Wednesday, 2 July 2008

Fish Respiration


In order to live, fish must extract oxygen from the water and transfer it to their bloodstream. This is done by gills, lungs, specialized chambers, or skin, any of which must be richly supplied with blood vessels in order to act as a respiratory organ. Extracting oxygen from water is more difficult and requires a greater expenditure of energy than does extracting oxygen from air. Water is a thousand times more dense (heavier per unit volume) than air, and at 20 deg C (68 deg F) it has 50 times more viscosity (resistance to flow) than air and contains only 3% as much oxygen as an equal volume of air. Fishes, therefore, have necessarily evolved very efficient systems for extracting oxygen from water; some fishes are able to extract as much as 80% of the oxygen contained in the water passing over the gills, whereas humans can extract only about 25% of the oxygen from the air taken into the lungs.

Gills are made efficient in a number of ways.
1) A large surface area for gaseous exchange means that more oxygen can enter the bloodstream over a given period of time. A single gill of a bony fish consists of a curved gill arch bearing a V-shaped double row of gill filaments. Each filament has many minute folds in its surface, giving it a sort of fuzzy appearance and increasing the amount of surface area along a given length of filament. Consequently, the surface area of the gills is commonly 10 to 60 times more than that of the whole body surface :
2) A short diffusion, or travel, distance for the oxygen increases the rate of oxygen entry into the blood. The blood traveling in the folds of the filaments is very close to the oxygen-containing water, being separated from it by a very thin membrane usually 1 to 3 microns (4/100,000 to 1/10,000 in) thick, and possibly less.
3) By using countercurrent circulation in the gill, the blood in the filament folds travels forward, in the opposite direction to the water flow, so that a constant imbalance is maintained between the lower amount of oxygen in the blood and the higher amount in the water, ensuring passage of oxygen to the blood. If the blood were to flow in the same direction as the water, oxygenated blood at the rear of the gills would be traveling with deoxygenated water and not only could not extract oxygen from the water but would even lose oxygen to it.
4) Gills have little physiological dead space. The folds of the filament are close enough together so that most of the water passing between them is involved in the gas-exchange process.
5) Water flows continuously in only one direction over the gills, as contrasted with the interrupted, two-way flow of air in and out of lungs of mammals.

Fish circulation


The blood of the fish serves, as does the blood of other vertebrates, to transport oxygen, nutrients, and wastes. The typical fish's circulation is a single circuit: heart-gills-body-heart. In contrast, mammals have two circuits: heart-lungs-heart and heart-body-heart. The fish heart proper is two-chambered, consisting of an upper atrium and a lower ventricle. Amphibians, basically, have a three-chambered heart, two atria and one ventricle; reptiles have a three- or four-chambered heart; and mammals and birds have a four-chambered heart consisting of two atria and two ventricles. The fish heart, however, has two accessory chambers, and all four chambers are contained within a single pericardial sac. One accessory chamber is the thin-walled sinus venosus, which collects blood and leads into the atrium; the other accessory chamber is the conus arteriosus, an enlargement of the main artery leading out of the ventricle. In some fishes, such as sharks, the conus arteriosus is muscular and pumps blood in the manner of the ventricle.

Fish Anatomy


The living species of fish are usually divided into three classes: the Agnatha, the jawless fishes, comprising the hagfishes and lampreys; the Chondrichthyes, the cartilaginous-skeleton fishes, such as sharks and rays; and the Osteichthyes, the bony-skeleton fishes, comprising all other living fishes. The skeletons of these three groups vary in fundamental ways. In the hagfishes and lampreys the backbone is basically a notochord, a rodlike structure composed of unique notochordal tissue. In sharks and rays the notochord is surrounded and constricted by spaced rings of cartilage, the vertebrae, to form a backbone. The remainder of the skeleton is also cartilaginous, not bony, but in many forms the cartilage is partly calcified, and thereby hardened, by the addition of calcareous salts. In primitive bony fishes, such as the sturgeon, the vertebrae spaced along the notochord are still largely cartilaginous, but in most advanced bony fishes the vertebrae are bony and are united to form the backbone, and the notochord is no longer present.

Some fishes, such as lampreys, lack ribs; others have either a single or a double pair of ribs attached to each trunk vertebra. Among the higher bony fishes there also may be small, riblike intermuscular bones, which often render such fish difficult to eat.

The body appendages of fish are of two kinds, cirrhi and fins. Cirrhi are flaps of flesh that may appear on any part of the body; they often serve as camouflage. Fins are either median or paired. Median fins are situated along the centerline of the body, at the top, the bottom, and the end. The top, or dorsal, fin may consist of one to several fins, one behind the other, and may include a fleshy fin, called the adipose fin, near the tail. The bottom, or anal, fin is located on the belly behind the vent, or anus. The end fin is called the tail, or caudal, fin.

