FISH

FISHIsabella M, Taylor W, Rachel W

Cartilaginous Fish (Chondrichthyes) notochord is present in young, but is

replaced by cartilage in adults red blood cells are produced in the

spleen, rather than bone marrow paired appendages tooth-like scales, called denticles

Characteristics

Jawless Fish (Agnatha) seven pairs of gill pouches no scales, only skin lack paired appendages have a notochord

Characteristics

Bony Fish (Osteichthyes) endochondral bone replaces

cartilage calcified bones circulatory system in the bones

creates osteoblasts, which continually replace and strengthen the bones

sclerotic ring supports the eyeball

Characteristics

The first fish were the Ostracoderms which appeared during the Cambrian period to the end of the Devonian period (530 million years ago – 350 million years ago)

Jawless fish found in fresh water Mostly covered with bony armor or

scales The Ostracoderms are placed in the

class Agnatha along with the living jawless fishes, the lampreys and hagfishes, which are believed to be descended from the Ostracoderms.

Evolution of Ostracoderms

Ostracoderms

Appeared in the late Silurian period and became extinct before the end of the Permian period (410 million years ago – 250 million years ago)

First fishes with jaws and they were generally small shark like fishes varying from toothless filter-feeders to toothed predators

It is commonly believed that the Acanthodians and the modern bony fishes are related and that either the acanthodians gave rise to the modern bony fishes

Evolution of Acanthodians

Acanthodians

Appeared at the beginning of the Devonian period and became extinct at the end of the Devonian period or the beginning of the Mississippian period (395 million years ago – 345 million years ago)

Typically small, flattened bottom-dwellers.

Evolution of Placoderms

Placoderms

Appeared in the middle of the Devonian period

Generally believed to be descended from the bony-skeleton Placoderms.

The cartilaginous skeletons are considered to be a later development.

Evolution of Chondrichthyes

Chondrichthyes

Appeared in the late Silurian period or early Devonian period (395 million years ago)

Modern bony fish The early forms were freshwater fishes The Osteichthyes may have arisen

from the acanthodians

Evolution of Osteichthyes

Osteichthyes

Appeared in the late Silurian period or early Devonian period (390 million years ago)

Characterized by internal nostrils, fleshy fins called lobe fins, and cosmoid scales

The choanate fishes include a group known as the Crossopterygii, which has one living representative, the coelacanth Latimeria. During the Devonian Period some crossopterygian fishes of the order (or suborder) Rhipidistia crawled out of the water to become the first amphibians.

Evolution of Choanichthyes

Choanichthyes

• Group Agnatha includes Lamprey and Hagfish (jawless)

• Subphylum Hyperotreti: skull consists of cartilaginous bars; jawless; no paired appendages; mouth with 4 pairs of tentacles; olfactory sacs open to mouth cavity; 5 - 15 pairs of pharyngeal slits (ex. Hagfish)

• Class Cephalasipomorphi: has sucking mouth with teeth and rasping tongue; seven pairs of pharyngeal slits; blind olfactory sacs. (ex. Lampreys)

Classification

Lamprey Hagfish

• Class Chondrichthyes: Tail fin with large upper lobe (heterocercal tail); Cartilaginous skeleton; lack opercula and a swim bladder or lungs

(ex. Sharks and Stingrays)• Class Osteichthyes: Most

with bony skeleton; operculum covers single gill opening; pneumatic sacs function as lungs or swim bladders.

(ex. Bony fishes)

Classification

Fishes move through the water using their fins and body wall to push against the incompressible surrounding water.

Muscles in fish extend posteriorly and anteriorly in a zigzag fashion, so the contraction of each muscle bundle affects a relatively large portion of the body wall.

Locomotion

The earliest fishes were probably filter feeders and scavengers

Modern fishes are predators and spend much of their lives searching for food. Their prey varies within their stages of life

As a larva, fish may feed on plankton; as an adult, it may switch to larger prey, such as annelids or smaller fish.

Nutrition and Digestive System

To capture prey, fishes often use the suction methods, capturing prey while swimming (called gill rakers), or by parasitic methods. Some fish simply feed on plants.

From there the fish digestive tract is similar to that of other vertebrates. An enlargement, called the stomach, stores the meals. The small intestine is the primary site for enzyme secretion and food digestion.

