17
Fishes

Fishes. Classification of Fishes Three classes of vertebrates: Agnatha; Chondrichthyes; and Osteichthyes Fishes are the most numerous of all vertebrates

Embed Size (px)

Citation preview

Fishes

Classification of Fishes

• Three classes of vertebrates: Agnatha; Chondrichthyes; and Osteichthyes

• Fishes are the most numerous of all vertebrates and most widespread in their distribution

Adaptations• Because water is 800 times the density of air, it affects both the body and

mobility of fishes: adaptation for buoyancy (trapping of gas inside their body: gas bladder in order to regulate their vertical position)

• Ability to swim: a streamlined shape and muscular tail enables them to move rapidly through the water; paired fins allow them to maneuver easily left or right, up or down, and backward and forward; the mucus reduces friction

• Scales limit chemical exchanges through the skin; exchanges occur through the membranes of the gills: the external respiratory organs

• Lateral line system: consists of a row of sensory structures that run the length of the body and connected by nerves to the brain; detects vibrations.

Osteichthyes• Osteichthyes make up most of the vertebrate

population in fresh water and in salt water. • Lobe-finned fishes, or coelacanths, have paddle like

fins with fleshy bases. • Lungfishes have gills where gas exchange takes

place between water and the blood. They burrow unto the mud and cover themselves in mucus to stay moist until the pond refills.

• Ray-finned fishes have fins that are supported by the long bones called rays. They are the most familiar fishes and include snakelike eels, yellow perch, cave fish, herring, and lantern fish.

Morphology of a Bony FishExternal AnatomyBody Structure• Distinct head, trunk, and tail regions• Each side of head is operculum

-Hard plate that opens at rear and covers and protects gills

• Strong muscles along dorsal backbone thrust tail from side to side

Fins• Thin fan-shaped membranes

• Richly supplied with blood

• By raising and lowering fins, regulate body temperature

• Supported by rays or spines-Rays- bony yet flexible-Spines- bony and rigid

• Adapted for swimming and guiding fish through water

• Caudal fin extends from tail-Moves from side to side and amplifies swimming motions

• 2 dorsal fins, one anterior and one posterior, and ventral anal fin-Help keep fish upright and moving in straight line

• Paired pelvic fins and pectoral fins-Used to steer, brake, move up and down, and even back up-Orient body when at rest

The Median FinsThere are four median, unpaired fins.  These are:  the caudal fin, just seen; the anal fin, located posterior to the anus; the anterior dorsal fin, beginning at the anterior end of the trunk; and the posterior dorsal fin, located posterior to the anterior dorsal fin.

TailTapering from the trunk, the tail ends as a laterally compressed paddle. The symmetrical caudal fin surrounds the fleshy end of the tail. This type of symmetrical caudal fin is correlated with the presence of a swim bladder.

More on Fins & Tails

ScalesAlmost all fish have scales. Scales are transparent plate-like structures covering the body usually in an overlapping fashion (sort of like the shingles on a roof). There are four types of scales: Cycloid, Ctenoid, Placoid and Ganoid.

True bony fish have ctenoid or cycloid scales. Ctenoid scales are rough in texture because they have tiny teeth along their edges. Cycloid scales on the other hand have a smooth surface. Fish such as bass, perch and snappers have ctenoid scales (their skin is rough to the touch) and cycloid scales can be found on fish such as carp, salmon, herring and sardines.

Ganoid scales are found on more primitive bony fishes such as gars and sturgeon. These scales are diamond shaped. The rows of bony scutes on a sturgeons body are modified ganoid scales.

Sharks, skates and most rays have placoid scales which are rough and sharp. Placoid scales which are also referred to as dermal denticles, look like tiny teeth.Some primitive fish do not have scales at all. Their bodies are smooth and slimy.

Did You Know?... The scales of some fish can tell scientists how old fish are. By looking under a microscope scientists can see growth rings on the scales which represent a season or period of active growth for the fish.

Figure 1: External Anatomy of the Perch (Lateral View).

Internal AnatomyDigestive System

Find the following internal organs:• a)  Esophagus - located at the extreme anterior end of the body cavity, the esophagus is a

short, straight tube leading from the oropharynx to the stomach.• b)  Stomach -the stomach is a larger, thick-walled U-shaped tube.  In the perch breakdown

of the food by mechanical and chemical means, begins in the stomach.  The size of the stomach varies according to how much food it contains.

• c)  Pyloric caeca - the junction of the stomach and the intestine is marked by the presence of three pyloric caeca.  These are blind-ended tubes extending from the gut that serve secretory and absorptive functions.

• d)  Intestine - originating at the stomach, the intestine forms an S-shaped loop.  At the end of the loop the intestine constricts and straightens.  The intestine extends directly to the anus.  The perch's intestine is less than the length of its body. This correlates with the animal's carnivorous life style.  Herbivorous fish have an intestine, which is longer (2 to 15 times the body length).  A longer intestine is required to provide greater digestive and absorptive surfaces for the herbivores.

• e)  Liver -situated just anterior to the stomach. On the undersurface of the liver is the gall bladder.  The gall bladder drains bile from the liver, and opens by a number of ducts into the intestine.  Bile is necessary for the proper digestion of fats.

• f)  Pancreas -the pancreas is a digestive gland, usually found along the ventral border of the intestine.  In some fish the pancreas is embedded in the liver.  The pancreas secretes digestive enzymes into the intestine and hormones (insulin and glucagons) into the blood.

• g)  Spleen- lying on the posterior dorsal surface of the stomach, the spleen is a football shaped organ.  It functions in the production and maintenance of blood cells.

Figure 2:  Perch internal anatomy.

Gill Structure

Circulatory System

• Adapted for rapid swimming and other high-performance activities

• Consists of:-Two-chambered heart

1. Atrium- collecting chambers2. Ventricle- pumping chambers

-Blood vessels-Blood containing red and white blood cells

• Heart pumps blood through arteries to small, thin-walled vessels called capillaries in gills blood picks up oxygen gas from releases carbon dioxide into water blood moves to body tissues, where nutrients and wastes are exchanged blood returns to heart through veins

Respiratory and Excretory Systems• Gills adapted for gas exchange

• Consists of four sets of curved pieces of bone on each side of head

• Each has double row of thin projections called gill filaments richly supplied with capillaries

• Large surface area allows rapid gas exchange

• Excrete nitrogenous wastes from body, but task carried out primarily by kidneys

• Kidney’s filter out dissolved chemical wastes from blood

Swim Bladder

• Swim bladder or gas bladder

-Thin-walled sac in abdominal cavity

-Contains mixture of oxygen, carbon dioxide, and nitrogen obtained from bloodstream

-By regulating amount of gas in sac, fish adjust overall density and thus move up or down in water or hover at given depth

Reproduction

• Sexes are separate

• Eggs produced by ovaries in female; sperm produced by testes in male; both released through opening just rear of anus

• Fertilization of eggs takes place externally

• Young fish hatch within hours of warm water or after many weeks in cold water

• Number of eggs bony fish may lay varies considerably

• Some bear live young

• Female may receive sperm during mating, and fertilization in some is internal and other species it is external

• Carries eggs in body until young are born

• Spawn- reproduce