About the pagination of this eBook Due to the unique page numbering scheme of this book, the electronic pagination of the eBook does not match the pagination of the printed version. To navigate the text, please use the electronic Table of Contents that appears alongside the eBook or the Search function. For citation purposes, use the page numbers that appear in the text. FFIISSHH AANNDD AAMMPPHHIIBBIIAANNSS BBrriittaannnniiccaa IIlllluussttrraatteedd SScciieennccee LLiibbrraarryy Encyclopædia Britannica, Inc. Chicago ■ London ■ New Delhi ■ Paris ■ Seoul ■ Sydney ■ Taipei ■ Tokyo BBrriittaannnniiccaa IIlllluussttrraatteedd SScciieennccee LLiibbrraarryy © 2008 Editorial Sol 90 All rights reserved. Idea and Concept of This Work: Editorial Sol 90 Project Management: Fabián Cassan Photo Credits: Corbis, ESA, Getty Images, Graphic News, NASA, National Geographic, Science Photo Library Illustrators: Guido Arroyo, Pablo Aschei, Gustavo J. Caironi, Hernán Cañellas, Leonardo César, José Luis Corsetti, Vanina Farías, Manrique Fernández Buente, Joana Garrido, Celina Hilbert, Jorge Ivanovich, Isidro López, Diego Martín, Jorge Martínez, Marco Menco, Marcelo Morán, Ala de Mosca, Diego Mourelos, Pablo Palastro, Eduardo Pérez, Javier Pérez, Ariel Piroyansky, Fernando Ramallo, Ariel Roldán, Marcel Socías, Néstor Taylor, Trebol Animation, Juan Venegas, Constanza Vicco, Coralia Vignau, Gustavo Yamin, 3DN, 3DOM studio Composition and Pre-press Services: Editorial Sol 90 Translation Services and Index: Publication Services, Inc. Portions © 2008 Encyclopædia Britannica, Inc. Encyclopædia Britannica, Britannica, and the thistle logo are registered trademarks of Encyclopædia Britannica, Inc. Britannica Illustrated Science Library Staff Encyclopædia Britannica, Inc. Editorial Jacob E. Safra, Chairman of the Board Michael Levy, Executive Editor, Core Editorial John Rafferty, Associate Editor, Earth Sciences Jorge Aguilar-Cauz, President William L. Hosch, Associate Editor, Mathematics and Computers Michael Ross, Senior Vice President, Corporate Development Kara Rogers, Associate Editor, Life Sciences Rob Curley, Senior Editor, Science and Technology Dale H. Hoiberg, Senior Vice President and Editor David Hayes, Special Projects Editor Marsha Mackenzie, Director of Production Art and Composition Steven N. Kapusta, Director Carol A. Gaines, Composition Supervisor Christine McCabe, Senior Illustrator International Standard Book Number (set): 978-1-59339-797-5 Media Acquisition International Standard Book Number (volume): Kathy Nakamura, Manager 978-1-59339-805-7 Britannica Illustrated Science Library: Copy Department Fish and Amphibians 2008 Sylvia Wallace, Director Julian Ronning, Supervisor Printed in China Information Management and Retrieval Sheila Vasich, Information Architect Production Control Marilyn L. Barton Manufacturing Kim Gerber, Director www.britannica.com Fish and Amphibians Contents General Characteristics Page 6 Life in the Water Page 18 Diversity Page 38 Amphibians Page 60 People, Fish, and Amphibians Page 80 Water, the VIETNAM Along this country's nearly been in a state of crisis. In Nha Trang Bay this reason, they have developed various 200 miles (300 km) of the growth of outside investment in survival techniques to live in such a wide coastline live great numbers of people who Source of Life aquaculture has limited the economic variety of places. depend on fishing and opportunities of the local population, coral reefs for their livelihood. including fishing for squid and other species in the reefs with hook and line. D T In other cases, commercial fishing espite the fact that lunglike sacs he life of marine creatures is endangers the future of those who rely on evolved because of the difficulty of fascinating and has always been traditional fishing methods to make a breathing with gills in water with low closely linked to human life. This is so living. This is only one of the topics oxygen content, the development of these particularly because fishing has been the explored in this book, which also relates in sacs was also the first step toward moving livelihood of islanders through the years. detail many secrets of these vertebrates, onto land. Some descendants of the first fish Yet for some time, in many areas of the which were among the first creatures with with fleshy, jointed fins, known as lobe-fin world—such as Nha Trang Bay, on the skeletons to appear on the Earth. Perhaps fishes, began to find terrestrial food sources south coast of Vietnam—this activity has knowing more about their habits and and, with time, adapted more completely to modes of life may move us to care for life on the planet's surface. This evolutionary them and protect them. They are at the change—passing from an aquatic to a mercy of variations in water conditions to terrestrial medium—constituted a true a greater extent than humans. revolution for the life-forms that existed up until then. The amphibians we will show you in this book that are living today are a tiny representation of all those that appeared H umans have marveled for centuries at during the