Category Archives: Fish

Atlantic Salmon (Salmo salar)

Female-Atlantic-salmon

  • Name: Atlantic salmon
  • Latin: Salmo salar
  • Classification: Ray-finned fish
  • Origin: North Atlantic ocean
  • Lifespan: 4-6 years
  • AKA: Black salmon

Taxonomy

  • Kingdom: Animalia (Animals)
  • Phylum: Chordata (Vertebrates)
  • Class: Actinopterygii (Ray-finned fish)
  • Order: Salmoniformes (Salmonids)
  • Family: Salmonidae (Salmonids)
  • Genus: Salmo (Salmon)
  • Species: Salmo salar (Atlantic salmon)

Appearance

  • Length: 28-30in (70-75cm)
  • Weight: 8-12lbs (3.5-5.5kg)

diagram

The Atlantic salmon is a large fish with a small head and eyes and a blunt nose. Its mouth reaches back below the eye and is filled with short, conical teeth. Its caudal fins are slightly forked and has an adipose fin on its back, present in all species of trout. It is distinguished from its Pacific cousins by its anal fin, which has a maximum of 12 rays. It also has a narrow ‘wrist’ on the tail, which differentiates it from sea trout.

The Atlantic salmon has large scales and during feeding periods, the flanks are silver and back dark green-blue and black spots are flecked above the lateral line. During spawning, adults become darker in colour, with their flanks becoming red or bronze with reddish spots. Females can appear to be almost black. During spawning, males develop a hooked jaw (called a ‘kype’) used for fighting other males for fertilization rights.

Atlantic-salmon-male
Male showing the ‘kype’ jaw shape.

Relatives

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  • Chinook salmon (Oncorhynchus tshawytscha) -NOT EVALUATED-
  • Sockeye salmon (Oncorhynchus nerka) -LEAST CONCERN-
  • Pink salmon (Oncorhynchus gorbuscha) -LEAST CONCERN-
  • Coho salmon (Oncorhynchus kisutch) -NOT EVALUATED-
  • Chum salmon (Oncorhynchus keta) -NOT EVALUATED-

Habitat & Distribution

Atlantic salmon alternate between freshwater and ocean habitats. They are born in coastal rivers in northeastern North America, Iceland and Europe where they spend the first 2-3 years of their life. Here, they prefer to live near gravel and boulders where the water is clean and well oxygenated or near natural grassy banks and overhanging deciduous trees. Insects (which young salmon feed on) will occasionally fall into the rivers and estuaries and the trees provide shade and some cover from predators. While in these rivers, salmon will undergo a physiological change called ‘smoltification’ which prepares them for life in the ocean. Their bodies become more streamlined and develop a silver colouring. It is also thought that they imprint on the rivers they will return to later in life to spawn.

Atlantic salmon will then migrate through the North Atlantic Ocean and share feeding grounds off the coast of Greenland to feed, as the ocean has a much better supply of nutritious food than their river birthing grounds. They will stay in the ocean for a further 2-3 years before return to their rivers to spawn and reproduce.

Gadus_morhua-Atlantic_cod
Map of distribution of the Atlantic salmon

Diet

Soon after the yolk sac is absorbed, young salmon begin to hunt and feed off very small organisms and occasionally, salmon eggs. The most common include caddisflies, blackflies, mayflies, stoneflies and plankton and will hunt in both the substrate and the current.

After the smoltification process, the salmon grow larger, move downstream into the ocean and feed on much larger prey, including Arctic squid, sand eels, amphipods, Arctic shrimp and sometimes herring.

Reproduction

After spending 2-3 years in the ocean, Atlantic salmon will migrate as much as thousands of miles back to their natal coastal rivers to spawn during the summer and autumn. They will swim against river currents and have to leap over several waterfalls, only the fittest will reach the spawning grounds and reproduce.  They stop feeding as they enter freshwater and rely on their fat reserves for energy. Their stomach disintegrates internally to make room for eggs and sperm.

