Chapter 16 Notes Fish CHARACTERISTICS OF ALL FISH

Chapter 16 Notes, Fish

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

TAXONOMY OF FISH There are three main taxons of fish. The jawless fishes are called the Agnathans. The cartilaginous fishes are called the Chondrichthyes. The bony fishes are called Osteichthyes.

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 (notochord), but vertebrae are absent. Agnathans lack jaws, but they have mouths that are adapted for parasitism or scavenging.

LAMPREY ANATOMY

THE AGNATHANS One class of Agnathans is called class Myxini The types of fish that are found in the class Myxini are called hagfishes. Hagfish are a marine fish that feeds 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.

HAGFISH

THE AGNATHANS The hagfish attach to their food with their teeth and they tear off pieces of flesh with their rasplike tongue. In order to achieve more leverage they form a knot in their body and push the knot in their body against their food (dead flesh). Hagfish are also well known for their unique ability to produce large amounts of slime. Another class of Agnathans is called class Cephalaspidomorphi. Fish in this class of Agnathans are called lampreys.

AGNATHANS (JAWLESS FISH)

THE AGNATHANS Most lampreys are ectoparasites that attach to the skin of a fish (host) and feed on the blood. In North America, marine and freshwater lampreys spawn in winter or spring in shallow gravel or sand in freshwater streams. Adults die soon after spawning, then the eggs hatch in approximately 2 weeks, and produce small larvae called ammocoetes.

LAMPREYS ON A LAKE TROUT

THE AGNATHANS The ammocoetes feed on small invertebrates. After the ammocoetes metamorphose into adults, they migrate to the sea or 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.

AMMOCOETES (LAMPREY LARVA)

CLASS CHONDRICHTHYES (CARTILAGINOUS FISH) Chondrichthyes fish have a cartilaginous skeleton. Chondrichthyes fish have placoid scales, which are similar in shape and composition to their teeth. Chondrichthyes fish have a j-shaped stomach and a spiral -valved intestine. Chondrichthyes fish have exposed gill slits with no operculum (protective gill plate that covers the gills). Chondrichthyes fish do not have a swim bladder. For buoyancy they have an oily liver filled with a lowdensity substance called squalene. Most Chondrichthyes fish reproduce by way of internal fertilization.

PLACOID SCALES AND EXTERNAL GILL SLITS

CLASS CHONDRICHTHYES AND SUBCLASS ELASMOBRANCHII (SHARKS AND RAYS) Most fish in the class Chondrichthyes are in the subclass Elasmobranchii and about half of the members of this subclass are sharks. Sharks typically are predators with 5 -7 pairs of gills and external gill slits. Sharks have a spiracle behind each eye that is used to bring more water into the gills. Sharks are heavier than water, so they must continue to swim forward or they will sink.

SHARK ANATOMY

SUBCLASS ELASMOBRANCHII Sharks have an assymetrical heterocercal tail. The heterocercal tail provides lift and thrust. The broad head and pectoral fins also help to provide lift in the water. The placoid scales of the shark reduce turbulence. The teeth of a shark resemble the placoid scales and the teeth are replaceable. The placoid scales, like teeth, are made of dentine and enamel.

HETEROCERCAL TAIL OF A SHARK

SUBCLASS ELASMOBRANCHII Sharks have an extremely good sense of smell and a system of canals on the sides of the body, called a lateral line, that can detect vibrations. At close range, the shark relies on vision and special sensory receptors, called the ampullary organs of Lorenzini to help detect their prey. The ampullary organs of Lorenzini can detect bioelectric fields that surround all animals. Male sharks have claspers on their pelvic fins that transfer sperm internally to the female.

AMPULLARY ORGANS OF LORENZINI

SUBCLASS ELASMOBRANCHII Some sharks and skates are oviparous, and lay their eggs after fertilization. Some sharks are viviparous, meaning the young are not in an egg, but a placenta, and the young are born live after development. But most sharks are ovoviviparous, meaning fertilization is internal, eggs are developed and hatched internally. The young receive nourishment from a yolk sac rather than a placenta. Young are born live.