The dorsal and anal fins may be supported by cartilaginous rods, as in the lampreys, by cartilaginous rods and horny rays, as in sharks, by horny rays, as in the spiny-finned fishes, or by bony rays (derived from scales) in the soft-rayed fishes. The tail fin may be protocercal, the body continuing straight back as a middle support between the upper and lower lobes of the tail; heterocercal, with the end of the body turning up and continuing to the tip of the upper lobe; or homocercal, in which the last few vertebrae are fused and joined with other bony elements (hypurals) to support the tail-fin rays. A modification of the heterocercal tail so as to resemble the protocercal type is called diphycercal.

The paired fins correspond to the arms and legs of land vertebrates. The pectoral fins are situated at the front of the body behind the gill openings and generally function to provide maneuverability, but may be highly modified to fulfill other functions. The simplest internal support for the pectoral fins occurs in the sharks, where a U-shaped cartilaginous skeletal structure, called the pectoral girdle, joins and helps support the two pectoral fins. In the higher bony fishes the pectoral girdle is composed of bone and is more complex in structure. The pelvic fins, also called the ventral fins, are located along the bottom of the body but vary considerably in their placement. They may be located in the middle of the belly, as in salmon; below the pectorals, as in the largemouth bass; or in front of the pectorals, as in cods. Pelvic fins also serve as maneuvering structures and also may be modified to serve other uses. The supporting pelvic girdle is lacking in many bony fishes; in most fishes in which the pelvic girdle is present it is represented by a single skeletal element on each side of the body.

The scales of fish are colorless; a fish's coloring arises from structures beneath or closely associated with the scales. Not all species of fishes have scales, or the scales may be so small as to make the fish appear scaleless. Scales also may be present only on small areas of the body. The arrangement of scales may be imbricate (overlapping like the shingles on a roof) or mosaic (fitting closely together or just minutely separated).

Four basic scale types can be distinguished on the basis of structure. Placoid scales, also called dermal denticles, are found on sharks and rays and are toothlike in structure. Indeed, modified and enlarged placoid scales have become the teeth of sharks. The placoid scale consists of an upper layer of enamellike substance called vitrodentine, a lower layer of dentine, a pulp cavity, and a disklike basal plate embedded in the skin. Placoid scales do not increase in size as do the scales of bony fishes, and new scales must be added as a shark grows.

Cosmoid scales are found on the primitive coelacanth. They also occur on lungfishes, but in a highly modified, single-layered form. The cosmoid scale of the coelacanth is a four-layered bony scale. The upper layer is enamellike vitrodentine; the second layer is a hard, dentinelike substance called cosmine; the third layer is spongy bone, and the lowest layer is dense bone.

Ganoid scales, as found on gars, are typically squarish (rhombic) in shape and consist of a single bony layer, a layer of cosmine, and a covering of a very hard enamellike substance called ganoin.

Leptoid scales are believed to have been derived from ganoid scales by the loss of the ganoin layer; they consist of a single layer of bone. Leptoid scales are found on the higher bony fishes and occur in two forms: cycloid (circular) and ctenoid (toothed), the latter bearing tiny comblike projections. The single-layered cosmoid scale of lungfishes also may be classified as leptoid, although of a different derivation.

Collision leaves child orphaned, in coma

By : Alina Simon
PASIR PUTIH: A 5-year-old girl lies in the intensive care unit of the Raja Perempuan Zainab II Hospital in Kota Baru, unaware that she has lost her parents, both brothers and an unborn sibling in an accident.
Nik Nurul Analia Balkis Mohd Rudi is in a coma with severe internal bleeding of the brain and a broken leg suffered when a collision between two cars on Monday plunged both vehicles into a metre-deep drain.Those killed were Perodua Kancil driver Mohd Rudi Abdul Latif, 33, his three-month pregnant wife Raja Rossini Raja Hussin, 26, and their sons Nik Anas Mohd Haikal, 7, and Mohd Imram Hashimi, 3. The driver of the Proton Perdana V6, which hit them as he tried to overtake, is also in a coma in the same hospital as the child.Furniture shop owner Che Othman Che Hussin, 41, who is from Melor, suffered head injuries and broken ribs and legs.
Raja Rossini's mother, Mariah Yusuf, said that Nik Nurul Analia Balkis had been fussing during a visit to her home in Kampung Jerat Semata so Mohd Rudi decided to take his family for a drive about 4pm to pacify her.Said Mariah: "We don't know how to tell Nurul that her papa, Umi, Along and Baby (Imram) are no more. She's a bright girl but she's still a little girl. Her condition is serious and the doctors have not allowed us to see her just yet."We have not discussed it with the in-laws, but one of my daughters is willing to take Nurul in because she is childless." The four were buried yesterday in one grave in Kampung Gaal Hilir, where Mohd Rudi's family home is.


With more than 29,000 species, fishes are the most diverse group of vertebrates on the planet. Of that number, more than 12,000 species are found in freshwater ecosystems, which occupy less than 1 percent of the Earth’s surface and contain only 2.4 percent of plant and animal species. But, on a hectare-for-hectare basis, freshwater ecosystems are richer in species than more extensive terrestrial and marine habitats. Examination of the distribution patterns of fishes in these fresh waters reveals much about continental movements and climate changes and has long been critical to biogeographical studies and research in ecology and evolution.

