March 27, 2012 Chapter 39: Fishes Section 1 Introduction to Vertebrates Section 2 Jawless and Cartilaginous Fishes Section 3 Bony Fishes 39-1 Introduction to Vertebrates Objectives: Identify the distinguishing characteristics of vertebrates. List an example for each of the nine classes of vertebrates. Describe the characteristics of the early vertebrates. Explain the importance of jaws and paired fins for fishes. Characteristics Vertebrates are members of the subphylum Vertebrata, within the phylum Chordata. All Chordates share the following characteristics. · Notochord · Dorsal hollow nerve cord · Pharyngeal gill slits · Post-anal tail March 27, 2012 Characteristics of Vertebrates Vertebrates are distinguished from chordates by: Vertebrae - bones or cartilage that surround the dorsal nerve cord and form the spine. A cranium - a skull that protects the brain An endoskeleton - an internal skeleton made of bone or cartilage Types of Vertebrates Vertebrates are divided into nine classes: (know these! Common names are fine) (45,000 species total) Class-example · Myxini - hagfishes · Cephalaspidomorphi - lampreys · Chondrichthyes - sharks, rays, skates, and ratfishes · Actinopterygii - ray-finned fishes · Sarcopterygii - lobe-finned fishes (2 groups) · Amphibia - frogs, toads, salamanders, and caecilians (4880 sp) · Reptilia - lizards, snakes, and turtles (8000 species) · Aves - birds (10,000 species) · Mammalia - mammals (4400 species) Ichthyology? March 27, 2012 Vertebrate Evolution Most biologists think that vertebrates originated about 560 million years ago. The first fish were jawless. About 450 million years ago, the first fishes with jaws and paired fins appeared. Jaws are thought to have evolved from the first pair of gill arches, the skeletal elements that support the pharynx. The advantages to jaws and paired fins: · Paired fins increased fishes’ stability and maneuverability in water · Jaws allowed fishes to seize and manipulate prey Advantages of Paired Fins Origin of Jaws March 27, 2012 39-2 Objectives Identify three characteristics that make fishes well suited to aquatic life. Describe three sensory systems in fish. Evaluate the similarities between jawless fishes and early vertebrates. Identify two characteristics of cartilaginous fishes. Contrast reproduction in lampreys with reproduction in cartilaginous fishes. Fish Adaptations Fish have several adaptations that make them well suited to life in water: · Streamlined body plan - allows fish to move rapidly in water · Adaptations for buoyancy - stored gases or lipids help maintain vertical position in water · Efficient respiration - internal gills exchange gases efficiently Fish Characteristics Fish Adaptations, continued Adaptations for salt and water homeostasis - · The concentration of solutes in a fish’s body usually differs from the concentration of solutes in the water. · Fish have adaptations to maintain ion and water homeostasis. March 27, 2012 Fish Adaptations, Continued Sensory adaptations - Fish have a variety of organs that allow them to sense their environment. Sight: fish eyes are similar to eyes of land vertebrates Sound: fish have internal ears sensitive to sound Chemoreception: the ability to detect chemicals in the environment includes the senses of smell and taste. Fish have nostrils and tastebuds. Tastebuds may be located in their mouths, on their lips, fins, and skin, and on whisker-like organs called barbels. Fish Adaptations, Continued Unique senses: Lateral line: the lateral line is a system of canals in the skin that allow fish to sense vibration in the water Ampulae of Lorenzini: cartilaginous fishes have sense organs called ampulae of Lorenzini that can detect weak electrical fields Electroreception and Magnetoreception: some fish have the ability to detect electrical and magnetic fields Lateral Line System Lateral Line in Fishes March 27, 2012 Jawless Fishes Only two classes of jawless fishes are alive today: Hagfishes Lampreys Hagfishes (class Myxini) · Hagfishes are bottom-dwellers that feed on dead and dying fish. Hagfish Slime Lampreys (class Cephalaspidomorphi) · Lampreys can be free-living or parasitic. · Parasitic lampreys attach themselves to their host with disc- shaped mouths and feed on the blood and body fluids of other fishes. · All lampreys breed in fresh water. · Fertilization occurs outside the body - external fertilization. Lamprey PSA Cartilaginous Fishes All cartilaginous fishes: belong to the class Chondrichthyes. have skeletons made of cartilage - a flexible lightweight material made of cells surrounded by tough fibers of protein. have skin covered with placoid scales - small, toothlike spines that feel like sandpaper. Placoid scales probably reduce turbulence and increase swimming efficiency. page 784 