Males will arrive first and stake out territories. During this time, the mouths of the males change and become more hooked and pincer-like, called a ‘kype’. This displays the male’s dominant characteristics to females and is used in fighting other males for females. Territories with shallow, gravel beds are preferred with the right amount of river flow. Enough to oxygenate the eggs but not so strong that they wash eggs away.

When females arrive, they initiate spawning by digging a shallow nest in the gravel, known as a ‘redd’ and is created by the female turning into one side and fanning her tail. The female then signals to a male that she is ready to lay by touching her anal fin to the gravel. The male joins the female, and side by side, they release their gametes (eggs and sperm) above the redd.

sa0933
Eggs and milt

The female released 2,000-10,000 small, orange eggs about the size of a small pea. The male releases a while milt, which contains millions of sperm over the eggs, and fertilization occurs externally. The pair then moves upstream and repeat the process until they are out of their energy or gametes. The males may spawn with several females, however, females will typically only spawn with a single male. The entire reproduction process takes a day or two once the pair reach the spawning grounds.

Fertilized eggs hatch within 3-4 months and emerge in the form on an alevin, where they still have the yolk sac attached to their bodies near the throat, which lasts about a month before the young begin to hunt for themselves. After 5-10 weeks they are known as a ‘fry’ and after several months, when they have developed their ‘tiger-like’ markings, they are called a ‘parr’.

433ae373-2679-4449-9dc4-343453f4e3c3_04_Salmon alevin (photo by Yoeri van Es)_30418c95_490x330
Salmon alevin

Adaptations

  • The lateral line of a fish, runs along the length of its body and acts as a ‘sixth sense’. It allows the fish to detect which way is up in water. Atlantic salmon also use this line to detect the flow of the current around them, aiding them in their migration to their natal rivers.
  • Atlantic salmon have four sets of gills with specialized cells that allow them to migrate between salt and fresh water, and are efficient in the dissolving of oxygen. When in saltwater, salt is taken from the water flowing over the gills and expelled via a gland. This process is called ‘osmoregulation’.

MAR_gill_disease_check_th

  • The sense of smell of the Atlantic salmon is approximately 1,000 times greater than that of a dog. It is thought this superior sense of smell is used to aid the fish with navigation during their migration. In an experiment carried out in Canada. A salmon was able to detect a single drop of a substance (prostaglandin-A) in the equivalent of eight Olympic sized swimming pools of water.

Threats

Atlantic salmon survival can be affected immensely by river pollution. They require clean and well oxygenated water in order to spawn and for smolts to grow. Pollution can be caused by chemicals, oil and rubbish as well as acid rain and agricultural run-off. Large numbers of cattle walking through the river can also disturb salmon by kicking up mud, causing eggs to become destroyed or by making it near impossible for females to create their redds. Erosion can also cause river banks to collapse into the water which can be caused by overgrazing and deforestation. Run-off can also cause an increase in nutrients which results in ‘algal blooms’. The increased vegetation eventually die off and cause an increase in bacteria, which uses up the valuable oxygen the salmon need. Dams and other water obstructions can also prevent salmon from migrating back to their spawning grounds, resulting in a decrease of young.

Atlantic salmon are also affected by alien species, most notably the American signal crayfish (Pacifastacus leniusculus) which were introduced to Scotland in the mid-1970’s for aquaculture. This crayfish burrows into riverbanks, which weakens them and makes them more likely to collapse. It also feeds on insects, fish eggs and fry (including salmon).

American-Signal-Cr_2504959b
American signal crayfish (Pacifastacus leniusculus)

Salmon can also be affected by disease such as the ulcerative dermal necrosis (UDN) which was caught by most salmon in Scotland in the 70’s and nearly wiped out the entire population. Parasites such as Gyrodactylus salaris and Henneguya salminicola can attach to salmon using their hooked feet and can affect the gills, fins and skin and occurs in over 20 Norwegian rivers. Climate change can also affect salmon survival by increasing water temperature. Smolts struggle to survive in higher temperatures and can also affect growth rates and prey availability.

