Salmon is the common name for several species of fish of the family Salmonidae. Several other fish in the family are called trout. Salmon live in both the Atlantic and Pacific Oceans, as well as the Great Lakes and other land locked lakes.

Typically, salmon are salt water fish. anadromous: they are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. However, there are rare species that can only survive in fresh water habitats. This is most likely due to the domestication of these certain species of Salmon. Folklore has it that the fish return to the exact spot where they were born to spawn.

Environmental pressures

Many wild Salmon stocks have seen a marked decline in recent decades, especially north Atlantic populations which spawn in western European and eastern Canadian waters, and wild salmon of the Snake and Columbia River systems in the Northwest USA. The causes of these declines likely include a number of factors, among them:

• Disease transfer from open net cage salmon farming, especially sea lice. The European Commission (2002) concluded “The reduction of wild salmonid abundance is also linked to other factors but there is more and more scientific evidence establishing a direct link between the number of lice-infested wild fish and the presence of cages in the same estuary.”^[9] It is reported that wild salmon on the west coast of Canada are being driven to extinction by sea lice from nearby salmon farms.^[10]
• For Atlantic salmon smolts, it takes as few as eight sea lice to kill the fish. On the Pacific Coast where the smolt are much smaller, only one or two are needed. In the Atlantic, sea lice have been a proven factor in both Norwegian and Scottish salmon. In the Western Atlantic there has been little research at sea, but sea lice numbers in the period post-2000 do not appear to be a significant factor in the critical decline of endangered inner Bay of Fundy salmon. The situation may have been different in the 1980s and 1990s, but we are unlikely ever to know the true facts on that.
• Overfishing in general but especially commercial netting in the Faroes and Greenland.
• Ocean and river warming which can delay spawning and accelerate transition to smolting.
• Ulcerative dermal necrosis (UDN) infections of the 1970s and 1980s which severely affected adult salmon in freshwater rivers.
• Loss of suitable freshwater habitat, especially degradation of stream pools and reduction of suitable material for the excavation of redds. Historically stream pools were, to a large extent, created by beavers. With the extirpation of the beaver, the nurturing function of these ponds was lost.
• Reduction of the retention of the nutrients brought by the returning adult salmon in stream pools. Without stream pools, dead adult salmon tend to be washed straight back down the streams and rivers.
• The construction of dams, weirs, barriers and other “flood prevention” measures, which bring severe adverse impacts to river habitat and on the accessibility of those habitats to salmon. This is particularly true in the northwest USA, where large numbers of dams have been built in many river systems, including over 400 in the Columbia River Basin.
• Loss of invertebrate diversity and population density in rivers because of modern farming methods and various sources of pollution, thus reducing food availability.
• Reduction in freshwater base flow in rivers and disruption of seasonal flows, because of diversions and extractions, hydroelectric power generation, irrigation schemes, and slackwater reservoirs, which inhibit normal migratory processes and increase predation for salmon.

There are efforts to relieve this situation. As such, several governments and NGOs are sharing in research and habitat restoration efforts.

• In the western Atlantic, the Atlantic Salmon Federation has developed a major sonic tracking technology program to understand the high at-sea mortality since the early 1990s. Ocean arrays are deployed across the Baies des Chaleurs and between Newfoundland and Labrador at the Strait of Belle Isle. Salmon have now been tracked half way from rivers like the Restigouche to Greenland feeding grounds. Now the first line of the Ocean Tracking Network initiative is installed by DFO and Dalhousie University of Halifax from Halifax to the edge of the continental shelf. First results include Atlantic salmon travelling from the Penobscot River in Maine, the “anchor river” for US Atlantic salmon populations.

Results overall are showing that estuary problems exist for some rivers, but issues involving feeding grounds at sea are impacting populations as well. In 2008 returns were markedly improved for Atlantic salmon on both sides of the Atlantic Ocean, but no one knows if this is a temporary improvement or sign of a trend.

]]> http://hbkman.wordpress.com/2008/10/23/salmon/feed/ 0 hbkman Illustration of a male Coho Salmon Salmon die shortly after spawning. This one was photographed at a spawning site along Eagle Creek in Oregon. http://hbkman.wordpress.com/2008/10/23/arowana-or-arwana/ http://hbkman.wordpress.com/2008/10/23/arowana-or-arwana/#comments Thu, 23 Oct 2008 13:22:23 +0000 hbkman http://hbkman.wordpress.com/?p=23 ]]> Arowana

Classification and zoogeography

Osteoglossids are basal (primitive) fish from the lower Tertiary and are placed in the actinopterygiid order Osteoglossiformes. There are ten described living species: three from South America, one from Africa, four from Asia, and the remaining two from Australia.