March 27, 2012 Cartilaginous Fishes, Continued Sharks: Sharks have torpedo shaped bodies that reduce turbulence when swimming, called a fusiform body shape. Some sharks are filter feeders, and have slender projections on the inner surface of their gills, called gill rakers, that filter the water. The mouth of a typical shark has 6 to 20 rows of teeth. When a tooth breaks or wears down, a replacement moves forward. One shark may use more than 20,000 teeth over its lifetime. Shark Senses Cartilaginous Fishes, Continued Rays and Skates: Rays and skates have flattened bodies with paired wing-like pectoral fins and, in some species, whip-like tails. Rays have diamond- or disk-shaped bodies. Most skates have triangular bodies. Rays and skates are primarily bottom dwellers, and most feed on mollusks and crustaceans. Cartilaginous Fishes, Continued Ratfishes: Ratfishes are a small group of strange looking fish that have a flap of skin covering their gill slits. Ratfishes have long, rat-like tails and feed on crustaceans and mollusks. March 27, 2012 Cartilaginous Fishes, Continued Adaptations in Cartilaginous Fishes: Some sharks push water through their mouth and over their gills by swimming. Most cartilaginous fish pump water over their gills by expanding and contracting their mouth cavity and pharynx. When lying on the bottom, rays and skates draw water in to their gills through spiracles, two large openings on the top of the head, behind the eyes. Cartilaginous Fishes, Continued Adaptations in Cartilaginous Fishes: Sharks convert ammonia to urea in their bodies. Sharks retain large amounts of urea in their bodies to raise the concentration of solutes in their bodies to the same level as that found in sea water. Sharks still tend to take up sodium and chloride ions. The rectal gland removes excess sodium and chloride ions from the body. Anatomy of a Shark Cartilaginous Fishes, Continued Adaptations in Cartilaginous Fishes: Cartilaginous fishes maintain their position in the water in two ways: · The caudal and pectoral fins generate lift, or upward force, as the fish swims. · Many cartilaginous fish store large amounts of lipids, usually in the liver. Lipids are less dense than water. March 27, 2012 Cartilaginous Fishes, Continued Reproduction in Cartilaginous Fishes: Fertilization occurs inside the body of the female, called internal fertilization. Some cartilaginous fish lay eggs. The eggs of many species develop within the female’s body. In some species, the mother nourishes the developing young while they are in her body. 39-3 Bony Fishes Objectives: List three characteristics of bony fishes. Distinguish between lobe- finned fishes and ray-finned fishes. Describe three key features of bony fishes’ external anatomy. Summarize the major body systems in bony fishes. Describe the function of the swim bladder. Discuss reproduction in bony fishes. Characteristics of Bony Fishes Bony fishes have three key features: Bone - the skeletons of most bony fishes contain bone. Lungs or swim bladder - early bony fishes had lungs, organs which exchange gas between the air and blood. Most bony fishes today have a swim bladder, a gas- filed sac that is used to control buoyancy. Scales - scales protect the body of a bony fish and reduce friction when swimming. March 27, 2012 Swimbladder in Bony Fishes Primitive Bony Fishes Swim Bladder is connected directly to the Pharynx. Swim bladders in more recently evolved fishes is controlled by diffusion of gasses through a capillary bed. Advantage: Control of bouyancy without having to surface. Allows exploitation of deeper niches. Compare Pectoral Fin Locations Characteristics of Bony Fishes, continued There are two main groups of bony fishes: · Lobe-finned fishes - have fleshy fins supported by a series of bone. · Ray-finned fishes - have fins that are supported by long, segmented, flexible bony elements called rays. March 27, 2012 External Anatomy Operculum Most bony fish have an operculum, a hard plate that opens at the rear and covers and protects the gills. Fins The fins of most fish are supported by rays or spines. · Rays are flexible, spines are rigid. Skin The skin of most bony fish are covered with scales. · Scales are thin, round disks of a bonelike material that grow from pockets in the skin and overlap like shingles. urogenital Internal Anatomy Digestive system Food passes from the mouth into the pharynx, through the esophagus, to the stomach. From the stomach food passes into the intestine, where nutrients are absorbed. Undigested material is eliminated through the anus. March 27, 2012 Yellow Perch Internal Anatomy Internal Anatomy, Continued Circulatory system The circulatory system of a fish delivers oxygen and nutrients to the cells of the body. The circulatory system consists