Henneguya_salminicola_in_flesh_of_coho_salmon,_BC,_Canada
Salmon meat affected by Henneguya salminicola

Atlantic salmon are commonly farmed in many rivers throughout Norway and the west coasts of Ireland and Scotland. The high concentrations of fish can cause sea lice to multiply drastically which can effect wild fish as well as those in fish farms. Escapees from these farms can also interbreed with wild fish which reduces the fitness of future generations. These farms can also increase water pollution due to a build-up of uneaten food, feces and medication. This can also lead to a rapid spread of infection among all fish.

Conservation

IUCN Status: Least Concern

logo_nasco_140x110

There are several non-profit organizations which work to actively protect or provide funding for the protection and conservation of the Atlantic salmon. One of which is the North Atlantic Salmon Conservation Organization (NASCO), which soon after it was established, created a fishing free sanctuary by prohibiting fishing in most parts of the North Atlantic 12 nautical miles from the coast. They have also developed Precautionary Approach agreements in relation to:

  • “Management of fisheries,
  • Habitat protection and restoration,
  • Impacts of aquaculture, introductions and transfers of transgenics,
  • Stock rebuilding programs,
  • Use of socio economic factors in management decisions.”

ASCF1_61973_The_Atlantic_Salmon_Cons_Foundation2The Atlantic Salmon Conservation Foundation also works to “promote enhances community partnerships of salmon and its habitat in Atlantic Canada and Quebec”. It operates as a source of funding for the conservation of the Atlantic salmon and its habitat and to improve public awareness, education and research of the animal and its conservation efforts.

Atlantic salmon can be actively supported by way of ‘supportive breeding’, which includes capturing wild individuals, breeding them in captivity and then release. Fish ladders can also be installed in order to aid the migration of the salmon around man-made obstacles. The salmon leap over each step in order move over the obstacle. Adding limestone to rivers can also neutralized acidity levels of the water. This process is known as ‘liming’. River banks can also be stabilized against erosion by reforesting the area (without conifers, as the needles are acidic and can cause the acidity level of the water to rise by dropping into the river).

fish-ladder
Fish ladder

Fun Facts

  • Male: Cock
  • Female: Hen
  • Young: Alevin / fry / parr
  • Group: run / shoal / bind / draught
  • When Atlantic salmon return to their natal rivers, they lose all their teeth and grow new ones.
  • Atlantic salmon will swim up to 2,500 miles to reach their feeding grounds.
  • Atlantic salmon are one of only 87 species of fish to migrate between salt and freshwater.
  • Mature females can carry up to 22% of their body weight in eggs.
  • A female can lay up to 1,600 eggs per kilogram of her body weight.

Cherry Maureen Iris Franklin, Bsc (Hons)

1 May 2016

References

Animal Diversity Web (2016) Salmo salar (Atlantic Salmon) [Online] Available at: http://animaldiversity.org/accounts/Salmo_salar/ [Accessed: 1 May 2016]

Arkive (2016) Atlantic Salmon (Salmo salar) [Online] Available at: http://www.arkive.org/atlantic-salmon/salmo-salar/ [Accessed: 27 April 2016]

Atlantic Salmon Conservation Foundation (2016) About Us [Online] Available at: http://salmonconservation.ca/en/about-us/ [Accessed: 1 May 2016]

Atlantic Salmon Federation (2012) Migration [Online] Available at: http://www.asf.ca/migration.html [Accessed: 1 May 2016]

Atlantic Salmon Trust (2016) Atlantic Salmon Habitats [pdf] Available at: http://www.atlanticsalmontrust.org/learning-zone-assets/atlantic_salmon_habitats.pdf [Accessed: 27 April 2016]

Atlantic Salmon Trust (2016) What is Osmoregulation? [Online] Available at: http://www.atlanticsalmontrust.org/salmon-and-sea-trout-facts/what-is-osmoregulation.html [Accessed: 1 May 2016]

Atlantic Salmon Trust (2016) Atlantic Salmon Threats [pdf] Available at: http://www.atlanticsalmontrust.org/learning-zone-assets/atlantic_salmon_threats.pdf [Accessed: 1 May 2016]

