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MARINE FISHES
Chapter Outline
FISHES AND OTHER VERTEBRATES
JAWLESS FISHES
Hagfish
Lampreys
CARTILAGINOUS FISHES
Sharks
Body Shape
Fish Coloration and Patterning
Locomotion
Respiration and Osmoregulation
Cardiovascular System
Feeding in Fishes
Adaptations to Extreme Cold
Adaptations to Avoid Predation
Reproduction
Oviparity
Ovoviviparity
Bearers
Hermaphroditism
Larval Development
Schooling
Fish Migrations
Chapter Objectives
• Describe the anatomy and physiology of the jawless fishes.
• Describe the anatomy and physiology of the cartilaginous fishes.
• Identify the adaptations of the sharks, skates, rays, and chimaeras.
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Key Terms
vertebrae
anadromous
ammocoetes
zooplanktivorous
caudal fin
chromatophores
iridophores
obliterative
countershading
poster colors
neuromasts
otoliths
maculae
nictitating membrane
spiral valve
Chapter Summary
1. Marine adaptation—surviving in near-freezing water.
2. Hagfishes and lampreys are the only existing representatives of early jawless fishes.
Hagfishes are bottom-dwelling predators of soft-bodied invertebrates and
3. Sharks, skates, rays, and chimaeras are the modern representatives of the
cartilaginous fishes, which comprise the class Chondrichthyes. Their skeletons are
composed almost entirely of cartilage, although it is often strengthened by
4. Chimaeras, or ratfish, have large pointed heads and long, slender tails. Unlike with
5. Bony fishes move about by drifting with the current, burrowing, crawling on the
bottom, gliding, and swimming—the latter being the most common method. Bony
fishes use their gills to extract oxygen from the water and eliminate carbon dioxide.
The cardiovascular system of fishes consists of a heart, arteries, veins, and
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Chapter Outline
I. Fishes and Other Vertebrates
A. Chordate characteristics.
1. Flexible notochord at some point in the life cycle.
B. Craniate: brain enclosed in cartilaginous or boney covering; evolutionary advance that
allowed these animals to become dominant marine and terrestrial life forms.
1. Except hagfish, all higher animals have boney and cartilaginous segments around the
spinal cord, providing protection and support.
II. Jawless Fishes
A. Cartilaginous skeletons.
B. Lack jaws and paired fins.
C. Hagfish: slime eels.
1. Widely distributed (except polar oceans) benthic fish.
2. Habitat.
3. Tanned hide used in production of leather goods.
4. Feeding behavior.
a. Dental plates.
D. Lampreys.
1. Anadromous: migrate from ocean to freshwater to spawn.
a. Males wait for females attached to rocks.
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III. Cartilaginous Fishes
A. Class Chondrichthyes: sharks, skates, rays, and chimeras.
E. Two groups.
1. Holocephalans: ratfish and chimeras.
2. Elasmobranches: sharks, skates, and rays.
F. Sharks.
1. Zooplanktivorous: animals that eat heterotrophic plankton.
2. Majority are carnivorous; top predators.
3. Spindle-shaped streamlined bodies.
9. Rows of teeth embedded in jaws; replaced as soon as they fall out from row of teeth
behind.
10. Lower jaw teeth serrated for tearing prey.
11. Temperate and tropical to depths of 200 m; majority of species inhabit waters of the
G. Skates and ray.
1. Flattened bodies with elongated pectoral fins used for swimming.
2. Reduced dorsal and ventral fins.
3. Spiracles: opening on dorsal body through which water enters and exits over the gills
6. Defense mechanism.
a. Electric rays have electric organs in head that can generate up to 220 volts.
b. Stingrays have pointed barb with venom; causes painful injury that is slow to
heal.
8. Mermaid’s purse: leathery skate egg case.
H. Chimeras: ratfish, rabbitfish, spookfish.
1. Large pointed head and elongated body.
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2. Cartilaginous skeleton.
3. Immovable upper jaw.
IV. Lobefin Fishes
A. Rod-shaped bones surrounded by thick muscles in pectoral and pelvic fins.
B. Two extant species, all from Indian Ocean.
C. Live in 150–250 m of water, steep lava slopes with caves.
V. Ray-Finned Fishes
A. 56% of 26,000 know species are marine; half of all vertebrates; 95% of all fishes are ray–
finned.
B. Swim bladder in most fish.
H. Two groups of ray-finned fishes.
1. Chondrostei: sturgeons.
a. Heterocercal tails.
I. Majority of commercially important fishes are ray-finned.
J. Used for human food, fertilizer, aquarium pets, pet food, and sport fishing.
VI. Fish Biology
A. Body shape adapted to habitat; refer to Figure 10–14.
1. Fusiform.
B. Coloration.
1. Chromatophores.
2. Obliterative countershading.
C. Swimming style.
1. Eels and other elongated fishes swim by undulating entire body in serpentine
movement.
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D. Respiration and osmoregulation.
1. Respiratory structures.
2. Gill structure.
a. Gill filaments.
3. Osmoregulation: maintenance of internal salt and water balance.
a. Most marine fishes loose water by osmosis because environment is saltier than
body fluids.
E. Cardiovascular system.
1. Two-chambered heart: atrium (top chamber) and ventricle (bottom chamber).
2. Sinus venosa.
F. Buoyancy regulation.
1. Sharks concentrate fatty substance, squalene, in their large livers to increase
buoyancy.
2. Swim bladder: gas-filled internal structure that can expand or contract to change
fish’s position in water column; some benthic species loose swim bladder as adults;
active swimming pelagic fishes lack swim bladders.