Osteoglossidae is the only exclusively freshwater fish family found on both sides of the Wallace Line. This may be explained by the fact that Asian arowanas (S. formosus) diverged from the Australian Scleropages, S. jardinii and S. leichardti, about 140 million years ago, making it likely that Asian arowanas were carried to Asia on the Indian subcontinent.

Behavior

Osteoglossids are carnivorous, often being specialized surface feeders. They are excellent jumpers; it has been reported that Osteoglossum species have been seen leaping more than 6 feet (almost 2 metres) from the water surface to pick off insects and birds from overhanging branches in South America, hence the nickname “water monkeys”. Arowanas have been rumored to capture prey as large as low flying bats and small birds. All species are large, and the arapaima is a contender for the world’s largest freshwater fish title. Arowana typically grow around 3 to 4 feet, but this is only accountable in captivity.

Several species of osteoglossid exhibit extensive parental care. They build nests and protect the young after they hatch. Some species are mouth brooders, the parents holding sometimes hundreds of eggs in their mouths. The young may make several tentative trips outside the parent’s mouth to investigate the surroundings before leaving permanently.
]]> http://hbkman.wordpress.com/2008/10/23/arowana-or-arwana/feed/ 0 hbkman Silver arowana, Osteoglossum bicirrhosum http://hbkman.wordpress.com/2008/10/23/piranha/ http://hbkman.wordpress.com/2008/10/23/piranha/#comments Thu, 23 Oct 2008 13:20:38 +0000 hbkman http://hbkman.wordpress.com/?p=21 ]]> Piranha Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Characiformes
Family:	SerrasalmidaeA piranha or piraña (pronounced /pɨˈrɑːnjə/, /pɨˈrænjə/, /pɨˈrɑːnə/, or /pɨˈrænə/) is a member of a family of omnivorous freshwater fish which live in South American rivers. In Venezuelan rivers they are called caribes. They are known for their sharp teeth and an aggressive appetite for meat. Description Jawbone of Pygocentrus nattereri Piranhas are normally about 15 to 25 cm long (6 to 10 inches), although reportedly individuals have been found up to 43 cm (18.0 inches) in length. Serrasalmus, Pristobrycon, Pygocentrus, and Pygopristis are most easily recognized by their unique dentition. All piranhas have a single row of sharp teeth in both jaws; the teeth are tightly packed and interlocking (via small cusps) and used for rapid puncture and shearing. Individual teeth are typically broadly triangular, pointed, and blade-like (flat in profile). There is minor variation in the number of cusps; in most species the teeth are tricuspid with a larger middle cusp that makes the individual teeth appear markedly triangular. The exception is Pygopristis, which has pentacuspid teeth and a middle cusp that is usually only slightly larger than the other cusps. In the scale-eating Catoprion, the shape of their teeth is markedly different and the premaxillary teeth are in two rows, as in most other serrasalmines. Ecology Ecologically, piranhas are important components of their native environments. Although largely restricted to lowland drainages, these fishes are widespread and inhabit diverse habitats within both lotic and lentic environments. Some piranha species are abundant locally and multiple species often occur together. As both predators and scavengers, piranhas influence the local distribution and composition of fish assemblages. Certain piranha species consume large quantities of seeds, but unlike the related Colossoma and Piaractus, herbivorous piranhas thoroughly masticate and destroy all seeds eaten and consequently do not function as dispersers. The piranha is renownedly portrayed and known as a vicious species of fish hunting in large schools. This conception was created from the past belief that piranhas created schools for hunting purposes. Recent research, however, suggests that this is actually used as a defense mechanism against the piranha’s natural predators, such as river dolphins, caimans and gigantic arapaima. Research on the species Serrasalmus aff. brandtii and Pygocentrus nattereri in Viana Lake, which is formed during the wet season when the Rio Pindare (a tributary of the Rio Mearim) floods, has shown that these species eat vegetable matter at some stages in their life; they are not strictly carnivorous fish.

]]> http://hbkman.wordpress.com/2008/10/23/piranha/feed/ 0 hbkman Jawbone of Pygocentrus nattereri http://hbkman.wordpress.com/2008/10/23/trout/ http://hbkman.wordpress.com/2008/10/23/trout/#comments Thu, 23 Oct 2008 13:18:34 +0000 hbkman http://hbkman.wordpress.com/?p=29 ]]>

Rainbow trout, Oncorhynchus mykiss

Biwa trout (or Biwa salmon), Oncorhynchus masou rhodurus

Trout is the common name given to a number of species of freshwater fish belonging to the Salmonidae.