BBC Wildlife (2014) Atlantic Salmon [Online] Available at: http://www.bbc.co.uk/nature/life/Atlantic_salmon [Accessed: 27 April 2016]

Bioweb (2016) Habitat & Adaptations [Online] Available at: http://bioweb.uwlax.edu/bio203/s2009/webb_laur/Habitat.htm [Accessed: 29 April 2016]

Defenders (2016) Basic Facts about Salmon [Online] Available at: http://www.defenders.org/salmon/basic-facts [Accessed: 29 April 2016]

EDC (2016) Atlantic Salmon (Salmo salar) [Online] Available at: http://www.edc.uri.edu/restoration/html/gallery/fish/salmon.htm [Accessed: 27 April 2016]

Fisheries Research Services (2016) Signal Crayfish – An Unwelcome Addition to Scottish Streams [pdf] Available at: http://www.gov.scot/Uploads/Documents/FW-SignalCrayfish.pdf [Accessed: 1 May 2016]

IUCN (2016) Salmo salar [Online] Available at: http://www.iucnredlist.org/details/19855/0 [Accessed: 1 May 2016]

Marine Science (2006) Salmon Reproduction [Online] Available at: http://www.marinebio.net/marinescience/05nekton/sarepro.htm [Accessed: 29 April 2016]

NatureGate (2016) Atlantic Salmon [Online] Available at: http://www.luontoportti.com/suomi/en/kalat/atlantic-salmon [Accessed: 27 April 2016]

NOAA Fisheries (2016) Atlantic Salmon (Salmo salar) [Online] Available at: http://www.fisheries.noaa.gov/pr/species/fish/atlantic-salmon.html [Accessed: 27 April 2016]

NASCO (2015) About NASCO [Online] Available at: http://www.nasco.int/about.html [Accessed: 1 May 2016]

NASCO (2016) Protection, Restoration and Enhancement of Salmon Habitat – Focus Area Report [pdf] Available at: http://www.nasco.int/pdf/far_habitat/HabitatFAR_Norway.pdf [Accessed: 1 May 2016]

Western Morning News (2015) Deadly Skin Disease Hits Salmon Stocks in Devon River [Online] Available at: http://www.westernmorningnews.co.uk/Officials-fishing-ban-disease-hits-salmon-Devon/story-26892382-detail/story.html [Accessed: 1 May 2016]

Wikipedia (2016) Atlantic Salmon [Online] Available at: https://en.wikipedia.org/wiki/Atlantic_salmon [Accessed: 27 April 2016]

 

 

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Basking Shark (Cetorhinus maximus)

Basking-shark-feeding-mouth-detail

  • Name: Basking shark
  • Latin: Cetorhinus maximus
  • Classification: Cartilaginous fish
  • Origin: Worldwide
  • Lifespan: 20-100 years

Taxonomy

Kingdom: Animalia (Animals)
Phylum: Chordata (Vertebrates)
Class: Chondrichthyes (Cartilaginous fishes)
Order: Lamniformes (Mackerel sharks)
Family: Cetorhinidae (Basking Shark)
Genus: Cetorhinus (Basking Shark)
Species: Certorhinus Maximus (Basking Shark)

Apperance

Length: 10m
Weight: 7 tons

Basking sharks are greyish brown in colour with their bellies being slightly paler. They have a large snout which ends in a roundish point. The mouth opens incredibly wide so it stretches right around its head, giving the impression that is it ‘smiling’, lining its enormous mouth are 100 tiny, rounded teeth. A series of long gill slits surround its blunt head. It has a large, triangular dorsal fin with a smaller second dorsal fin and anal fins. The basking shark has a huge liver (making up 25% of its total body weight) which provides it with natural buoyancy.