Devonian Period, most of which the fact that, after journeying across became extinct during the Triassic Period. the ocean, salmon can find the river where they were born. Is this navigational ability related to the Earth's magnetic field, A sense of smell, instinct, or something else mphibians, especially some frog that humans cannot even imagine? For those species, have become true specialists interested in statistics, in the Yukon River in in the art of mimicry. One of the most Alaska and in Canada, certain tagged fascinating examples is the European tree Chinook salmon covered nearly 2,000 miles frog, which changes color to regulate its (3,200 km) in 60 days. Upon entering the body temperature. On warm, dry evenings river, the salmon stop eating and utilize the the frog rests in sunny places, and its skin is fat they accumulated while in the ocean. pale. As its surroundings become cooler, the After laying their eggs, many of the frog darkens to absorb heat. Although females die. Most ocean fish seek shallow, amphibians are masters of camouflage, nutrient-rich waters in which to lay their which protects them from predators, at eggs. That is why coastal waters and present they are the object of worldwide estuaries are so important to the life cycle of concern because of the dramatic decline in many species. Another oddity of these their populations. Turn the page, and you will animals is that they have adapted to living in discover much more about the abilities of a variety of aquatic habitats: rivers, lakes, fish and amphibians, extraordinary creatures estuaries, coral reefs, and the open sea. For that live right next to us. General Characteristics CROCODILE FISH FIN EARLIEST FORMS 8-9 CARTILAGINOUS FISH 14-15 This fish, which lives in DISTINGUISHING FEATURES 10-11 ANATOMY 16-17 waters with abundant coral reefs, can grow up to 21 BONY FISH 12-13 inches (54 cm) long. F ish were the first vertebrates fish, the earliest fish had no scales, fins, water and salt water. Their bodies are these complex creatures normally with bony skeletons to appear or jawbone, but they did have a type of generally streamlined, being covered breathe through gills that capture on the Earth. They doubtless dorsal fin. Over time they have been with smooth scales and having fins that oxygen dissolved in the water, and they form the most numerous group changing in form and size to adapt to enable them to move with energy, are cold-blooded. of vertebrates. Unlike today's different environments, in both fresh direction, and stability. In place of lungs, 8 GENERAL CHARACTERISTICS FISH AND AMPHIBIANS 9 Earliest Forms Dunkleosteus Dorsal Its head was A The Arthrodira—with a jointed protected by fin The tail was not bout 470 million years ago, the first fish appeared. Unlike today's neck—were armored fish that strong armor. protected by STREAMLINED SHAPE predominated in the late Devonian scales. fish, they did not have a jawbone, fins, or scales. Hard plates The shape of Pteraspis Period. The Devonian predator covered the front part of the fish and formed a protective shield. shows that it was an Dunkleosteus was an arthrodiran excellent swimmer. placoderm that lived over 300 million They also had a solid, flexible dorsal spine that allowed them to propel years ago. Its head was encased in This area of the body themselves. Later, in the Silurian Period, fish appeared that had a an impressive set of plates 1.2 inches had neither armor (3 cm) thick, with razor-sharp bony nor scales. jawbone. Known as the gnathostomata, they were large predators. plates that served as teeth. FIERCE JAW It had a lobed tail, similar Dunkleosteus was a to a shark's tail, which fierce predator that indicates that it was a CONICAL NOSE EYES devoured any type of powerful swimmer. Pteraspis Its streamlined shape Very small, prey, including sharks. helped the fish move. located on both DORSAL SPIKE The fish without a jawbone, sides of the head. Located on the fish's Pteraspis, was about 6.5 back, it worked like a inches (16 cm) long and lived in dorsal fin. It also had strong the seas of Europe, Asia, and North jaws with bony teeth. America. These fish were most abundant during the Devonian Period. They had bodies with armor that DORSAL SPINES covered their heads, and they had a These helped the fish streamlined shape. The shell had a co- to stay balanced while nical nose that helped the fish to move. swimming. 