Chapter 16 Notes, 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

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 mammalscrustaceans 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 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.

AGNATHANS (JAWLESS FISH)

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.

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 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 operculum (protective gill plate that covers the gills).

Chondrichthyes do not have a swim bladder.

For buoyancy they have an oily liver filled with squalene.

Most Chondrichthyes exhibit internal fertilization.

PLACOID SCALES AND EXTERNAL GILL SLITS

SUBCLASS ELASMOBRANCHII (SHARKS AND RAYS)

About half of elasmobranchs are sharks. Sharks are typically predators with 5-7 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 assymetrical heterocercal tail.

The heterocercal tail provides lift and thrust.

The broad head and pectoral fins also help 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 dentine and enamel, just like teeth.

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 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.

AMPULLARY ORGANS OF LORENZINI

SUBCLASS ELASMOBRANCHII Many sharks and skates are oviparous,

meaning they lay eggs after fertilization. Most sharks are ovoviviparous, meaning

fertilization is internal, eggs are developed and hatched internally. 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.

SHARK CLASPERS

SUBCLASS ELASMOBRANCHII About 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.

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.

6'' stingray tail barb

STINGRAYS

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, occasionally ganoid (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.

SCALES TYPES

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 their swim bladder and their gills for respiration.

THE OPERCULUM

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 subgroups of fishes; 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

MONSTER STURGEON FROM THE FRAZER RIVER IN BRITISH COLUMBIA, CANADA


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.

HOLOSTEANS (GAR AND BOWFIN)

GANOID SCALES AND ALLIGATOR GAR


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.


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 such as lightweight and flexible scales, and a homocercal tail provides speed.

These characteristics have made the teleosts some of the most successful groups 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 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.

LUNGFISH


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 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 in Indonesia, 5,000 miles away.

The eggs of the coelacanth are unusually large (9 cm). They hatch fully formed from the egg.

COELACANTH

LOCOMOTION IN WATER The muscle structure of fish is composed of zig

zag or sideways, w-shaped myomeres. 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 peduncle reduces 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.

TAIL SHAPE OF A FAST MOVING FISH

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).

ANATOMY OF THE GILLS

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%.

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-secretory 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 (6-10 years) in freshwater, and migrate to the ocean where they spawn.

After the young of the eel hatch, they are in the form of leaf-shaped larva called leptocephali.

AMERICAN EEL LIFE CYCLE AND MIGRATION

MIGRATION The leptocephali of the eels begin a long

migration back to their home streams. After about a year, they develop into juvenile eels called elvers. The elvers then migrate back upstream and develop into adult eels.

Migrating Salmon do the opposite. Salmon are anadromous, meaning they spend

most of their adult lives at sea, and migrate to freshwater to spawn.

MIGRATION The Atlantic salmon and the steelhead can

make multiple spawning trips. Pacific salmon all die after they have spawned only once.

Salmon have a remarkable homing instinct. The smolt of the red (sockeye) salmon, migrate

downstream to the ocean. Once there, they spend nearly four years in the ocean wandering hundreds of miles.

Then, they almost always return to the exact stream where they were born.

MIGRATION Occasionally adult salmon stray from stream to

stream to allow mixing of the gene pool. Scientific studies have shown that what allows

salmon to do this is an imprinting of the distinct odor of the stream where they were born.

It is believed that the odors that they smell is a combination of compounds released by the surrounding vegetation and soil of the stream.

They also imprint the streams downriver where they were born to create a map to get home.

PACIFIC SALMON LIFE CYCLE

REPRODUCTION

We already discussed reproduction in 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 strategy of most bony fish in reproduction is to produce as many eggs as possible because the mortality rate is high.

REPRODUCTION Many pelagic (open ocean) fish release their eggs

directly into the open water. Their eggs are buoyant and float with the ocean currents.

Many near shore and benthic (bottom dwelling) fish release eggs that are nonbuoyant and adhesive, so they will stick to the bottom substrate in order to prevent them from drifting away.

After eggs are released and fertilized, the egg eventually hatches and an alevin hatches.

Alevin have a yolk sac to provide nourishment.

EGGS AND ALEVIN

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Chapter 16 Notes, Fish