Relatives

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  • Spiny dogfish (Squalus acanthias) -VULNERABLE-
  • Prickly shark (Echinorhinus cookei) -NEAR THREATENED-
  • Angular roughshark (Oxynotus centrina) -VULNERABLE-
  • Sand devil (Squatina durmeril) -DATA DEFICIENT-

Habitat & Distribution

The basking shark is highly migrational and is known to keep emerging and disappearing in different areas around the globe. They are mostly found of the coast of Northern Ireland and the UK. They seem to prefer temperate oceans and can also be found in the Western Mediterranean sea and the western Atlantic Ocean. They are never found in the tropics. In spring and winter, they have been spotted off the coast of California; however, they are usually found wherever plankton levels are high. In winter, they seem to migrate from shallow to deeper waters; however, their exact pattern of migratory behaviour is yet to be understood clearly.

Map of distribution of the basking shark
Map of distribution of the basking shark

Diet

Basking sharks are found feeding near the surface of the water. Their mouth can open 1.2meters wide and can swim with its mouth open. This allows the water to pass through its gills, prey gets entangled in its gill rakers and is then digested by the shark by closing the movement of its mouth. This feeding behaviour makes them different from the two other filter feeding species. The basking shark eats barnacles, fish eggs, tiny copepods, deep water oceanic shrimp and decapods larvae, however, its diet is made up mostly of plankton.

Behaviour

Basking sharks are slow swimmers who cruise around 2.5-4 mph. They swim by moving their bodies from side to side, not just their tails like other breeds of shark. They also exhibit breeching behaviour, which consists of a sudden explosion of the shark from the water into the air, rolling in mid-air and then crashing back into the sea. The shark will repeat this display 3-4 times in a row. The reason of this behaviour is unknown and also proves to be dangerous to boats, which can cause them to capsize.

Reproduction

There is limited information about the reproduction cycle of the basking shark, but it has been discovered that they are viviparous and the pups demonstrate oophagy (developing pups will feed on unfertilized eggs). Both sexes take up to 18 years to mature. The gestation period was originally estimated to be at around 3.5 year, but this figure has recently been revised to 14 months. The pups are 1.5-2 meters at birth.

Adaptations

  1. The Basking shark has a large mouth which it holds open while swimming. This enables it to filter food from as much as 2,000 tons of water per hour.
  2. The Basking sharks large size means that is has very little natural predators, aside from humans. However, killer whales have been spotted feeding of this animal’s carcass.
  3. Basking sharks have gill rakers along their gills which trap plankton and other invertebrates while it is filtering food.
  4. Basking sharks are named from their behaviour of basking in shallow water. They do this to warm themselves, feed and mate.

Threats

The biggest threat to basking sharks is hunting for its liver oil, meat, cartilage and fins. The oil is rich in vitamin A and is used as a lubricant for machinery, to tan leather and as lamp oil. The livers are sold as an aphrodisiac and is used as an ingredient in health food products and in cosmetics.

Hunting of these sharks are especially at large in Asia, where there fins are used in the infamous shark fin soup. They are captured and killed in Asian shark fisheries where they are either caught in nets or harpooned.

In the wild, they can be struck by boats and jet skis and can be intimidated by tourists hoping to get close to these creatures.

Conservation

IUCN Status: Vulnerable

The Wildlife Trust has currently set up a Basking Shark Project, which aims to shut down UK shark fisheries and educate the public about this species and the dangers they face in our waters. This will hopefully reduce the number of basking sharks killed in boat accidents.

Since this project has come into play, many UK shark fisheries have shut down although many of these animals are illegally hunted, killed and traded to Asia, who pay a lot of money to use their find in their traditional dish, shark fin soup.

Fun Facts

Male: Bull
Female: Cow
Young: Calf
Group: Gam, Grind, School, Herd, Pod, College, Shiver

-Sharks have existed for around 400 million years, long before the dinosaurs.
-A shark may use around 20,000 teeth during its life.