Species

All fish called trout are members of the subfamily Salmonidae. The name is commonly used for species in three of the seven genera in the sub-family: Salmo,Atlantic species; Salvelinus,which includes fish also sometimes called char or charr. Pacific species; Oncorhynchus, Fish referred to as trout include:

• Genus Salmo
  • Adriatic trout, Salmo obtusirostris
  • Brown trout, Salmo trutta
  • Flathead trout, Salmo platycephalus
  • Marmorata, Soca River trout or Soča trout – Salmo trutta marmoratus
  • Ohrid trout, Salmo letnica
  • Sevan trout, Salmo ischchan

• Genus Oncorhynchus
  • Apache trout, Oncorhynchus Apache
  • Eskimo trout, Oncorhynchus inupiat^{[verification needed]}
  • Seema, Oncorhynchus masou
  • Cutthroat trout, Oncorhynchus clarki
    The cutthroat trout has 14 recognized subspecies (depending on your sources), such as the Lahontan cutthroat trout, Oncorhynchus clarki henshawi, Bonneville cutthroat trout, Oncorhynchus clarki utah, Colorado River cutthroat trout, Yellowstone cutthroat trout.
  • Gila trout, Oncorhynchus gilae
  • Golden trout, Oncorhynchus aguabonita
  • Rainbow trout, Oncorhynchus mykiss
  • Mexican Golden Trout, Oncorhynchus chrysogaster and as many as eight other species or sub-species in northwest Mexico, not yet formally named.

• Genus Salvelinus (Char)
  • Arctic char, Salvelinus alpinus
  • Aurora trout, Salvelinus fontinalis timagamiensis
  • Brook trout, Salvelinus fontinalis
  • Bull trout, Salvelinus confluentus
  • Dolly Varden trout, Salvelinus malma
  • Lake trout, Salvelinus namaycush
  • Silver trout, † Salvelinus fontinalis agassizi (extinct)

Habitat

A trout farm in Sochi, Russia.

Trout are usually found in cool (50-60°F, 10-15°C), clear streams and lakes, although many of the species have anadromous strains as well. Young trout are referred to as troutlet or troutling. They are distributed naturally throughout North America, northern Asia and Europe. Several species of trout were introduced to Australia and New Zealand by amateur fishing enthusiasts in the 19th century, effectively displacing and endangering several upland native fish species. The introduced species included brown trout from England and rainbow trout from California. The rainbow trout were a steelhead strain, generally accepted as coming from Sonoma Creek. The rainbow trout of New Zealand still show the steelhead tendency to run up rivers in winter to spawn.^[1] The speckled trout, found in the Gulf of Mexico and other places in the United States, is not in fact a trout at all, but a member of the drum family.

Rainbow trout, Oncorhynchus mykiss

Golden trout, Oncorhynchus aguabonita

Trout Consumption

Sharks are fishes who have some of the largest sizes as compared to all aquatic life. Sharks come in all sizes, ranging from twenty two centimeters, and aptly named the pygmy shark to the largest fish in the world, the whale shark.

The Whale Shark scientific name Rhinocodon typus is from the family Rhincodontidae and genus Rhinocodon. It is of the class Chondrichthyes and subclass Elasmobranichii. It is believed to trace it’s origins some sixty million years ago. The Whale shark is the largest living fish species.

The Whale Shark is feeds by straining food particles from water and therefore is termed as a filter feeder or a suspension feeder. They typically pass water or a specialized structure to feed. The mouth of the Whale Shark measure up to five feet. It’s mouth can contain up to three hundred and fifty rows of teeth. The shark has a flat and wide head and its eyes are located towards the front of the head.

Its body is mostly grey and it has a white patch on its belly. The whale shark is characterized by the three prominent ridges that run along each side of its body. It also has a checkerboard pattern of yellow spots and stripes.The whale shark has two pairs of pectoral and dorsal fins. Its skin can be up to ten centimeters thick.

This size makes the whale shark the biggest fish in the world. However, the whale shark uses its entire body for swimming, and therefore, it is not as good a swimmer as compared to other sharks and fishes. This unusual trait gives the whale shark a unimpressive speed of about five kilometers per hour.

The Whale Shark normally inhabits the warm temperature and tropical climates. It was first identified in the year 1828, with the harpooning of a fifteen feet long member of the species in Table Bay, South Africa. The Whale Shark is the largest specimen of aquatic life ever caught.

The largest fish ever caught was caught on November 11, 1947 near the island of Baba. It was about forty two feet long and weighed more than twenty tonnes. It had a girth of about twenty three feet.

