mulleri, also known as the elastic spring. The sonic muscles pull the elastic spring forward and extend the swimbladder. When the muscles relax, the tension in the spring quickly returns the swimbladder to its original position, which produces the sound.Catfish also have a sound generating mechanism in their pectoral fins. Many species in the catfish family possess an enhanced first pectoral fin ray, called the spine, which can be moved by large abductor and adductor muscles. The base of the catfishes’ spine has a sequence of ridges, and the spine normally slides within a groove on the fish’s pelvic girdle during routine movement; but, pressing the ridges on the spine against the pelvic girdle groove creates a series of short pulses. The movement is analogous to a finger moving down the teeth of a comb, and consequently a series of sharp taps is produced.

Dangerous to human:

Many catfish species have “stings” (actually non-venomous in most cases) embedded behind their fins; thus precautions must be taken when handling them.While the vast majority of catfish are harmless to humans, a few species are known to present some risk. Perhaps the most notorious of these is the candiru, due to the way it is reputed to parasitize the urethra, though there is only one documented case of a candiru attack on a man.