Characteristics of all Fish • All fish are aquatic • All fish are vertebrates • All fish have gills • All fish have appendages in the form of fins • Most fish have skin with scales
Different Groups of Fishes • There are three main groups of fish. • The jawless fishes are called the Agnathans. • The cartilaginous fishes are called the Chondrichthyes. • The bony fishes are called Osteichthyes. • The bony fishes are also subdivided into the ray-finned fishes called Actinopterygii and the lobe-finned fishes called Sarcopterygii.
The Agnathans (Jawless Fish) • Agnathans have a slender, eel-like body. • Agnathans have naked skin, no scales. • Agnathans have median fins only, no paired fins like the pelvic or pectoral fins. • Agnathans have a cartilaginous skeleton and a notochord, but a reduced or absent vertebrae. • Agnathans lack jaws, but they have mouths that are adapted to parasitism or scavenging.
The Agnathans • One class of Agnathans is called Myxini • The types of fish that are found in the class Myxini are called hagfishes. • Hagfish are a marine fish that feed on dead or dying animals like fish, annelids, molluscs,crustaceans and marine mammals. • Most hagfish are scavengers. They are almost completely blind, but they have an acute sense of smell. They are attracted to dead flesh.
The Agnathans • The hagfish attach to their food with their teeth and they tear off pieces of flesh with their rasp-like tongue. In order to achieve more leverage they can form a knot in their body and push the knot in their body against the body of their prey. • Hagfish are also well known for their unique ability to produce enormous amounts of slime. • Another class of Agnathans is called class Cephalaspidomorphi. Fish in this class of Agnathans are called lampreys.
The Agnathans • Most lampreys are ectoparasitic and attach to the skin and feed on the blood of their host. • In North America, marine and freshwater lampreys spawn in the winter or spring in shallow gravel and sand in freshwater streams. • Adults die soon after spawning, then the eggs hatch in approximately 2 weeks, and small larvae hatch called ammocoetes.
The Agnathans • The ammocoetes feed on small invertebrates. • After the ammocoetes metamorphose into adults, they migrate to the seaor stay in the freshwater streams and attach to a fish host with their teeth and suck their blood. • To promote the flow of blood, lampreys inject an anticoagulant into the wound. • Lamprey eels were an invasive species to the Great Lakes region in the 1950's and they almost completely decimated the lake trout fishery.
Class Chondrichthyes (Cartilaginous Fishes) • Chondrichthyes have a cartilaginous skeleton. • Chondrichthyes have placoid scales, which are anatomically similar to their teeth. • Chondrichthyes have a j-shaped stomach with a spiral-valved intestine. • Chondrichthyes have exposed gill slits with no protective covering called an operculum. • Chondrichthyes do not have a swim bladder. • For buoyancy they have an oily liver filled with squalene. • Most Chondrichthyes exhibit internal fertilization.
Subclass Elasmobranchii (Sharks and Rays) • About half (45%) of elasmobranchs are sharks. • Sharks are typically predaceous fish with five to seven pairs of gills and gill slits. • Sharks have a spiracle or opening behind each eye that is used to bring water to the gills. • Sharks are heavier than water, so they must continue to swim forward or they will sink. • Sharks vary is size from the harmless plankton-eating whale shark (15 meters), to the spiny dogfish sharks that rarely exceed 1 meter.
Subclass Elasmobranchii • Sharks have an assymetricalheterocercal tail. • The heterocercal tail provides lift and thrust. • The broad head and pectoral fins also provide lift in the water. • The placoid scales of the shark reduce turbulence. The teeth of the shark resemble the placoid scales and are replaceable. • The placoid scales are made of a dentine and enamel-like substance just like teeth.
Subclass Elasmobranchii • Sharks have an extremely good sense of smell and a system of canals on the sides of the body that can detect vibrations called a lateral line. • At close range, the shark relies on its vision and special sensory receptors called the ampullary organs of Lorenzini to detect their prey. • The ampullary organs of Lorenzini can detect bioelectric fields that surround all animals. • Male sharks have a clasper on their pelvic fins that transfers sperm internally to the female.
Subclass Elasmobranchii • Many sharks and skates are oviparous, meaning they lay eggs soon after fertilization. • Most sharks are ovoviviparous, meaning fertilization is internal, eggs are developed, but they are hatched internally and the young receive nourishment via a yolk sac rather than a placenta. Developed young are born live. • Some sharks are viviparous, meaning the young are not in an egg but a placenta, and the young are born live after development.
Subclass Elasmobranchii • Over half of the elasmobranchs are rays. • Rays are a group of fish that includes skates, stingrays, electric rays and manta rays. • Rays have a dorsoventrally flattened bodies and enlarged pectoral fins, which they move in a wave-like motion to swim through the water. • Rays have large spiracles on top of their head because they often bury their mouth in the sand while hunting. This prevents clogging of the gills with sand and debris while hunting.
6'' stingray tail barb Subclass Elasmobranchii • Stingrays have a long, slender, whiplike tail that is armed with saw-toothed spines that can inflict dangerous wounds. • Electric rays have muscles on the side of their head that can produce powerful electrical fields that can shock and stun their prey.