SHARK CLASPERS

SUBCLASS ELASMOBRANCHII The other half of elasmobranchii fish are rays. Rays are a group of fish that includes skates, stingrays, electric rays and manta rays. Rays have dorsoventrally flattened bodies and enlarged pectoral fins, which they move in a wave-like motion to swim. 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 debris while hunting.

SUBCLASS ELASMOBRANCHII 6'' stingray tail barb Stingrays have a long, slender, whip-like tail that is armed with saw-toothed spines and can inflict serious wounds. Electric rays have muscles on the side of their head that can produce powerful electrical fields in order to shock and stun their prey.

STINGRAYS

THE BONY FISHES (OSTEICHTHYES) Bony fish have a skeleton made of bone. Most bony fish have a homocercal tail. Scales of bony fish are either cycloid , ctenoid, or occasionally ganoid (like 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.

SCALES TYPES

THE BONY FISH (OSTEICHTHYES) There are two main subclasses of bony fish; the ray-finned fishes (Actinopterygii), and the lobefinned fishes (Sarcopterygii). One advantage of the bony fishes, is they have an operculum, which not only protects the gills, but also increases efficiency by allowing the fish to actively pump water across the gills. some bony fishes can use other organs, like the swim bladder in combination with their gills to aid them in respiration.

THE OPERCULUM

THE RAY-FINNED FISHES (SUBCLASS ACTINOPTERYGII) The ray-finned fishes have spiny rays in their fins that help control their movement. Within the ray-finned fishes there are three different smaller groups or taxons of fish; the chondrosteans, the holosteans, and the teleosts. The chondrosteans are a rare group of fish that are mostly extinct and mostly 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.

CHONDROSTEANS

LARGE STURGEON FROM THE FRAZER RIVER IN BRITISH COLUMBIA, CANADA

COLUMBIA RIVER STURGEON

THE RAY-FINNED FISHES (SUBCLASS ACTINOPTERYGII) The next group of ray-finned fishes, called the holosteans are 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, bone-like substance called ganoin.

HOLOSTEANS (GAR AND BOWFIN)

GANOID SCALES AND ALLIGATOR GAR

THE RAY-FINNED FISHES (SUBCLASS ACTINOPTERYGII) The last group of fish in the subclass Actinopterygii are called the teleosts. Teleosts are the most abundant and diverse group of fish. They make up 96% of all living fish, and about 50% of all the vertebrates. Their scales are thin, lightweight, 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 (SUBCLASS ACTINOPTERYGII) Most of the teleosts have a homocercal tail. The homocercal tail allows for more thrust and rapid bursts of speed. These unique features of the teleosts, such as the presence of lightweight flexible scales, a homocercal tail, a swim bladder and an operculum, have made the teleosts become the most successful group of fish and vertebrates in the world.

THE LOBE-FINNED FISHES (SUBCLASS SARCOPTERYGII) The Lobe-Finned fishes (subclass Sarcopterygii) have fleshy lobes or appendages which allow them to move around in the shallow water. Lobe-finned fishes have a diphycercal tail, which is not very efficient for swimming fast. More useful for crawling through shallow water. The coelacanth and lungfishes are examples of lobe-finned fish in the subclass Sarcopterygii. There are only 6 living species of lungfish and only 2 known living species of coelacanth.

THE LOBE-FINNED FISHES (SUBCLASS 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 burrow in the mud in a drought and live without water for several weeks or months at a time. During the dry season, the African lungfish secretes large amounts of slime that mixes with mud to form a hard cocoon. It remains dormant in the cocoon until after it rains.

AFRICAN LUNGFISH IN COCOON

LUNGFISH

THE LOBE-FINNED FISHES (CLASS SARCOPTERYGII) Coelacanths were once believed by some to be a fish that was extinct for 70 million years. In 1938, a fishing trawler caught the remains of a coelacanth off the coast of South Africa by the island of Madagascar. An intensive search began and scientists were successful at catching some live specimens. In 1998, a new species of coelacanth was discovered 5, 000 miles away, in Indonesia. The eggs of the coelacanth are unusually large for a fish (9 cm). They hatch fully formed from the egg.

