Biology

Chapter 25 Fish I. Vertebrates – animal with a backbone A. Characteristics 1. Show the 4 characteristics of all chordates at some point in their life. a. a notochord b. dorsal hollow nerve cord, c. pharyngeal slits d. post-anal tail. 2. Have an endoskeleton – an internal skeleton that grows with the animal. 3. Vertebrae – series of bones that surround the spinal chord. 4. Distinct Skull – contains a well developed brain and sensory organs. (cephalization) 5. A closed circulatory system with a multi-chambered heart.

B. Diversity 1. Ectotherms – body temperature is regulated mainly by the external environment a. Fish, amphibians, reptiles 2. Endotherms – capable of maintaining a constant body temperature. a. Convert food energy into heat & control heat loss II. Fish A. Adaptations to Water 1. Swim bladder – thin walled sac that can inflate or deflate. a. Allows the fish to move up or down or remain at a given depth. b. Sharks lack a swim bladder, so many must remain moving.

2. Well developed sense organs a. Sense of smell (olfactory organs) is advanced in some fish. 1) Sharks are capable of sensing smells from distances close to a mile b. Lateral line system – detects vibrations and changes in water pressure. B. Respiration & Circulatory System 1. Gills – collect oxgyen as water passes through them a. Process is helped by the opening and closing of the operculum, a movable flap of tissue that covers the gills. 1) Forces water to pass over the gills when mouth is opened and closed b. Blood vessels in the gills pick up the oxygen and carry it to a two-chambered heart. 1) Decreased efficiency as oxygen rich blood mixes with oxygen poor blood

C. Energy & Wastes 1. Most fish are carnivores a. Have movable jaws and teeth but do not chew their food. b. Food passes to the stomach whole and later is digested in the intestines. 2. Kidneys – eliminate wastes from the blood in the form of urine. a. Are also used to maintain a water balance. D. Reproduction 1. Fertilization can be internal or external. 2. External fertilization involves the female laying millions of eggs. a. Most eggs will never hatch. 1) Many are not fertilized, are eaten, or die before hatching.

III. Classes of Fish A. Agnatha – jawless fish 1. Are the only vertebrates that retain a notochord 2. Have long snake like bodies 3. Breathe through gill slits 4. Skeleton is made out of cartilage 5. Hagfish a. Feed on dead or dying fish 1) Drill a hole in the organism and suck out the blood and insides 2) Some will crawl inside the fish 6. Lampreys a. Have a round mouth with rows of sharp teeth. b. Attach to the host with teeth and feed off blood and body fluids.

B. Chondrichthyes – “cartilaginous fish” --- sharks, rays, skates 1. Have skeletons made almost entirely of cartilage 2. Range in size from less than a meter(skates) to 15 m in length (whale sharks) to 6 m across (manta ray) 3. Most are predators and built for hunting. C. Osteichthyes – “bony fish” 1. Majority of fish belong to this class 2. Are the most diverse group. 3. Lobe-finned fish – coelocanth a. Fins are similar to legs of early land vertebrates

4. Lung fish – has lungs as well as gills a. Live in shallow tropical waters. b. Some use lungs to supplement gills in murky water. c. Some use lungs when the pond or stream dries up. 5. Ray-finned – have fanlike fins. a. Walleye, northern, trout, salmon, tank fish, etc. III. Fish in the Biosphere A. Ecological Roles 1. Important role in the food chain a. Most help keep organism populations in check B. Human Uses 1. Food a. Good source of protein with limited cholesterol b. Helps in the reduction of heart disease