Though the whale shark is the largest shark ever, it is a misunderstood predator. It’s massive size creates a illusion about the dangers to humankind, however, the whale shark does not pose any significant danger to uses. Whale Sharks are not man-eaters and can actually be playful and gentle with divers. The whale shark attacks humans only when provoked, and divers can actually dive alongside this great fish, with the only risk of being accidentally heat by its large tail fin.

The whale shark feeds on squids, other aquatic vertebrates, drifting aquatic organisms known as phytoplanktons, planktons, macro-algae and krill. Contrary to popular belief, their immense rows of teeth play no role in their feeding. The shark gulps in a mouthful of water and then exhales the water through its gills. The plankton is trapped in the whale shark’s mouth during this procedure. The whale shark also has a sieve like apparatus, which is unique to the whale shark. This prevents the escape of anything except fluid through the gills. The whale shark can therefore trap anything up to three millimeters.

There have been many rumors about the size of the whale shark and the largest fish ever caught or seen. Some claims even say that whale sharks the size of about seventy five feet have been found. One famous rumor is about the ship Maurguni, which rammed against a whale shark, which resulted in the whale being stuck in the prow of the ship, being four to five meters on one side and about thirteen meters on the other.

Least Concern

Physical description

Largemouth from San Marcos River, Texas.

The largemouth is marked by a series of dark, sometimes black, blotches forming a jagged horizontal stripe along each flank. The upper jaw (maxilla) of a largemouth bass extends beyond the rear margin of the orbit. The largemouth is the largest of the black basses, reaching a maximum recorded overall length of (38 in/97 cm) and a maximum recorded weight of 25 pounds (11.3 kg). The fish lives 16 years on average.

Forage

The juvenile largemouth bass consumes mostly small bait-fish, scuds, and insects. Adults consume smaller fish, crawdads (crayfish), frogs, snakes, salamanders, bats and even small water birds, mammals, and baby alligators^[8]. In larger lakes and reservoirs, adult bass occupy deeper water than younger fish, and shift to a diet consisting almost entirely of smaller fish like shad, trout, ciscoes, shiners, and sunfish. Prey items can be as large as 25 to 35% of the bass’s body length. Studies of prey utilization by largemouths show that in weedy waters, bass grow more slowly due to difficulty in acquiring prey. Less weed cover allows bass to more easily find and catch prey, but this consists of more open-water baitfish. Paradoxically, with little or no cover, bass can devastate the prey population and starve or get stunted. Fisheries managers need to take all these factors into consideration when designing regulations for specific bodies of water. Under overhead cover such as overhanging banks, brush, or submerged structure such as weedbeds, points, humps, ridges, and drop-offs, the largemouth bass will use its senses of hearing, sight, vibration, and smell to attack and seize its prey. It can sometimes hold up to 5 sunfish in its mouth. Adult largemouth generally are apex predators within their habitat, but they are preyed upon by many animals while young.

On November 27th a dive was planned to 115 m with a 15 minute bottom time; the divers were Pieter Venter, Gilbert Gunn and cameramen Christo Serfontein and Dennis Harding. The support divers were Pieter Smith, Martin Bensch and Etienne le Roux. After searching caves along the wall of the canyon for 12 minutes, three coelacanths were sighted and filmed with the video camera (Figs 2 & 3) at a depth of 108 m. The largest fish was between 1.6 and 1.8 m in length, and the other two coelacanths were about 1.5 and 1.0 m. The water temperatures at the bottom for the October and November dives were 17C and 18C respectively.

After 15 minutes, the divers started their ascent as planned, but at a depth of 70 to 60 m, some problem involving Harding and Serfontein resulted in their uncontrolled ascent to the surface. Harding lost consciousness soon after surfacing and was rushed to the beach. Efforts to resuscitate him were unsuccessful. Serfontein was also unconscious when he reached the surface, but with the assistance of Pieter Smith, he regained consciousness and was able to descend immediately to a depth of 32 m to resume his decompression schedule. After 134 minutes in the sea, Serfontein was taken to the beach, administered oxygen and transported to Richards Bay for 6 hours of treatment in a decompression chamber.