16 feet (5 m) 6.5 inches (16 cm) WING SHIELD LENGTH OF THE FISH Scientific Pteraspis name MOUTH TAIL Diet Small organisms Having no jawbone, The shape of the tail they fed on small Habitat Sea, then rivers and lakes helped balance the organisms. Range Europe, Asia, North America weight of the armor. Period Early Devonian cranium EVOLUTION OF THE JAWBONE The development of the jawbone was a The evolution of the jawbone LATERAL LINE long evolutionary process that involved modified the configuration Sensory organs are changes in the diet of fish to include not of the skull. present on both sides only small organisms but also other fish. of the body and on top of the armor. PRIMITIVE 1 VERTEBRATE The first fish Marine had no jawbone. lamprey Fossil Chimaeriformes Cheirolepis Pycnodus Sole Fish with lungs appeared in the Mesozoic Era Evolution Holocephali Cheirolepididae Pycnodontiformes Holostei Teleostei 2 ELASMOBRANCHIMORPH (200 million years ago). Wing shield The formation of the Similar to amphibians, these In the Devonian Period (Pteraspis) Dunkleosteus Sharks and rays Eusthenopteron Chondrostei NEOPTERYGII jawbone permitted new Placoderms species breathe with lungs ocean fish began to feeding habits, and the and are now considered diversify. Coelacanths appeared, Placoderms Elasmobranchii Sarcopterygii fish evolved from living fossils. The line as well as the earliest bony fish Lamprey herbivore to carnivore. through the center of the and the first cartilaginous fish, ACTINOPTERYGII Acanthodii pfihsho'tso laotf etrhael lfionses.il is the itnhcel utdhirnege smhaairnk sg.r Ionu pths iso fperiod Jawless CARTILAGINOUS FISH BONY FISH Devonian fish BONY FISH gnathostomad fish also 3 They already had a FOSSILIZED appeared: the placoderms, GNATHOSTOMATA specialized jawbone Modern fish LUNGFISH SCALES chondrichthyes, and THIS PERIOD SAW AN EXPLOSION IN like fish of today. Dipterus valenciennesi osteichthyes. VERTEBRATA THE DIVERSITY OF FISH SPECIES. 10 GENERAL CHARACTERISTICS FISH AND AMPHIBIANS 11 Distinguishing Features Near- Jawless Fish S fossils Of the ancient agnathans, considered imilar characteristics define nearly all fish, with a few rare exceptions. These aquatic the first living vertebrates, only Choanichthyes lampreys and hagfish are left. animals are designed to live underwater, and they have a jawbone and lidless eyes and are (Sarcopterygii) are archaic bony fish with fleshy fins. SEA LAMPREY cold-blooded. They breathe through gills and are vertebrates—that is, they have a spinal Some of them were the first Lampetra sp. animals with lungs. Only a column. They live in the oceans, from the poles to the equator, as well as in bodies of few species survive. Its round, toothed mouth fresh water and in streams. Some fish migrate, but very few can pass from salt allows it to suck the blood of fish of various species. There water to fresh water or vice versa. Their fins enable them to swim and move COELACANTH are also freshwater lampreys. Latimeria chalumnae in different directions. Animals such as dolphins, seals, and whales are This species was thought at times mistaken for fish, but they are actually mammals. to have gone extinct millions of years ago, until one was discovered Just Cartilage ANTERIOR alive off the coast of South DORSAL FIN Africa in 1938; more of This fin has stiff these fish were found later. Cartilaginous fish, such as rays and HEAD PECTORAL FIN rays and has a sharks, have extremely flexible One of the three Symmetrical, relatively small, stabilizing skeletons with little or no bone. EYES main divisions of and with a radial structure function. SCALES On the side of the its body The scales are POSTERIOR NASAL PITS head, protected by imbricateΩthat DORSAL FIN Also called fatty membranes is, they overlap This soft-structured RAY nares; lie on one another. fin is located Raja miraletus ethiteh ehre asdide of bfient wanede nth teh eta dilo.rsal Its large fins send currents of water carrying plankton and small fish to its mouth. The ray is very fast. LATERAL LINE Fish have sensory organs all along this line. With Spines MOUTH The angle of the mouth Osteichthyes is the most numerous affects what the fish class of fish. The skeleton has some can eat. level of calcification. OPERCULUM A bony flap that covers GILLS ATLANTIC MACKEREL the gills and helps The fish's Scomber scombrus regulate water flow breathing organs PELVIC FINS These permit the fish This fish has no teeth. It lives in to swim upward and temperate waters, and its meat is downward. considered delicious. It can live ANAL FIN Soft, with a row for more than 10 years. of finlets TAIL MUSCLE This is the Gill Breathing strongest muscle in the fish. CAUDAL FIN Gills are the organs that fish It moves from side use to breathe. They are made Filaments Water flow to side, propelling Gill raker Oxygenated the fish forward. of filaments linked by the gill arches. blood The fish uses its gills to take in oxygen dissolved in the water. In Action Water Open Water Closed Through a process known as diffusion, mouth mouth oxygen is transferred to the blood, Capillary Water enters the mouth and which has a lower concentration of Oedpgeen ionfg t ahte tubes felxotwrasc ot voexry tgheen ,g tilhlse. wAfatteerr tihse gills Pharynx 25,000 oxygen than the water. In this way operculum Blood expelled through the gill slits. the fish oxygenates its blood, flow which then circulates to the rest of Gills its body. In most bony fish Operculum us Is the number of known fish (taohnsedt emeixcoihuttsth hty,h esrspo)lu iwtgsha i tntehtroe f tlgowiwllo ss s liitntrs et.ahmrosu,gh Gill arch Gill filament Dbleoooxdygenated Filaments Ooppeennisn gasn dw chleorsee sw tahteer exits Esophag Coploesrecdulum Ooppeernculum shpaelfc ioefs a, lml cahkoinrgd autpe nsepaercliye so.ne