Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall
30-2 Fishes Photo Credit: © Art Wolfe/Stone Copyright Pearson Prentice Hall

What Is a Fish? What Is a Fish? Fishes are aquatic vertebrates. Most fishes have paired fins, scales, and gills. Fishes are so varied that for almost every general statement there are exceptions (ie: catfish don’t have scales) Fishes come in many shapes and sizes. Like most fishes, this African cichlid has paired fins, scales, and gills. Photo Credit: ©Labat-Lanceau/AUSCAPE International Copyright Pearson Prentice Hall

Evolution of Fishes Evolution of Fishes Fishes and nonvertebrate chordates probably evolved from common invertebrate ancestors. The evolution of jaws and the evolution of paired fins were important developments during the rise of fishes. The First Fishes The earliest fishes to appear in the fossil record lived about 510 million years ago. These fishes were jawless and had bodies covered with bony plates. Copyright Pearson Prentice Hall

Evolution of Fishes The Age of Fishes During the Ordovician and Silurian Periods, million years ago, fishes underwent a major adaptive radiation. These species then ruled the seas during the Devonian Period, often called the “Age of Fishes”. Some fishes were jawless species that had very little armor. These are the ancestors of modern hagfishes and lampreys. Armored fishes became extinct at the end of the Devonian Period. Copyright Pearson Prentice Hall

The Arrival of Jaws and Paired Fins
Evolution of Fishes The Arrival of Jaws and Paired Fins The evolution of jaws in fish was extremely useful. Jaws with muscles and teeth made it possible for fish to eat a wider variety of foods. Animals with jaws can also defend themselves by biting. Fishes evolved paired pectoral (anterior) and pelvic (posterior) fins. Copyright Pearson Prentice Hall

Evolution of Fishes These fins were attached to girdles—structures of cartilage or bone that support the fins. Cartilage is a strong tissue that supports the body and is softer and more flexible than bone. Paired fins gave fishes more control of body movement. Tail fins and powerful muscles gave fishes greater thrust when swimming. Copyright Pearson Prentice Hall

The Rise of Modern Fishes
Evolution of Fishes The Rise of Modern Fishes Early jawed fishes soon disappeared, but left behind two major groups that continued to evolve and still survive today. One group—the ancestors of modern sharks and rays—evolved a skeleton made of strong, resilient cartilage. The other group evolved skeletons made of true bone. A subgroup of bony fishes, called lobe-finned fishes, had fleshy fins from which the limbs of chordates would later evolve. Copyright Pearson Prentice Hall

Form and Function in Fishes
Adaptations to aquatic life include various modes of feeding, specialized structures for gas exchange, and paired fins for locomotion. Copyright Pearson Prentice Hall

Feeding Every mode of feeding is seen in fishes. A single fish may exhibit several modes of feeding, depending on the type of food available, or be extremely specialized in their food preference. Copyright Pearson Prentice Hall

Food passes through the mouth and esophagus, into the stomach. In the stomach, the food is partially broken down. Esophagus Stomach The internal organs of a typical bony fish are shown here. Mouth Copyright Pearson Prentice Hall

In many fishes, the food is further processed in fingerlike pouches called pyloric caeca. The pyloric caeca secretes digestive enzymes and absorbs nutrients from the digested food. Pyloric cecum The internal organs of a typical bony fish are shown here. Copyright Pearson Prentice Hall

The liver and pancreas add enzymes and other digestive chemicals to the food as it moves through the digestive tract. Liver Pancreas Copyright Pearson Prentice Hall

The intestine completes the process of digestion and nutrient absorption. Intestine Only show “Intestine” label on this slide. Copyright Pearson Prentice Hall

Undigested material is eliminated through the anus. Anus Copyright Pearson Prentice Hall

Respiration Most fishes exchange gases using gills located on either side of the pharynx. The gills are made up of feathery, threadlike structures called filaments. Each filament contains a network of fine capillaries that provide a large surface area for exchange of gases. Gills Copyright Pearson Prentice Hall

Fishes use their gills to exchange gases by pulling oxygen-rich water in through their mouths, pumping it over their gill filaments, and pushing oxygen-poor water out through openings in the sides of the pharynx. Gills Copyright Pearson Prentice Hall