The Bony Fishes (Osteichthyes) • Bony fish have a skeleton made of bone. • Most bony fish have a homocercal tail. • Most scales of bony fish are cycloid or ctenoid, occasionallyganoid (like in the gar). • Bony fish have a hard protective covering over the gills called the operculum. • Bony fish have a swim bladder that allows them to achieve neutral buoyancy.
The Bony Fish (Osteichthyes) • There are two classes of bony fish; the ray-finned fishes (Actinopterygii), and the lobe-finned fishes (Sarcopterygii). • One advantage of the bony fishes is having the operculum, which not only protects the gills, but increases efficiency by allowing the fish to actively pump water across the gills. • some bony fishes can use for their swim bladder and their gills for respiration.
The Ray-Finned Fishes (Class Actinopterygii) • The ray-finned fishes have spiny rays in their fins that help them control their movement. • Within the ray-finned fishes there are three different groups of fishes; the chondrosteans, the holosteans, and the teleosts. • The chondrosteans are a rare group of fish that are mostly extinct and found in the fossil record. • They have a partial cartilaginous and bony skeleton. • Some also have a heterocercal tail and spiracles. • Some examples of extant (living) chondrosteans include sturgeons, bichir (pronounced bee-SHEER), and the paddlefish.
The Ray-Finned Fishes (Class Actinopterygii) • The next group of ray-finned fishes called the holosteans is also more common in the fossil record than in species alive today. • Bowfins and gars are extant (living) holostean fish. • One common characteristic of the holostean fish is the presence of ganoid scales. • Ganoid scales are hard diamond-shaped scales made of a hard substance called ganoin.
The Ray-Finned Fishes (Class Actinopterygii) • The last group of fish in class Actinopterygii is called the teleosts. Modern bony fish. • Teleosts are the most abundant and diverse group of fish. They make up 96% of all living fish, and almost half of all the vertebrates. • Their scales are lightweight, thin, and flexible, and they are arranged in overlapping layers. • The two most common types of scales of the teleosts are cycloid scales and ctenoid scales.
The Ray-Finned Fishes (Class Actinopterygii) • Most of the bony fishes (teleosts) have a homocercal tail. The homocercal tail allows for more thrust and bursts of speed. • Some of the features of the teleosts fish such as lightweight and flexible scales, and a homocercal tail that provides more thrust, have made the teleosts one of the most successful group of fish and vertebrates in the world.
The Lobe-Finned Fishes (Class Sarcopterygii) • The Lobe-Finned fishes (class Sarcopterygii) have fleshy lobes or appendages which allow them to move around in the shallow water. • Lobe-finned fishes also have a diphycercal tail, which is not very efficient for moving fast. • The coelacanth and lungfishes are examples of lobe-finned fish in the class Sarcopterygii. • There are only 6 living species of lungfish and 2 known living species of coelacanth.
The Lobe-Finned Fishes (Class Sarcopterygii) • The Australian lungfish can survive in hot, stagnant, oxygen-poor waters by coming to the surface and gulping air into its swim bladder. • The South American and African lungfish can live out of water for long periods of time. • During the dry season, the African lungfish secretes large amounts of slime that mix with the mud to form a hard cocoon. It remains dormant in the cocoon until after it rains.
The Lobe-Finned Fishes (Class Sarcopterygii) • Coelacanths were once believed to be a fish that was extinct for 70 million years. • In 1938, a fishing trawl caught the remains of a coelacanth off the coast of South Africa. • An intensive search began and scientists were successful at catching live specimens. • In 1998, a new species of coelacanth was discovered in Indonesia, 5,000 miles away. • The eggs of the coelacanth are unusually large (9 cm). They hatch fully formed from the egg.
Locomotion in Water • The muscle structure of fish is composed of zig zag or sideways, W-shapedmyomeres. • The unique arrangement of the myomeres allows for more power and control. • More surface area on the head and tail (more forward motion), and less surface area on the caudal pedunclereduces resistance in the water, and increases a fishes swimming efficiency. • Fast moving fish like the tuna, marlin, swordfish, and wahoo all have a narrow caudal peduncle and sickle-shaped tail.
Neutral Buoyancy • All fishes are slightly heavier than water. • To keep from sinking, sharks have to keep moving and they have a heterocercal tail. • Sharks also have a very large liver filled with an oily substance known as squalene. • Squalene is less dense than water (0.86 g/mL) and helps the shark to not sink. • Bony fish use a gas-filled swim bladder to achieve neutral buoyancy.
Respiration • Gills in bony fish have a protective operculum and four gill arches. • Gill rakers project forward on the gill arches and strain out food and debris. • Gill filaments project back from the gill arches. • Gill filaments are made up of fine platelike structures called lamellae. • The lamellae are richly supplied with blood vessels (capillaries).
Respiration • The blood vessels in the lamellae run in the opposite direction that water flows over the gills. • This is a remarkable adaptation of fishes that allows up to 85% or more oxygen saturation. • This method is called countercurrent flow. • If the blood flowed in the same direction as the water flowed over the gills, the maximum amount of oxygen saturation could never be more than 50%.
Osmoregulation • Freshwater fish are hyperosmotic regulators, because they live in an environment with low concentrations of salt. Salt-absorbing cells in their gills actively pump salt into their bodies and their kidneys produce dilute urine. • Marine fish are hypoosmotic regulators, because they live in an environment with a high concentration of salt. Salt-secretory cells in their gills actively pump salt out of their bodies and their kidneys produce concentrated urine.