COELACANTH

LOCOMOTION IN WATER The muscles of fish are composed of zig-zag, wshaped muscle fibers called myomeres. The unique arrangement of the myomeres allow for more power and control. Fast moving fish like the tuna, marlin, swordfish, and wahoo all have broad bodies, narrow caudal peduncles, and sickle-shaped tails. More surface area on the head and tail, and less surface area on the caudal peduncle. This reduces resistance in the water, and increases a fishes swimming efficiency.

MYOMERES

TAIL AND BODY SHAPE OF A FAST MOVING FISH LIKE A MARLIN

RESPIRATION Gills in bony fish have a protective operculum and four gill arches that support the gills. 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, delicate plate -like structures called lamellae. The lamellae are richly supplied with blood vessels (capillaries).

ANATOMY OF THE GILLS

RESPIRATION The blood vessels in the lamellae run in the opposite direction that water flows over the gills. This is an adaptation of fish that allows up to 85% or more oxygen saturation. This adaptation is called countercurrent flow. If blood flowed in the same direction as water, the maximum amount of oxygen saturation could never be more than 50%.

COUNTERCURRENT FLOW

HOW COUNTERCURRENT FLOW WORKS

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-secreting cells in their gills actively pump salt out of their bodies and their kidneys produce concentrated urine.

OSMOREGULATION

MIGRATION Some fish spend a period of their life in both fresh and salt water. This type of migratory behavior is called being diadromous. Some fish like freshwater eels, are catadromous, meaning they spend most of their adult life in freshwater, and migrate to the ocean where they spawn. After the young eel hatch, they are in the form of leaf-shaped larva called leptocephali.

MIGRATION The leptocephali of the eels begin a long migration to freshwater streams. After about a year, they develop into juvenile eels called elvers. The elvers eventually mature and develop into adult eels, which will eventually return to the ocean to spawn in about 6 -15 years. Salmon are anadromous, meaning they spend most of their adult lives at sea, and migrate to freshwater to spawn.

FRESHWATER (AMERICAN AND EUROPEAN) EEL LIFE CYCLE AND MIGRATION

MIGRATION The Atlantic salmon and steelhead are interoparous, meaning they can spawn multiple times. Pacific salmon are semelparous, meaning they die after they have spawned only once. Salmon have a remarkable homing instinct. The smolt of the salmon, migrate downstream to the ocean. Once there, they spend 3 -5 years in the ocean wandering hundreds of miles. Then, they almost always return to the exact same stream where they were born.

MIGRATION Occasionally some salmon stray from stream to allow mixing of the gene pool. Studies have shown that what allows salmon to find their own stream is they imprint the distinct odor of the stream where they were born. It is believed that the odors they smell are a combination of compounds released by the surrounding vegetation and soil of the stream. They also imprint the streams downriver from where they were born to create a mental map.

PACIFIC SALMON LIFE CYCLE

REPRODUCTION We already discussed reproduction in the Elasmobranchs (Sharks and Rays). Bony fish are almost all oviparous, which means they lay and fertilize their eggs externally and the young develop externally. There are some examples of ovoviviparous bony fish like mollies and guppies. The reproductive strategy of most bony fish is to produce as many eggs as possible because the mortality rate is high.

REPRODUCTION Many pelagic fish like halibut, release their eggs directly into the open water. Their eggs are buoyant and float with the ocean currents. Many freshwater, near shore, and benthic fish release eggs that are non-buoyant and adhesive, so the eggs will stick to the bottom substrate in order to prevent them from drifting away. After eggs are released and fertilized, the eggs eventually hatch into alevin. Alevin are the developing embryos of fish that have a yolk sac that provides nourishment.

EGGS AND ALEVIN