Marine Fishes- Basics of
Ichthyology
Chapter 8

How are Humans and Sea Squirts related?
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Subphylum urochordata- sea squirts.
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Phylum Chordata
• Not all Chordates are vertebrates!
• Characteristics of Chordates:
• 1.) Dorsal nerve cord
• 2.) Notochord
• 3.) Gill slits
• 4.) Post-anal Tail
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Basic Chordate plan
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Lancelets- Simple Chordates
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Subphylum vertebrata
• Have the 4 major characteristics of chordates.
• Also have vertebrae that protect the dorsal nerve cord (spinal cord).
• Bilateral symmetry
• Fish-oldest vertebrates found in the fossil record.
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Figure 8.01
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Class Agnatha- jawless fish
• Have no jaws- feed by suction of round mouth.
• Long, slender body (like an eel)
• Lack paired fins and scales.
• Hagfishes- feed on dead or dying fish.
Sometimes bore into their prey and eat from the inside out.
• Lampreys- mostly freshwater- parasitic feeders.
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Pacific hagfish
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Pacific hagfish
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Lampreys
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Class Chondrichthyes- cartilaginous fish
• Sharks, rays, skates and ratfishes.
• Cartilage skeletons- lighter and more flexible than bone.
• Placoid scales- have a pointed, sometimes sharp tip.
• Caudal fin (tail fin)- top lobe is larger than the bottom lobe. This is called a heterocercal fin.
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Class Chondrichthyes- (cont’d)
• Most cartilaginous fish have two dorsal fins.
• Large, pointed, fleshy pectoral fins.
• Five to seven gill slits on each side.
• Many rows of triangular teeth.
• As teeth are lost, a tooth from the row behind it moves forward.
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External anatomy of a shark
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Figure 8.04
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Galapagos Hammerhead
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Great White Shark
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Great White Sharks
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Bull Shark
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Bull Shark
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White tip reef shark
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Skates and rays
• 450-550 Species
• Mostly demersallive on the bottom.
• Rays have their gill slits on their ventral side.
• Pectoral fins are very large and flat, like bat wings.
• Spiracles aid in gill irrigation.
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Rays- (cont’d)
• Stingrays- Whip-like tail with stinging spines for defense.
• Poison gland produces the venom.
• Bury themselves in the sand and feed upon molluscs and crustaceans.
• Have specialized teeth for grinding shells of prey.
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Manta Ray and Diver
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Spotted Eagle Ray
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Blue Spotted Stingray
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Southern Stingray
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Class Osteichthyes- bony fish
• The majority of fishes- 96%. Almost half of all vertebrates are bony fishes.
• Have cycloid, or ctenoid scales- thin, flexible and overlapping. They are smooth to the touch.
• Operculum- a flap of bony plates and tissue that cover the gills.
• Fins- thin membranes instead supported by bony spines, or fin rays.
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Class Osteichthyes- cont’d
• Mouth is usually terminal (at the end of its head)
• Caudal fin is usually homocercal- both lobes the same size.
• Swim bladder- gas filled sac above the stomach. Helps with buoyancy.
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External anatomy of a bony fish
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Body shape of fishes
• Related to its lifestyle
• Streamlined for constant swimming- ex tuna and mackerel.
• Laterally compressed- maneuverabilityaround reefs ex- damselfish, (our fish)
• Flattened- good for demersal fish and rays.
• Eel-shaped – good for living around rocks and for quick propulsion.
• Irregular shapes aid in camouflage
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Streamlined shape
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Yellowfin tuna
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Flattened shape
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Japanese Flounder
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Leafy Sea Dragon
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Damselfish and Tangs- Laterally compresed
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Eel shaped
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European eel
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Coloration
• Chromatophores- special cells in the skin that contain pigments.
Irregular in shape with branches
Some fish can contract and expand the pigment to rapidly change color
• Iridiophores- special chromatophores that contain reflective crystals.
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Winter Flounder on a checkerboard background
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Coloration (cont’d)
• Warning coloration- indicates toxins or danger.
• Cryptic coloration- blending in with the environment to avoid predation
• Disruptive coloration- colored bars, stripes or spots that break up the outline of a fish. Intended to confuse predators.
• Countershading- found in open water fishdark on dorsal side, silvery on ventral side.
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Warning coloration
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Cryptic coloration- flounder
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Disruptive Coloration- Four-Eye
Butterfly fish and Ornate Cowfish
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Locomotion
• Swim with a side to side S-shaped motion using muscles called myomeres.
• Pectoral fins- provide lift in sharks, not in bony fish (why?)
• Dorsal and anal fins- used as rudders
• Pelvic fins- help turn, balance, and “brake”
• Flexibility of fins allow some bony fish to use other methods of swimming.
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Undulating “S-shaped” swimming- gives the ability to maneuver rocky habitats
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Tuna swim fast by flexing their caudal fins.
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Many reef fish use movement of fins to move precisely in feeding habitats
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This trunkfish can only swim slowly by moving only the end of the caudal fin.