Common Lionfish (Pterois volitans)

Common lionfish

(http://www.arkive.org/common-lionfish/pterois-volitans/)

  • Name: Common lionfish
  • Latin: Pterois volitans
  • Classification: Fish
  • Origin: Australia
  • Lifespan: 15 years

Taxonomy

  • Kingdom: Animalia (animals)
  • Phylum: Chordata (vertebrates)
  • Class: Actinopterygii (fish)
  • Order: Scorpaeniformes (ray-finned fish)
  • Family: Scorpaenidae (marine fish)
  • Genus: Pterois (found in the Indo-Pacific)
  • Species: Pterois volitans (common lionfish)

Apperance

  • Length: 11.8-15in (30-38cm)
  • Weight: Up to 2.6lbs (1.2kg)

The lionfish is clad in a series of zebra-like stripes, the colour of which vary among the different types of lionfish. It has up to 18 long, needle-like pectoral fins which it uses to sting and poison its prey.

Relatives

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  • Anglerfish (Lophius piscatorius) -NOT EVALUATED-
  • Atlantic salmon (Salmo salar) -LEAST CONCERN-
  • Weedy seadragon (Phycodurus eques) -NEAR THREATENED-
  • Red-bellied piranha (Pygocentrus nattereri) -NOT EVALUATED-

Habitat & Distribution

Lionfish tend to live in coral reefs in shallow waters and hover near caves or crevices. They live in the warm waters of the Indo-Pacific oceanic region, ranging from Western Australia and Malaysia to the French Polynesia and the Pitcairn Islands. They can also be found in places such as South Japan, South Korea and the southern part of coastal Australia. Also, due to recent introduction, they can be found in the Eastern Atlantic Ocean, Azores, the Mediterranean Sea, the Caribbean Sea and the Red Sea.

They can also be found in the waters surrounding Florida. This is widely believed to be because an aquarium was hit by Hurricane Andrew. DNA from captured lionfish from the area have proven that they nearly all originated from the same six or seven fish.

(http://www.speciesinspace.com/species-in-space/category/fish%20fridays)

Diet

The diet of a lionfish consists mainly of fish and shrimp and it relies on its lightning-fast reflexes and camouflage to help capture it. When hunting, the lionfish will use its large fins to corner its prey and then uses its quick reflexes to swallow it whole. It hunts mainly from late afternoon till dawn. It only uses its poisonous spines for protection not to capture prey. The poison of a lionfish is painful to humans but not lethal.

Behaviour

Lionfish are not aggressive towards humans and will keep their distance when given the opportunity to do so. Their poisonous spines are used only for protection instead of hunting. It will face an attacker in an upside down position which exposes its poisonous spines.

When hunting for prey it will corner it using its large fins, then swallow it whole using its lightning-fast reflexes.

Reproduction

When courting, a male will form a group of other lionfish of about 3-8, including a number of females. The lead male of this group will become extremely aggressive and chase off intruders while showing off its poisonous spines. When ready for mating the male becomes darker in colour and its stripes are much less visible. The female will become much paler and many areas of the body will become a silvery white. A female lionfish can lay from 4,000 to 30,000 eggs at one time.

Juvenile common lionfish in diver's hand

(http://www.arkive.org/common-lionfish/pterois-volitans/image-G85262.html)

Adaptations

  • The colourful markings and the long fins on a lionfish help it to blend into its coral background.
  • The lionfish can deliver a very powerful venom from its fins that can cause nausea and breathing difficulties in humans, however, it is rarely fatal.
  • The lionfish has a swim bladder which helps it to maintain its buoyancy whilst in the water.
  • The lionfish is a ‘wait-and-strike’ hunter. It hides, camouflaged, among coral and waits for a fish to swim past, then lunges out and eats it. The lionfish is a nocturnal hunter, eating only at night.

Threats

The only real threat to the population of the lionfish is the fact that they are slow breeders. It doesn’t have any real enemies in the wild although grouper and other fish have been found with lionfish remains in their stomachs.

Conservation

  • IUCN Status: Least Concern

Lionfish are not listed as being threatened or endangered, as they can currently be found in most warm water areas of the world. Therefore no conservation is needed for this animal.

Fun Facts

  • Male: Male
  • Female: Female
  • Young: Fry
  • Group: Shoal, School
  • A lionfish can have up to 18 pectoral fins,
  • The lionfish is also known as a turkey fish, a dragon fish and a scorpion fish,
  • They are very popular as pets.