Chapter 18 – Fishes Chapter 18 – Fishes

Lionfish (Pterois)

Phylum ChordataPhylum Chordata

• BilateralBilateral

• Notocord Notocord – rod of cartilage, it forms the – rod of cartilage, it forms the spine in some – (2)spine in some – (2)

• Dorsal neural tube Dorsal neural tube – it forms the spinal cord – it forms the spinal cord in some – (3)in some – (3)

• Pharyngeal slits Pharyngeal slits – they become gills, filter – they become gills, filter feeding organs or jaws in some – (10)feeding organs or jaws in some – (10)

• Post anal tail Post anal tail – (4)– (4)

• Endostyle Endostyle – a ventral groove– a ventral groove

Phylum ChordataPhylum ChordataThere are three groups of chordates.There are three groups of chordates.

•Urochordata (“tail cord”):Urochordata (“tail cord”):

tunicates (sea squirts)tunicates (sea squirts)–Sessile filter feedersSessile filter feeders–Motile larvaeMotile larvae–Notochord in their taleNotochord in their tale

•Cephalochordata: lanceletsCephalochordata: lancelets–No brainNo brain–Head and sense organsHead and sense organs

•CraniataCraniata–Have a skullHave a skull

Subphylum VertebrataSubphylum Vertebrata

• Any chordate (Craniate) with a Any chordate (Craniate) with a backbonebackbone– Surrounds the spinal cordSurrounds the spinal cord– provides primary axial supportprovides primary axial support

• Skull that protects the brainSkull that protects the brain

• Includes fish, amphibians, reptiles, Includes fish, amphibians, reptiles, mammals, and birds.mammals, and birds.

• 64,000 species64,000 species

• 4% of all animals are vertebrates.4% of all animals are vertebrates.

Includes the following:Includes the following:–Class Class Agnatha (jawless fishes)(jawless fishes)–Class Class Chondrichthyes (cartilaginous fishes)(cartilaginous fishes)–Class Class Osteichthyes (bony fishes)(bony fishes)

And these we will discuss later:And these we will discuss later:–Class Class Amphibia (amphibians)(amphibians)–Class Class Reptilia (reptiles)(reptiles)–Class Class Aves (birds)(birds)–Class Class Mammalia (mammals)(mammals)

Subphylum VertebrataSubphylum Vertebrata

• Conodont – Conodont – An early Vertebrate An early Vertebrate ancestor, noted for having a pair of ancestor, noted for having a pair of eyes, and muscles on its side that eyes, and muscles on its side that indicate it may have been a indicate it may have been a predatory feeder. It had no jaws and predatory feeder. It had no jaws and no paired appendages (fins).no paired appendages (fins).

Classification of FishesClassification of Fishes• Agnathans –Agnathans – Early fish that lack Early fish that lack

jaws and paired appendages. Their jaws and paired appendages. Their skeleton is cartilaginous. They have skeleton is cartilaginous. They have a notochord or primitive support a notochord or primitive support structure.structure.

Ex. HagfishEx. Hagfish and and LampreyLampreyParasites and scavengers respectively.Parasites and scavengers respectively.

• Gnathastomes –Gnathastomes – Hinged jaws and Hinged jaws and paired fins mark this group. They paired fins mark this group. They have a vertebral column that seems have a vertebral column that seems to have replaced the notochord.to have replaced the notochord.

There are two groups of Gnathastomes There are two groups of Gnathastomes that we will be looking at.that we will be looking at.

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Fig. 18.8

Paired Appendages

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(ventral unpaired)

• Chondrichthyes –Chondrichthyes – Cartilaginous fish Cartilaginous fish lacking a swim bladder or lungs.lacking a swim bladder or lungs.

Ex. Sharks, skates, rays and ratfishes.Ex. Sharks, skates, rays and ratfishes.

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Fig. 18.9a

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Class Chondrichthyes

Photo © Vol. 53/CORBIS

Operculum – Operculum – a gill covering seen in a gill covering seen in some Chondrichthians. Helps pump some Chondrichthians. Helps pump water over gills.water over gills.

• Osteichthyes –Osteichthyes – Fish with a hard Fish with a hard bone skeleton, operculum covering a bone skeleton, operculum covering a single gill opening. They also have single gill opening. They also have lungs or swim bladders. They are lungs or swim bladders. They are sometimes called the “bony fish”. sometimes called the “bony fish”.

