Fish

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Kingdom – Animalia
Phylum – Chordata
Subphylum – Vertebrata
Vertebrates:
| Include fish, amphibians, reptiles, birds, & mammals |
| Have a notochord (slim, flexible rod) present in early stages that may be replaced by backbone in adults |
| Contain a dorsal, hollow bundle of nerves called the nerve or spinal cord |
| Respire through pharyngeal or gill pouches during early development |
| Have post-anal tail in early stages |
| Endoskeleton made of bone &/or cartilage |
| Anterior head with well developed brain & sensory organs (Cephalization) |
| Closed circulatory system |
Taxonomy of Vertebrates:
| Agnatha include hagfish & lamprey with long, eel-like bodies without jaws or paired fins & cartilage skeletons |

| Chondrichthyes include sharks, rays, & skates with cartilage skeletons, paired fins, & jaws |

| Osteichthyes are bony fish with jaws, paired fins, & bone and cartilage in their skeletons |
| Amphibia include frogs, toads, & salamanders that go through an aquatic larval or tadpole stage |
| Reptilia include snakes, turtles, lizards, & alligators that live on land, are covered with scales, & lay a tough, protective amniote egg |
| Aves are birds covered with feathers, adapted for flying, & with hollow bones |
| Mammalia have hair or fur & females have mammary or milk-producing glands |
Evolution:
| Fossil record shows jawless fish without paired fins appeared first about 550 million years ago |
| Ostracoderm was a jawless, bottom-feeding ancestor to the agnathans (modern jawless fish) |

| Development of jaws & paired fins allowed better movement & increased ability to capture prey |
| Extinct acanthodians or spiny fish were first jawed fish with paired fins |

| Jaws probably developed from gill arches (bone that supports the pharynx) |
Characteristics of Fish:
| Streamlined body & muscular tail for swimming |
| Most with paired fins for maneuvering |
| Body covered with protective scales & mucus layer to reduce friction when swimming |
| Have less dense body tissues & store less dense lipids to help them float |
| Respire through gills |
| Most have a lateral line system or a row of sensory structures running down each side of the organism to detect changes in water temperature, pressure, current, etc. |

| Most with well-developed sense of sight & smell |
| Some can detect electrical currents |
| Ectotherms (adjust body temperature to environment) |
| Two chambered heart (upper atrium receives blood & lower ventricle pumps blood) |
Agnatha (Jawless Fish):
| Hagfish (live in oceans) & lampreys (found in marine & freshwater) |
| Circular mouths |
| Sharp teeth & strong rasp-like tongue to tear hole in prey & suck out blood & body fluids |

| Known as cyclostomes |
| Eel-shaped body |
| Mucus covers body |
| Skeleton made of cartilage |
| No paired fins |
| Gills without bony cover (called operculum) |
| Retain their notochord throughout their life |
| Hagfish are bottom dwellers in cold marine waters that burrow in mud, scavenge on dead & dying fish, & have tentacles around their mouth |
| Lampreys are usually parasites with a keen sense of smell to locate prey, lay their eggs in freshwater streams, & are covered with a poisonous slime |
Chondrichthyes
| Includes sharks, rays, & skates |
| Endoskeleton of cartilage |
| Hinged jaws & paired fins |
| Placoid scales & tooth-like dermal spines on scales |

| Marine |
| Carnivorous |
| Sharks are torpedo shaped |

| Rays & skates have broad, flat bodies with wing-like fins and a tail |

Shark Characteristics:
| Fast swimmers |
| Large, oily liver (20% of body weight) makes them buoyant |
| Tough, leathery skin |
| Fierce predators |
| Whale shark is largest & filter feeds on plankton |

| Ventral mouth with 6-20 rows of sharp, replaceable teeth |
| Short, straight intestine with spiral valve to slow food movement |
| 5-7 pairs of gills for gas exchange |
| Kidneys remove wastes & maintain water balance |
| Electroreceptors on head help find prey & navigate |
| Lateral line along side of body contains sensory cells to detect vibrations & pressure |
| Separate sexes with external fertilization |
Ray & Skate Characteristics:
| Usually harmless to humans |
| Broad, wing-like pectoral fins used to glide through water |
| Flattened bodies with ventral mouth |
| Both eyes on top of head |
| Have protective coloration (darker on top & lighter on bottom) |
| Feed on fish & invertebrates |
| Stingray with poison spine by tip of tail |

| Electric ray gives off strong, electric shock |
| Manta ray is largest |
Traits of Bony Fish (Osteichthyes)
| Skeleton made of bone |
| Hinged jaws |
| Paired fins |
| Gills for gas exchange |
| Lateral line |
| Body covered with scales & mucus coating |
| Includes lobe-finned, ray-finned, and lung fish |
Lobe-finned Fish:
| Muscular, paddle-like fins supported by bone |
| Gills |
| Known as coelacanths |

| Thought to be extinct until 1938 when species found in Africa |
| Live in deep oceans |
Lungfish:
| Use lungs & gills |
| Eel-shaped body |

| Live in shallow, tropical rivers of Africa, Australia, & South America |
| Come to surface & gulp air when oxygen level is low |
| Form mud cocoon & become dormant if stream dries up |
Ray-finned Fish: 
| Fan-like fins supported by rays |
| Includes salmon, perch, catfish, tuna, etc. |
| Body covered with round, overlapping cycloid or ctenoid scales & mucus |

| Four sets of gills covered by bony operculum |

| Have movable fins |
| Dorsal fin(s) located on top keep fish upright & used for defense |
| Caudal fin or tail moves side to side to help steer |
| Pectoral fins (paired) on each side behind the operculum |
| Pelvic fins (paired) on ventral surface near the head |
| Anal fin (single) behind anus |

| Swim bladder is thin-walled sac in abdomen that creates buoyancy from diffusion of dissolved gas from blood |

| Kidneys filter the blood & help maintain water balance |
| Ectothermic – body temperature regulated by the environment |
| Keen sense of smell (nostrils) & have chemical receptors over the body |
| Can detect the earth’s magnetic field as a guide to navigate oceans |
| Have separate sexes with external fertilization |
| Eggs hatch into fry |

Salmon Life Cycle:
| Migrate up to 3200 kilometers following magnetic cues in the ocean |
| Follow mucus trails when navigating rivers |
| Return to birthplace to spawn |
| Males change color & jaw lengthens & develops a hook |

| Female uses her tail to build gravel nest & lays up to 10,000 eggs |
| Male deposits sperm over eggs |
| Adults usually die after spawning |
| Pacific salmon return to sea when 15 cm long; while Atlantic salmon may stay in river up to 7 years |
| Secrete mucus coating in river as return to sea |
| May stay in ocean 6 months to 5 years |