G. Nervous and sensory systems.
1. Olfactory receptors.
2. Barbels: “taste” receptors.
H. Digestion.
1. Mouth, pharynx, esophagus, stomach, and intestines.
2. Pyloric caeca: blind-end sacs that secrete digestive enzymes and increase surface area
6. Pancreatic tissue can be concentrated in one area or spread over the digestive system,
depending on the species.
I. Feeding.
1. Detritivores, omnivores, carnivores, and herbivores: fishes have a variety of prey.
2. Mouth shape related to food preference.
a. Puffer fish and boxfish crush their prey.
b. Butterfly fish use finely pointed mouth to feed on individual coral polyps.
passing over gills.
J. Adaptations to extreme cold.
K. Predator avoidance.
1. Camouflage.
2. Inflate body with air to increase size; e.g., puffers and burrfish.
3. Flying fish use pectoral fins to glide over the water, out of reach of predators.
7. Impact bubble—ciguatoxin.
L. Reproduction.
1. External or internal fertilization, depending on the species.
2. Dioecious, some sequential hermaphrodite species.
3. Oviparity.
4. Ovoviviparity.
5. Viviparity.
6. Reproductive strategies.
a. Pelagic spawners.
b. Benthic spawners.
N. Schooling.
O. Fish migration can be seasonal or diurnal.
1. Diurnal migration associated with feeding and/or predator avoidance.
2. Seasonal migration associated with spawning, environmental temperature change, or
food availability.
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Suggestions for Presenting the Material
1. Fish are highly variable animals, exhibiting a diversity of size, shape, and color
patterns. Fish have evolved to survive in all aquatic habitats. Fishes also have
2. The Discovery Channel’s 10-year anniversary Shark Week DVD collection includes
answers to questions on shark attack, shows footage outlining the life cycle of
varying shark species, and includes an episode on bull sharks.
3. The Blue Plant series contains wonderful footage of fishes in all the oceans (polar,
Classroom Discussion Ideas
1. Shark populations are declining worldwide, but their poor reputation has limited
public outcry. How would you propose changing that? Why do we need sharks?
Would it be acceptable to just protect the small sharks that are unlikely to attack
humans?
2. Explain the difference between countershading and disruptive coloration. Why
wouldn’t these protective adaptations work well for fish in the opposite
environment?
Videos, Animations, and Websites
Videos
Ancient Creature of the Deep. (PBS, Nova episode)
Documentary on coelacanths.
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Island of the Sharks. (PBS, Nova episode)
Documentary of Costa Rica’s Cocos Island, which has the largest shark population in the
world.
Sharks in Deep Trouble. (Documentary, 20 min)
Modern Marvels “Commercial Fishing.”
Ocean Oasis. (Documentary, San Diego Natural History Museum, 2001)
Websites
Florida Museum of Natural History Ichthyology Division.
This website has links to all sorts of information about fishes. It includes species
accounts, pictures, information on current research, and the International Shark Attack
The Fish Out of Time.
NOAA Fisheries, Office of Sustainable Fisheries.
Information on sharks.
Australian Museum.
This website has good information on marine fishes.
Suggested Answers to End of Chapter Questions
Multiple Choice
1. c. jaws
2. b. cartilage
3. d. placoid scales
Multiple Choice
1. g.
6. c.
11. m.
Short Answer
1. What are two adaptations that help prevent fish from sinking because of their
relatively high density?
Sharks sequester squalene (a low-density, fatty compound) in their livers to
2. Explain what is meant by “disruptive coloration” and give an example.
Disruptive coloration is a common color pattern in coral reef fishes such as the
3. Describe how a fish uses its trunk muscles to swim.
Fish swim by alternately contracting muscles on the opposite sides of the body,
4. What mechanism allows fish gills to extract up to 80 percent of the oxygen in the
water passing over them?
Gills—made from thousands of individual, thin gill filaments—have an extremely
5. How is the bull shark able to enter and live in freshwater?
6. Describe how reproduction in an oviparous fish differs from reproduction in an
ovoviviparous fish.
Oviparous fish reproduce by laying eggs that develop outside the mother’s body.
7. How do the swimming modes of skates and rays differ?
Rays swim by moving their fins up and down, while skates swim by creating a
8. Why do most carnivorous fishes swallow their prey whole?
Fish teeth are adapted for grasping prey, not for chewing. Furthermore, fish need
9. What special adaptations do crocodile icefish possess to compensate for their lack of
red blood cells?
10. Why is the blood pressure of fish lower than that of other vertebrates?
120 Marine Fishes
Thinking Critically
1. Jawfish and seahorses depend on the males to take care of their eggs. What is the
advantage of this reproductive strategy?
Male brooding of eggs frees the female fish to expend energy to produce another
2. What are some of the advantages of hermaphroditism as a reproductive strategy in
fish?
Hermaphroditism is a reproductive strategy that increases the opportunity for
3. What characteristics would you expect to observe in a fish that was adapted to a
sedentary life, hiding among rocks and coral on a coral reef?
Fishes that exhibit a more sedentary lifestyle such as the oyster toadfish (Opsanus
4. Several species of marine fish display different colors as juveniles and as adults. What
might be the benefit of this?
Many coral reef fishes that are sequential hermaphrodites exhibit multiple color
5. Why are crocodile icefish considered an “evolutionary dead end”?
The loss of the hemoglobin genes is not an advantage for survival in polar
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Suggested InfoTrac® Articles
“Ancient Swimmers.” Butler, C. National Geographic, (2011).