LungfishLungfish

LocomotionLocomotion

To beat the resistance that water To beat the resistance that water provides to movement, fish have provides to movement, fish have developed some mechanisms to move.developed some mechanisms to move.

• They use fins to push against the water, They use fins to push against the water, and direct movement, like a rudder on a and direct movement, like a rudder on a boat. They have a muscular body wall boat. They have a muscular body wall they use to propel themselves forward. they use to propel themselves forward. The muscles are in zigzag pattern.The muscles are in zigzag pattern.

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Nutrition and Digestive Nutrition and Digestive SystemSystem• The Agnathans are often parasitic. The Agnathans are often parasitic.

Some fish have gill rakers, or modified Some fish have gill rakers, or modified gills for straining food particles from the gills for straining food particles from the water. Most modern fish are predators water. Most modern fish are predators

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Fig. 18.10

Fr. R. Steale, Sharks of the World, Copyright © 1985 Cassel PLC, London.

Scales and Teeth of Sharks

Circulation and Gas Circulation and Gas ExchangeExchangeFor gas exchange to occur, the fish must have For gas exchange to occur, the fish must have

constant water flow over the gills.constant water flow over the gills.

• Ram Ventilation –Ram Ventilation – by moving with the by moving with the mouth open some fish force water over their mouth open some fish force water over their gills.gills.

– Gill Arches –Gill Arches – The support structures for the gills. The support structures for the gills.– Gill Filaments –Gill Filaments – Two extensions from each gill Two extensions from each gill

arch that provide additional surface area for arch that provide additional surface area for respiration.respiration.

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Circulatory System of FishesFig. 18.15

• Pharyngeal Lamellae –Pharyngeal Lamellae – Folds of Folds of epithelium that are located on the epithelium that are located on the gill filaments.gill filaments.

• Countercurrent Exchange Countercurrent Exchange Mechanism –Mechanism – As blood and water As blood and water move in opposite directions, gases move in opposite directions, gases are exchanged on the gills.are exchanged on the gills.

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Fig. 18.16

Gas Exchange at Pharyngeal Lamellae

Photo (b) © Fred Hossler/VU

• Pneumatic Sacs –Pneumatic Sacs – Gas chambers Gas chambers that fill with air. Some are used for that fill with air. Some are used for gas exchange.gas exchange.

– Swim Bladders –Swim Bladders – Pneumatic sacs that Pneumatic sacs that are used by fish to maintain buoyancy. are used by fish to maintain buoyancy.

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Evolution of Pneumatic SacsFig. 18.17

Nervous and Sensory Nervous and Sensory FunctionsFunctions

• Lateral-line System – Lateral-line System – A row of A row of sensory pits that run along the sides of sensory pits that run along the sides of fish. They detect water currents, fish. They detect water currents, predators, prey and some low predators, prey and some low frequency sounds.frequency sounds.

• Electroreception –Electroreception – Detection of Detection of electrical fields. Some fish are able to electrical fields. Some fish are able to sense the weak electrical emanations of sense the weak electrical emanations of other living things.other living things.

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Fig. 18.18a

Electrical Field of Fish

Excretion and Excretion and OsmoregulationOsmoregulation• Nephrons –Nephrons – Structures in the Structures in the

kidneys that filter nitrogenous kidneys that filter nitrogenous wastes, ions water and small wastes, ions water and small inorganic compounds.inorganic compounds.

• Glomerulus –Glomerulus – The capillaries that The capillaries that move across the nephrons aiding in move across the nephrons aiding in waste removal.waste removal.

• Cloaca –Cloaca – A common opening for A common opening for excretory, digestive and reproductive excretory, digestive and reproductive products.products.

Reproduction and Reproduction and DevelopmentDevelopment

• Oviparous –Oviparous – Most fish have eggs Most fish have eggs that develop outside the female from that develop outside the female from a stored yolk.a stored yolk.

• Ovoviviparous –Ovoviviparous – Some develop Some develop eggs in a modified oviduct in the eggs in a modified oviduct in the female. They use nutrients in the female. They use nutrients in the yolk.yolk.

• Viviparous – Viviparous – Some shark young Some shark young develop inside the female, and gain develop inside the female, and gain their nutrients from the mother.their nutrients from the mother.