All fishes are vertebrates (Subphylum Vertebrata), which means that they have a backbone. Fishes are a very diverse group, but the major characteristics of fishes are that they 1) live and grow in water, 2) swim with fins, and 3) use grills for gas exchange (breathing). There are three classes of fishes; the jawless fishes, the cartilaginous fishes, and the bony fishes. As their name suggests, jawless fishes do not have lower jaws, and typically suck onto their prey using hook like teeth. The cartilaginous fishes are the sharks and rays. They do not have a calcified bony skeleton like ours, but rather a more flexible skeleton made of cartilage, like what our ears and noses are made of. Sharks have a very large oil-filled liver that helps them to remain buoyant in the water column. The bony fishes are the most diverse and abundant class of fishes. They have a calcified bony skeleton like ours and use a special gas-filled organ, the swim bladder, for buoyancy. The more gas the fish pumps into the bladder, the more buoyant it is. This is analogous to a human taking a deep breath of air, the more air in the lungs, the better you float in the water. Of course, fishes do not want to float on top of the water, but the idea of having greater buoyancy after more air is the same. Some fast swimming fish, like mackerel, that may move up and down in the water column very quickly, do not use a swim bladder, but rather use oil for buoyancy (if you have ever eaten mackerel you may have noticed that it is a particularly oily fish). The external anatomy of a fish is very different from our own, because fishes are adapted to move and live in water, and we are adapted to live on land. Therefore, locomotion and sensory structures may look very different, although their general functions are very similar. For example, fishes have “noses” (called nares) that don’t look anything like our own, yet their purpose is to smell chemicals in the water. Likewise, the internal anatomy will look very different from our own, however, most of the major organs are the same (e.g., heart, stomach, liver, spleen) and have the same basic function. A few internal structures, like the swim bladder, are of course unique to fishes. In this lesson we will be examining the external and internal anatomy of a bony fish and comparing this to a human. Fishes do have a few specialized structures that have no counterpart to humans. The lateral line is one example. The lateral line detects physical vibrations in the water that allows the fish to sense other animals and objects in the water, even if they can’t be seen. Many types of fishes use inner ear stones, called otoliths, to detect changes in body position. Because of their unique characteristics and growth patterns, scientists often use otoliths to classify fish, as well as determine their age. These stones rest on a bed of sensory hairs, that send messages to the brain about the orientation of the fish. Sharks have an organ in their snout, called the impullae of Lorenzini, that detects weak electric fields. It is thought that they use this structure to detect prey, perhaps being able to distinguish the weak electrical signals given off by injured animals.


Biodiversity is the quantity, variety and distribution across biological scales ranging through genetics and life forms of populations, species, communities and ecosystem. Biodiversity affects the capacity of living systems to respond to changes in the environment, underpins ecosystem function and provides the ecosystem goods and services that support human well-being (e.g., nutrient cycling, clean water. As well as having intrinsic value, biodiversity has aesthetic value: many of us have admired the wonderful colors and shapes of fishes on coral reefs and in other coastal habitats. Some benefits of biodiversity are not apparent today but may be unlocked in the future (known as the option value): compounds derived from marine animals and plants may serve as medicine to prevent and cure more of our ills in the future. Biodiversity also has cultural value when it is directly linked to the cultural fabric of human societies.

Human efforts, especially over the past 50 years, to meet rapidly growing demands for food, fresh water, timber, fiber, and fuel have resulted in an array of extensive changes to terrestrial, freshwater, and marine ecosystems. These changes, in turn, have resulted in an ongoing, widespread, and largely irreversible loss in the number and variety of organisms on Earth as well as the degradation of ecosystem services. The effects of pressures that arise from social and economic aspirations have been particularly severe on freshwater ecosystems. An index of the world’s freshwater species shows a more rapid decline between 1970 and 2000 than for terrestrial and marine indices during the same period. Similarly, South Africa’s first National Spatial Biodiversity Assessment examined the terrestrial, river, estuarine, and marine environments, and highlighted the fact that the country’s river ecosystems are now in a much poorer state overall than its terrestrial ecosystems.

Protected Areas represent one management instrument to balance the conservation and use of natural resources.

Fish species can be divided into at least eight group of feeding guilds (based on Inger and Chin, 1962), although it should be remembered that some species change their dietry preferences with age, season, and with the availability of alternative food items.

It can be difficult to determine directly what a particular fish has been feeding on. The gut of a fish may frequently be empty, but some indication of diet can be gain by examining the length of the gut in the relation to the length of the body. Thus herbivore generally have a gut which is 4-10 times the length of the body, whereas predator guts are much straighter and may be only as long as or even shorter than the body.

This technique can be useful to differentiate between herbivoures that fed on microscopic plants, filamentous algae etc. and primary predator that feed on nematode worm and other small animal living in the sediment. Both types of fish generally have stomach filled with mud or sand, but the gut length to body length ratio provide a guide to their preferred food.

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