Sharks and other elasmobranchs have a spiral valve in their intestine. Bony fishes have outpockets of the intestine, called pyloric ceca.

Nutrition and Digestion cont.

All vertebrates have a closed circulatory system in which a heart pumps blood, red blood cells containing hemoglobin thorough a series of arteries, capillaries, and veins.

Circulation and Gas Exchange

In fish, the deoxygenated or oxygen deprived blood, is carried by the veins to the sinus venosus. Sinus venosus is an important constituent of the circulatory system of lower vertebrates. The deoxygenated blood collected by the veins accumulates in the sinus venosus, before entering the heart. Blood first enters the atrium of the heart, which is a large chamber. Then it enters the ventricle, from where it is pumped into the tube, bulbus arteriosus. Through bulbus arteriosus, the blood reaches the aorta and then the gills. The gills are the respiratory organ of a fish and they execute the activities performed by human lungs. They facilitate the exchange of gases, i.e. absorption of oxygen from water and elimination of carbon dioxide. Then the oxygenated blood is transported throughout the body with the help of blood vessels. Blood facilitates the transport of oxygen and nutrients. It also collects carbon dioxide which is again transported to the heart and then to the gills, to be removed from the body.

http://www.buzzle.com/articles/circulatory-system-of-a-fish.html

Fishes live in an environment that contains less than 2.5% of the oxygen present in air. To maintain adequate levels of oxygen in the bloodstream, fishes must pass large quantities of water across gill surfaces and extract the smaller amount of oxygen present in the water.

Gas exchange across gill surfaces is very efficient. Gill Visceral arches support gills

Gill filaments extend from each gill arch and include vascular folds of epithelium called pharyngeal lamelle.

Circulation and Gas Exchange cont.

Gas exchange occurs as blood and water moves in opposite directions on either side of the lamellar epithelium.

This countercurrent exchange mechanism provides very efficient gas exchange by maintaining and concentration gradient between the blood and the water over the entire length of the capillary bed.

Most bony fishes have gas chambers called pneumatic sacs.

Gas exchange cont.

The eyes of fishes are similar to other vertebrates. They are lidless, and the lenses are round

Receptors for equilibrium, balance, and hearing are in the inner ears of fishes and their functions are similar to those of other vertebrates.

Running along each side and branching over the head of most fishes is a lateral-line system. The lateral-line system consists of sensory pits in the epidermis of the skin that connect to canals that run jest below the epidermis.

Nervous and Sensory Functions

Electroreception is the detection of electrical fields that the fish or another organism in the environment generates.

Nervous and Sensory Functions cont.

As well as with all vertebrates, the excretory structures in the kidneys are called nephrons.

Nephrons filter bloodborne nitrogenous wastes, ions, water, and small organic compounds across a network of capillaries called glomerulus.

The filtrate then passes into a tubule system, where essential

Excretion and Osmoregulation

Fishes produce large amounts of eggs which increases the chances of surviving offspring.

Some fishes show mating behavior that helps ensure fertilization or nesting behavior that protects eggs from predation, sedimentation, and fouling.

Mating may occur in large schools, one individual releases eggs or sperm that often releases spawning pheromones that induce many other adults to spawn.

Reproduction and Development

Most fishes are oviparous, meaning eggs develop outside the female from stored yolk.

Some elasmobranches are ovoviviparous, and their embryos develop in a modified oviduct of the female.

In guppies, eggs are retained in the ovary, and fertilization and early development occur there. Embryos are then released into a cavity within the ovary and development continues, with nourishment coming partly from yolk and party from ovary secretions.

Reproduction and Development cont.

• Cloaca: The common cavity into which the intestinal, genital, and urinary tracts open in vertebrates

• Electroreception: The ability to detect weak electrical fields in the environment.

• Gill Arches: Bony or cartilaginous gill support of some vertebrate. (also called visceral arches)

• Gill filament: A thing walled, fleshy extension of a gill arch that contains vessels carrying blood to and from gas exchange surfaces.

• Lateral – line system: A line of sensory receptors along the side of some fishes used to detect water movement.

• Operculum: The cover of a gill chamber of a bony fish.• Swim Bladders: A gas filled sac, usually along the dorsal

body wall of bony fishes. It is an outgrowth of the digestive tract and regulates the buoyancy of a fish.

Vocabulary