Some fishes, such as lampreys and sharks, have several gill openings. Most fishes have a single gill opening on each side of the body through which water is pumped out. This opening is hidden beneath a protective bony cover called the operculum. Some fish have specialized organs that serve as lungs to adapt to oxygen-poor water. A tube brings oxygenated-air to the organ through the fish’s mouth. Copyright Pearson Prentice Hall

Circulation Fishes have closed circulatory systems with a heart that pumps blood around the body in a single loop from the heart to the gills, from the gills to the rest of the body, and then back to the heart. In most fishes, the heart has four parts: sinus venosus atrium ventricle bulbus arteriosus Copyright Pearson Prentice Hall

Sinus Venosus Oxygen-poor blood from the veins collects in the thin walled sinus venosus before it flows to the atrium. Copyright Pearson Prentice Hall

The atrium is a large muscular chamber that serves as a one-way compartment for blood that is about to enter the ventricle. Blood enters the atrium and flows to the ventricle. Atrium Copyright Pearson Prentice Hall

The ventricle is a thick-walled, muscular chamber that is the actual pumping portion of the heart. The ventricle pumps blood into the bulbus arteriosus. Ventricle Copyright Pearson Prentice Hall

The bulbus arteriosus is a large muscular tube that moves blood into the ventral aorta and toward the gills. It connects at its front end to a large blood vessel called the aorta, through which blood moves to the fish’s gills. Bulbus arteriosus Copyright Pearson Prentice Hall

Circulation in a Fish Gills Brain and head circulation Body muscle circulation Blood circulates through a fish’s body in a single loop—from the heart to the gills to the rest of the body, and then back to the heart again. Digestive system circulation Heart Copyright Pearson Prentice Hall

Excretion Fishes eliminate nitrogenous wastes as ammonia. Some wastes diffuse through the gills into the surrounding water. Others wastes are removed by kidneys, which are excretory organs that filter wastes from the blood. Kidneys help fishes control the amount of water in their bodies. Some fishes can move from fresh to salt water by adjusting their kidney function. Copyright Pearson Prentice Hall

Salt water fishes tend to lose water by osmosis. The kidneys of marine fishes concentrate wastes and return water to the body. Kidney The internal organs of a typical bony fish are shown here. Copyright Pearson Prentice Hall

Freshwater fishes tend to have a great deal of water entering their bodies by osmosis. The kidneys of freshwater fishes pump out dilute urine. Kidney Copyright Pearson Prentice Hall

Response Fishes have well-developed nervous systems organized around a brain, which has several parts. Brain The brain of a fish, like all vertebrate brains, is situated at the anterior end of the spinal cord and has several different parts. Copyright Pearson Prentice Hall

The most anterior parts of the brain are olfactory bulbs. They are involved with the sense of smell, or olfaction. Olfactory bulbs are connected to the lobes of the cerebrum. Olfactory bulb Copyright Pearson Prentice Hall

In most vertebrates, the cerebrum is responsible for all the voluntary activities of the body. In fishes, however, the cerebrum primarily processes the sense of smell. Cerebrum Copyright Pearson Prentice Hall

The optic lobes process information from the eyes. The cerebellum coordinates body movements. The medulla oblongata controls the functioning of many internal organs. Optic lobe Cerebellum Medulla oblongata Copyright Pearson Prentice Hall

Almost all fishes that are active in daylight have well-developed eyes and color vision that is at least as good as humans’. Many fishes have extraordinary senses of taste and smell due to specialized cells called chemoreceptors. Most fishes have ears but may not hear sounds well. Copyright Pearson Prentice Hall

Fishes use the lateral line system to sense the motion of other fishes or prey swimming nearby by detecting gentle currents and vibrations in the water. Some fishes can detect low levels of electric current, like catfish and sharks. Some fish can even generate their own electricity, like the electric eel. Copyright Pearson Prentice Hall

Movement Most fishes move by contracting paired sets of muscles on either side of the backbone. Series of S-shaped curves move down the fish’s body. Force and action of the fins propels the fish forward. The fins of fishes are used to keep on course and adjust direction. Fins also increase the surface area of the tail, providing an extra boost of speed. Fishes’ streamlined body shapes reduce the amount of drag (friction) as they move through water. Copyright Pearson Prentice Hall