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Locomotion in cartilaginous fish
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Locomotion in bony fish
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Feeding- mouth adaptations
• Sharks- mostly carnivores- often feed on prey larger than themselves.
• Some are filter feeders- whale shark, megamouth shark, manta rays.
• Carnivorous fish-well-developed teeth for catching and holding prey.
• Grazer- feed primarily on seaweeds
• Plankton feeders- filter plankton over structures called gill-rakers.
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Mouth adapted for taking bites out of large prey
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Butterfly fish eat very small prey
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Parrotfish have a beak-like mouth for scraping algae and corals
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Herring have large mouth for filtering plankton
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Circulation
• All fishes have a two-chambered heart, located below the gills.
• The first chamber collects deoxygenated blood from the body.
• The second chamber pumps this blood to the gills for gas exchange.
• Fish have a closed circulatory system of arteries, veins and capillaries.
• Sharks- have low blood pressure and use muscle contraction to aid in circulation.
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Figure 8.15
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Respiration- irrigation of the gills
• Sharks- most take in water through the mouth AND the Spiracles.
• Skates and rays-spiracles on the dorsal side take in water when on the bottom.
• Bony fish- draw water in by opening and closing the operculum and by the expansion and contraction of the pharynx.
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Figure 8.16b
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Countercurrent system
• Oxygen enters blood by diffusion.
• There must be a lower concentration of oxygen in the blood in order for diffusion to occur.
• The blood in the gills flows opposite to the direction of the water.
• This makes respiration by diffusion more efficient.
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Figure 8.17d
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Figure 8.17e
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Nervous systems
• All fish have a central nervous system.
• Highly developed sense of smell- olfactory sacs on both sides of the head.
• Taste buds- some have them on the fins and skin. Bottom dwellers have ‘whiskers’.
• Lateral line system- allows fish to detect vibrations in the water.
• Chondrichthyes- ampullae of Lorenzinican detect weak electrical fields for locating prey.
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Lateral Line system
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Behavior
• Territoriality- when an animal establishes and defends a particular area.
• Territories can be:
• Only during reproduction.
• Permanent- for feeding and shelter.
• Most common in crowded environments.
• Ex.- Damselfish.
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Aggressive behavior
• Used to defend territories or mating rights.
• Fighting is rare, bluffing is common.
• Open mouths, raised fins, rapidly darting at another.
• Some use sounds, like rubbing bones or fin spines together.
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Schooling- herring, sardines, mackerel, few sharks and rays.
• Well coordinated, but have no clear leaders.
• Use vision, lateral line, olifaction, and sound to remain in perfect unison.
• Why do fish school?
• Confuse predators by circling or dividing.
• Increase swimming efficiency.
• Advantages in feeding and mating.
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Traveling schooling pattern
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Plankton feedingschooling pattern
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Encirclement of predator- schooling pattern
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Streaming- schooling pattern to avoid predation
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Migration- mass movements from one place to another.
• Migration can be daily, yearly, or once in a lifetime.
• Migration can be from offshore to intertidal, up and down the water column, to transoceanic.
• Mostly related to feeding and reproduction.
• Ex.- Open water fish like tuna migrate for feeding purposes.
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Migration for reproduction
• Anadromous fishes- Spend adult lives at sea, but migrate to fresh water for spawning.
• Salmon- once entering streams to reproduce, they do not feed, and their kidneys must adjust to fresh water.
• Homing behavior- salmon use chemical memory of their home stream and the streams they pass to find their spawning ground.
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Figure 8.22
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Migration for reproduction (cont’d)
• Catadromous fishes- Live in fresh water and return to sea for breeding.
• Freshwater eels- live in freshwater and migrate to the Sargasso Sea to spawn.
• Their larvae drift for a year before metamorphosis into adults.
• Possibly use magnetic field and currents for locating spawning grounds.
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Figure 8.24
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Reproduction
• Sexes are usually separate. (not always)
• Hermaphrodism-most common in deepsea fishes that rarely encounter another of their own species.
• Sex reversal- Begin life as one sex but change during life cycle.
• ex- sea basses, groupers, parrotfishes
• Anemonefish- all begin as males, one female develops. If she dies, the next largest male becomes female.
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Reproductive behavior
• Migration to breeding grounds.
• Color changes in bony fishes- salmon eyes turn bright red. Changes in chromatophores can cause skin changes.
• Behaviors- Postures, fin displays and swimming pattern to attract mates.
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Fertilization
• External fertilization- (broadcast spawning).
Many eggs are produced, can float as plankton or be deposited on the bottom. Most do not survive.
• Internal fertilization- used mainly by cartilaginous fish.
• Oviparous- Egg-laying. Most fishes.
• Ovoviviparous- eggs held within the mothers body until hatching- mostly cartilaginous fish.
• Viviparous- birth to live young that are nourished by the mother- a few sharks.
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Figure 8.28
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