Chapter 18 – Fishes Lionfish (Pterois)

Phylum Chordata Bilateral Bilateral Notocord – rod of cartilage, it forms the spine in some – (2) Notocord – rod of cartilage, it forms the spine in some – (2) Dorsal neural tube – it forms the spinal cord in some – (3) Dorsal neural tube – it forms the spinal cord in some – (3) Pharyngeal slits – they become gills, filter feeding organs or jaws in some – (10) Pharyngeal slits – they become gills, filter feeding organs or jaws in some – (10) Post anal tail – (4) Post anal tail – (4) Endostyle – a ventral groove Endostyle – a ventral groove

Phylum Chordata There are three groups of chordates. Urochordata (“tail cord”): Urochordata (“tail cord”): tunicates (sea squirts) –Sessile filter feeders –Motile larvae –Notochord in their tale Cephalochordata: lancelets Cephalochordata: lancelets –No brain –Head and sense organs Craniata Craniata –Have a skull

Subphylum Vertebrata Any chordate (Craniate) with a backbone Any chordate (Craniate) with a backbone –Surrounds the spinal cord –provides primary axial support Skull that protects the brain Skull that protects the brain Includes fish, amphibians, reptiles, mammals, and birds. Includes fish, amphibians, reptiles, mammals, and birds. 64,000 species 64,000 species 4% of all animals are vertebrates. 4% of all animals are vertebrates.

Includes the following: –Class Agnatha (jawless fishes) Agnatha –Class Chondrichthyes (cartilaginous fishes) Chondrichthyes –Class Osteichthyes (bony fishes) Osteichthyes And these we will discuss later: –Class Amphibia (amphibians) Amphibia –Class Reptilia (reptiles) Reptilia –Class Aves (birds) Aves –Class Mammalia (mammals) Mammalia Subphylum Vertebrata

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

Classification of Fishes Agnathans – Early fish that lack jaws and paired appendages. Their skeleton is cartilaginous. They have a notochord or primitive support structure. Agnathans – Early fish that lack jaws and paired appendages. Their skeleton is cartilaginous. They have a notochord or primitive support structure. Ex. Hagfish and Lamprey Parasites and scavengers respectively.

Gnathastomes – Hinged jaws and paired fins mark this group. They have a vertebral column that seems to have replaced the notochord. Gnathastomes – Hinged jaws and paired fins mark this group. They have a vertebral column that seems to have replaced the notochord. There are two groups of Gnathastomes that we will be looking at.

18-6 Fig Paired Appendages Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (ventral unpaired)

Chondrichthyes – Cartilaginous fish lacking a swim bladder or lungs. Chondrichthyes – Cartilaginous fish lacking a swim bladder or lungs. Ex. Sharks, skates, rays and ratfishes.

18-7 Fig. 18.9a Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Chondrichthyes Photo © Vol. 53/CORBIS

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

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

Lungfish

Locomotion To beat the resistance that water provides to movement, fish have developed some mechanisms to move. They use fins to push against the water, and direct movement, like a rudder on a boat. They have a muscular body wall they use to propel themselves forward. The muscles are in zigzag pattern. They use fins to push against the water, and direct movement, like a rudder on a boat. They have a muscular body wall they use to propel themselves forward. The muscles are in zigzag pattern.^^^^^^

Nutrition and Digestive System The Agnathans are often parasitic. Some fish have gill rakers, or modified gills for straining food particles from the water. Most modern fish are predators The Agnathans are often parasitic. Some fish have gill rakers, or modified gills for straining food particles from the water. Most modern fish are predators

18-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig Fr. R. Steale, Sharks of the World, Copyright © 1985 Cassel PLC, London. Scales and Teeth of Sharks

Circulation and Gas Exchange For gas exchange to occur, the fish must have constant water flow over the gills. Ram Ventilation – by moving with the mouth open some fish force water over their gills. Ram Ventilation – by moving with the mouth open some fish force water over their gills. –Gill Arches – The support structures for the gills. –Gill Filaments – Two extensions from each gill arch that provide additional surface area for respiration.

18-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Circulatory System of Fishes Fig

Pharyngeal Lamellae – Folds of epithelium that are located on the gill filaments. Pharyngeal Lamellae – Folds of epithelium that are located on the gill filaments. Countercurrent Exchange Mechanism – As blood and water move in opposite directions, gases are exchanged on the gills. Countercurrent Exchange Mechanism – As blood and water move in opposite directions, gases are exchanged on the gills.

18-12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig Gas Exchange at Pharyngeal Lamellae Photo (b) © Fred Hossler/VU

Pneumatic Sacs – Gas chambers that fill with air. Some are used for gas exchange. Pneumatic Sacs – Gas chambers that fill with air. Some are used for gas exchange. –Swim Bladders – Pneumatic sacs that are used by fish to maintain buoyancy.

18-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Evolution of Pneumatic Sacs Fig

Nervous and Sensory Functions Lateral-line System – A row of sensory pits that run along the sides of fish. They detect water currents, predators, prey and some low frequency sounds. Lateral-line System – A row of sensory pits that run along the sides of fish. They detect water currents, predators, prey and some low frequency sounds. Electroreception – Detection of electrical fields. Some fish are able to sense the weak electrical emanations of other living things. Electroreception – Detection of electrical fields. Some fish are able to sense the weak electrical emanations of other living things.

18-14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig a Electrical Field of Fish

Excretion and Osmoregulation Nephrons – Structures in the kidneys that filter nitrogenous wastes, ions water and small inorganic compounds. Nephrons – Structures in the kidneys that filter nitrogenous wastes, ions water and small inorganic compounds. Glomerulus – The capillaries that move across the nephrons aiding in waste removal. Glomerulus – The capillaries that move across the nephrons aiding in waste removal. Cloaca – A common opening for excretory, digestive and reproductive products. Cloaca – A common opening for excretory, digestive and reproductive products.

Reproduction and Development Oviparous – Most fish have eggs that develop outside the female from a stored yolk. Oviparous – Most fish have eggs that develop outside the female from a stored yolk. Ovoviviparous – Some develop eggs in a modified oviduct in the female. They use nutrients in the yolk. Ovoviviparous – Some develop eggs in a modified oviduct in the female. They use nutrients in the yolk. Viviparous – Some shark young develop inside the female, and gain their nutrients from the mother. Viviparous – Some shark young develop inside the female, and gain their nutrients from the mother.