DISCUSSION

The fossil record of coelacanths,[2] comprising some 120 species arrayed in about 47 genera and three or four families, extends from the Middle Devonian (380 million years ago) to the end of the Cretaceous (70 million years ago), when the coelacanths were thought to have died out, along with the dinosaurs and many other fossil groups. The first fossil coelacanth was described in 1836, and the group is now well known in the literature on
fossil fishes. The genus name Coelacanthus (meaning “hollow spine”) refers to the hollow neural and haemal spines of the vertebrae that connect to the tubular pterygiophores supporting the dorsal and ventral caudal fin
rays [3]. Three extinct species are known from South African fossils, one in KwaZulu-Natal, one from the Free State, and one from Grahamstown [2,4]. Most fossil coelacanths are known from marine deposits, but a few were adapted to freshwater. They attained their maximum diversity (in number of species) in the Triassic Period (some 200 million years ago), but disappeared from the fossil record at the end of the Cretaceous [2]. Consequently, the zoological world was astounded when a living coelacanth (Latimeria chalumnae Smith, 1939) was discovered off the Chalumna River near East London[5] in December 1938. Coelacanths have changed little over the past 380 million years. The skeleton of Macropoma mantelli, which is known from the Upper Cretaceous, is virtually identical to that of the living coelacanth and differs little from the skeleton of most Devonian coelacanths [2].

Although only a single specimen of Latimeria chalumnae has been caught off South Africa, the discovery of this first specimen did much to put South Africa and J.L.B. Smith on the ichthyological map of the world. Thanks to
the efforts of J.L.B. and Margaret Smith, Marjorie Courtenay-Latimer, French anatomists, and more recently, Hans Fricke’s observations and films of coelacanths in their natural habitat at Grand Comoro, we have learned much about this fascinating fish [6-10]. Since 1952, when the “home” of the coelacanth was discovered in the Comoros, more than 180 coelacanths have been caught with hook and line in depths of 35– 600 m on the steep volcanic slopes of Grand Comoro and Anjouan Island [8,9]. A gravid coelacanth was trawled off the central coast of Mozambique [10] and a specimen was also caught in a shark net near Toliara on the southwest coast of Madagascar [11]. The recently discovered coelacanths near Manado at the northern end of Sulawesi, Indonesia seem to be a
separate species [12].

In May 1991, a project organised by Prof M.N. Bruton (then Director of the J.L.B. Smith Institute of Ichthyology) brought Prof Hans Fricke and his submersible JAGO to South Africa to look for coelacanths and survey the faunal diversity in depths of 50-400 m along the coast of the Eastern Cape Province Fifteen dives totalling 23h 45 min were carried out at depths of 35-110 m in the Tsitsikamma National Park on the Eastern Cape coast, and 8 dives totalling 23h 30 min were done to depths of 370 m on the continental shelf and slope off the Chalumna River Mouth. No coelacanths were sighted during the survey, nor were large caves seen off the Chalumna River, as the friable sandstone terraces of the slope in this region is not conducive to formation of caves; in several places, the roofs of overhangs were seen to have collapsed after being eroded too far.

The continental shelf off the coast of northern KwaZulu-Natal is narrow (approximately 3 km wide, with a shelf break at –45 to –70 m, and along this coast there are some 13 canyons that begin at depths of –30 to –40 m
within 1 or 2 km of shore and plunge to depths of –650 m within 8 km of shore.[13] The beachrock/aeolianite walls of the Jesser Canyon where the Sodwana coelacanths were sighted are evidently more sturdy and suited to cave formation than the slope sedimentary rock off the Chalumna River. The sheltered habitat of this V-shaped canyon is also less exposed to the strong Agulhas Current than the lower relief slope off the Eastern Cape Province. The similar canyons along the coast of northern KwaZulu-Natal and Mozambique are also likely to be suitable habitat for coelacanths.

Because of the difficulty in sampling and observing fishes in rough bottom habitats below depths of 50 m, the fish fauna of these habitats is poorly known. This discovery of a small population of coelacanths at a depth of 104 m at Sodwana Bay, a popular dive site in South Africa, emphasises how little we know about life in the oceans and the need for further exploration and survey work to assess the fish diversity of southern Africa and the Western Indian Ocean.

The sighting of juvenile (1 m) and adult (1.6 to 1.8 m) coelacanths on two separate dives implies a viable population of Latimeria chalumnae in a marine protected area (St Lucia Marine Reserve), and this is good news for the conservation of this apparently endangered species. The Minister of the Department of Environmental Affairs and Tourism has acted swiftly to legislate for the protection of the population, and a management plan is being prepared by the KwaZulu-Natal Nature Conservation Service in collaboration with the Marine and Coastal Management division of the Department of Environmental Affairs and Tourism.

We express our condolences to family and friends of our fellow diver, Mr Dennis Harding. We are grateful to Mr André Slade of Inner Space Developments, for the use of his underwater video equipment. We thank Robin Stobbs. M.N. Bruton and Eric Anderson for their useful comments on the manuscript.