Fishes’ body tissues are more dense than the water they swim in, so sinking is an issue. Many bony fishes have an internal, gas-filled organ called a swim bladder that adjusts their buoyancy. The internal organs of a typical bony fish are shown here. Copyright Pearson Prentice Hall

Reproduction The eggs of fishes are fertilized either externally or internally, depending on the species. Fishes whose embryos in the eggs develop and hatch outside the mother's body are oviparous, like salmon. The embryos of oviparous fishes obtain food from the yolk in the egg. In ovoviviparous species, such as guppies, the eggs stay in the mother's body after internal fertilization. Each embryo develops inside its egg, using the yolk for nourishment. The young are “born alive” like most mammals. Copyright Pearson Prentice Hall

In viviparous animals, like several shark species, the embryos stay in the mother's body after internal fertilization. These embryos obtain the substances they need from the mother's body (not from material in an egg). The young of viviparous species are “born alive.” Copyright Pearson Prentice Hall

Groups of Fishes Groups of Fishes Over 24,000 living species Grouped according to body structures All living fishes can be classified into three groups: jawless fishes, cartilaginous fishes, and bony fishes. Copyright Pearson Prentice Hall

Groups of Fishes Jawless Fishes Superclass Agnatha Jawless fishes have no true teeth or jaws. Their skeletons are made of fibers and cartilage. They lack vertebrae, and keep their notochords as adults. Copyright Pearson Prentice Hall

Groups of Fishes Modern jawless fishes are divided into two classes: lampreys and hagfishes. Photo Credit: Animals Animals/©Zig Leszczynski Lamprey Copyright Pearson Prentice Hall

Class Cephalaspidomorphi
Groups of Fishes Class Cephalaspidomorphi Lampreys are typically filter feeders as larvae and parasites as adults. Adult lampreys attach themselves to fishes, whales, and dolphins. They scrape away at the skin with small tooth-like structures that surround the mouth and with a strong, rasping tongue. The lamprey sucks up the tissues and body fluids of its host. Copyright Pearson Prentice Hall

Groups of Fishes Class Myxini Hagfishes have pinkish gray, wormlike bodies and four or six short tentacles around their mouths. They lack eyes, but have light-detecting sensors scattered around their bodies. They feed on dead and dying fish by using a toothed tongue to scrape a hole into the fish’s side. They secrete incredible amount of slime, have six hearts, an open circulatory system, and regularly tie themselves into knots. Copyright Pearson Prentice Hall

Sharks and Their Relatives
Groups of Fishes Sharks and Their Relatives The class Chondrichthyes contains sharks, rays, skates, sawfishes, and chimaeras. The skeletons of these fishes are built entirely of cartilage. Most cartilaginous fishes have tooth-like scales covering their skin, making I as rough as sandpaper. Many sharks have large curved tails, torpedo-shaped bodies, pointed snouts with the mouth underneath, and thousands of teeth arranged in several rows. Most species of sharks do not attack people. Copyright Pearson Prentice Hall

Groups of Fishes Some skates and rays feed on bottom-dwelling invertebrates using their mouths as powerful vacuums. The largest rays eat floating plankton. Skates and rays glide through the sea with flapping motions of their large, wing-like pectoral fins. Many skates and rays cover themselves with sand and rest on the ocean floor. Copyright Pearson Prentice Hall

Groups of Fishes Bony Fishes Class Osteichthyes Their skeletons are made of hard, calcified bone. Almost all living bony fishes are ray-finned fishes. “Ray-finned” refers to the slender bony spines, or rays, that are connected by a thin layer of skin to form the fins. Copyright Pearson Prentice Hall

Groups of Fishes Only seven living species of bony fishes are not classified as ray-finned fishes. These are the lobe-finned fishes, a subclass that includes lungfishes (freshwater) and the coelacanth (saltwater). The fleshy fins of lobe-finned fishes have support bones. Some of these bones are jointed, like the arms and legs of terrestrial vertebrates. Copyright Pearson Prentice Hall

Ecology of Fishes Some fishes spend most of their lives in the ocean but migrate to fresh water to breed. These fish are called anadromous. Salmon, lampreys, and sturgeons are anadromous. Some fishes spend most of their lives in the freshwater but migrate to saltwater to breed. These fish are called catadromous. European eels are catadromous. Photo credit: ©Ralph A. Clevenger/CORBIS Copyright Pearson Prentice Hall

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