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Section 2: Fish
Vocabulary:
 Fin: Fanlike structures attached to the endoskeleton; used for steering, balancing, and moving
 Scale: Hard, thin plats that cover the skin and protect the body
Concepts
Fish Characteristics:
 More species of fish that any other group of vertebrates
 Ectotherms
 Nearly adapted to live in any aquatic environment
 Found in varying depths of water
 Streamline shape, a muscular tail, and fins used for movement
o Fins on side used for directional movement
o Fins top and bottom used for stability
o Most secrete a mucus that also helps to move through water
 Most scales are made of bone
o Can be toothed shaped, diamond shaped, cone shaped, or round
 Shape can be used to help classify fish
 The age of some species can be estimated by counting the annual growth rings of the
scales
 Body Systems: Highly developed sensory systems
o Lateral line system: enables a fish to sense its environment, and to detect movement
o Can have a strong sense of smell: Sharks sensing blood from several kilometers away
 Gas Exchange: Gills located on both sides of the head
o Used to take in water and exchange oxygen from the water with carbon dioxide from the
blood
 Feeding Adaptations: Diverse adaptations for obtaining food
o Some fish have strong teeth, but most do not chew their food but instead use the to capture
prey or to tear off chunks of food
 Reproduction: Reproduce sexually
o Production of sex hormones is dependent on certain environment factors such as temperature,
length of daylight, and availability of food
o Females release a large number of eggs into water; males swim over eggs and release sperm
 Development outside a body is known as external fertilization
o Certain species undergo internal fertilization
o Some species do not take care of their young
 Produce hundreds or millions of eggs in the hopes some will survive
Jawless Fish:
 Lampreys, hagfish, etc.
 Round, toothed mouths, and long, tubelike bodies covered with scaleless, slimy skin.
 Most lampreys are parasites
o Attach to other fish with suckerlike mouth
 Hagfish feed on dead or dying fish and other aquatic animals
 Flexible endoskeleton made of cartilage
Jawed Cartilaginous Fish:
 Sharks, skates, and rays
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Endoskeleton made of cartilage
Moveable jaw with well developed teeth
Body covered with tiny scales that make their skin feel like sand paper
Sharks are usually top predators in food chains
Shark populations are decreasing at a substantial rate due to over fishing
Bony Fish:
 95% of all fish species are bony fish. Three types of bony fish
o Lobe-finned, lungfish, ray-finned
 Skeletons made of bone
 Swim Bladder: air sac that allows the fish to adjust its density in response to the density of the
surrounding water
o Density: Greater (sink), lesser (float to top), or equal (neither float to top or sink to bottom)
o As the swim bladder fills with gas, fish float towards the surface
o As it deflates, fish sink towards the bottom
o Some bottom-dwelling fish and active fish do not have a swim bladder
 Lobe-Finned Fish: fins that are lobelike and fleshy
 Lungfish: has 1 lung, as well as gills
o Lung adaptation allows them to live in shallow waters that does not contain a lot of oxygen
o Drought conditions cause them to burrow into the mud and cover themselves with mucus
until water returns
 Ray-Finned Fish: fins made of long, thin bones covered with skin
o Predatory fish have long, flexible bodies, which enable them to pursue prey quickly
o Many bottom fish have flattened bodies and mouths adapted for eating off the bottom
Importance and Origins of Fish
 Provide food
 Important to many economies
 Recreational enjoyment (fishing)
 Keep insect population in check
 Keep plant growth from clogging waterways
 Originate in the fossil record ~450 mya