Chapter 10
Key Concepts
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Hagfishes and lampreys are jawless fishes.
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Sharks, skates, and rays have skeletons composed entirely of cartilage.
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Sharks have streamlined bodies and highly developed senses.
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Most marine fishes have skeletons composed primarily of bone.
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The shape of a fish’s body is primarily determined by its environment.
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Color in fishes functions as camouflage, species recognition, and communication.
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Fishes move about by drifting, burrowing, crawling, gliding and swimming.
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Fish use their gills to extract oxygen from the water, to purge carbon dioxide and as
an aid in keeping proper salt level within the body.
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Sharks maintain neutral buoyancy
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Most ray-finned fish use a swim bladder to maintain neutral buoyancy.
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Fish have a lateral line system to detect water movement.
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Most fish are carnivorous but herbivores, omnivores, detritivores and filter feeders
also exist.
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While ray-finned fishes are typically oviparous, most cartilaginous fish are
ovoviviparous and bear live young.
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Fishes such as salmon and eels migrate long distances.
Fishes and Other Vertebrates
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Fishes are vertebrates
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Primitive fishes lacked paired fins and jaws
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Adaptation of jaws and paired fins allowed fish to more efficiently obtain food
Jawless Fishes
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Hagfish and Lampreys
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Lack both jaws and paired appendages
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Have skeletons of cartilage
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Lack scales
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Hagfish also lack vertebrae
Hagfishes
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Bottom dwelling “slime eels”
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Feeding apparatus of two dental plates
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Produce gelatinous fluid
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Little is known about reproduction.
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Both gonads present, but only one is functional.
Lampreys
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Have oral disk and rasping tongue covered with horny dentacles
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Reproduction
– Typically anadromous
– males migrate up rivers and build nests, female attaches to nest stone, male
attaches to back of female
– larvae (ammocoetes) are benthic filter feeders, after 3-7 years, they
metamorphose and return to the sea
Cartilaginous Fishes
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Sharks, skates, rays, chimaeras
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Skeleton of cartilage
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Possess jaws and paired fins
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Placoid scales cover skin
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2 major groups:
– holocephalans
– elasmobranchs (2 body forms)
Sharks
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Top predators
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Excellent swimmers
– heterocercal tail
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Males have claspers
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Ventral mouth with multiple rows of teeth
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Found in all oceans
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Humans exploit sharks for fins, meat, oil, leather, cartilage and sport
Skates and Rays
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Physically adapted to a bottom existence
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Enlarged pectoral
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Reduced dorsal and caudal fins
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Eyes and spiracles on top of the head
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Gill slits on the ventral side
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Lack anal fin
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Specialized teeth for crushing
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Electric rays have electric organs
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Stingrays have poisonous barbs
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Sawfishes and guitarfishes have a series of barbs
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Fished commercially for food, many are considered threatened
Chimaeras
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Ratfish, rabbitfish, spookfish
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Large pointed heads and long tails
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Gills covered by operculum
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Have flat plates for crushing prey
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Scales confined to a few dentacles
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No cloaca
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Males have claspers
Jawed Fishes
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Jawed fishes
– Most have paired fins and scales
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Two groups of jawed fishes
– Cartilaginous fishes have a skeleton of cartilage (example: sharks)
– Bony fishes have an embryonic skeleton of cartilage that is mostly
transformed to bone in adults; they have protective gill covers and moveable
fins
Two Lineages of Bony Fishes
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Ray-finned fish
– Include food fishes such as tuna and cod
– Fins are supported by thin rays derived from skin
– Gas filled swim bladder helps adjust buoyancy
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Lobe-finned fish
– Include coelacanths and lungfishes
– Have thick, fleshy fins with bony supports
– Have gills and lunglike sacs
Lobefins
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Coelacanths - now considered class Sarcopterygii
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Two extant species
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Only known as fossils until 1938
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Live deep in Indian Ocean
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Skeleton made of bone and cartilage
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Rostral organ
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Life span is 60 years
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Considered to be in danger of extinction
Ray-Finned Fishes
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2 major groups:
– subclass Chondrostei
• ganoid scales
– subclass Neopterygii
• homocercal tails
• cycloid & ctenoid scales
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Possess unpaired median fins and paired fins
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Median fins consist of 1 or more dorsal fins, caudal fin, and usually anal fin
– help maintain stability while swimming
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Paired fins consist of pectoral and pelvic fins
– both used in steering
– pectoral fins also help to stabilize the fish
The Biology of Fishes: Body Shape
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Shape of body determined by characteristics of habitat
Body Shape
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Laterally compressed or deep body
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allows navigation through
complex habitat, e.g., grass or corals
Fish Coloration and Patterning
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2 basic types of fish colors:
– Pigments
• chromatophores
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Structural colors
– iridophores
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Countershading
– obliterative countershading
– disruptive coloration
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Poster colors
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Cryptic coloration
Locomotion
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Trunk muscles propel the fish
– arranged in a series of muscle bands
– contract alternately from one side to the other
– contractions originate at the anterior end and move toward the tail
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Fish with different body forms swim in different ways
Respiration and Osmoregulation
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Gills often used to extract O2, eliminate CO2, and aid in salt balance
– gill filaments
– countercurrent multiplier system
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Water must be continuously moved past the gills to keep blood oxygenated
Buoyancy Regulation
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Maintaining buoyancy
– sharks sink if they stop swimming
– large livers produce squalene
– squalene helps maintain buoyancy
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Most fish use a swim bladder—a gas-filled sac that helps offset the density of the
body and regulates buoyancy
– the fish can adjust the amount of gas in the swim bladder to maintain depth
– gas is added as the fish descends and removed as it ascends
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2 methods for adjusting the amount of gas
– gulping air from the surface
– gas gland
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Active swimmers do not have swim bladders, and must swim to avoid sinking
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Bottom dwelling fish lack swim bladder
Nervous System and Senses
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Nervous system: brain, spinal cord, peripheral nerves, and various sensory receptors
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Olfaction and Taste
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olfactory receptors in sharks well developed
ray-finned fishes have olfactory pits
size varies with dependence of fish on olfaction
taste receptors may be located on the surface of the head, jaws, tongue,
mouth and barbels (whisker-like processes about the mouth)
Lateral line system and hearing
– ray-finned fishes have a lateral line system
– lateral lines consist of canals running along the length of the fish’s body and
over the head
– neuromasts
Vision
– no eyelids
– usually don’t need to adjust pupil size
– entire lens moves back and forth to focus
– eyes are usually set on the sides of the head
– most have monocular vision
– shallow-water species can perceive color
Digestion
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Pyloric caeca
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spiral valve
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All cartilaginous fish are carnivores
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Ray-finned fishes exploit all food resources
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Prey is swallowed whole
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Filter feeding fish use gill rakers
Adaptations to Avoid Predation
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Camouflage
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Inflated bodies to deter predators
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Flying fishes glide through the air
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Pearlfish hide in other organisms
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Parrotfish secrete a mucus cocoon
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Surgeonfish are armed with sharp spines
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Clingfishes attach to rocks so predators
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Triggerfish projects spines
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Scorpionfish and stonefish have venom
Reproduction
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Sexes are typically separate
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Sperm and eggs pass to the outside through ducts, except in salmon
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Egg and sperm development is usually seasonal
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Three reproductive modes:
– Oviparity
– Ovoviviparity
– Viviparity
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Pelagic spawners
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– release vast quantities
– fertilized eggs drift with the currents
– no parental care
Benthic spawners
– non-buoyant eggs with large yolks
– no parental care
– pelagic or benthic embryos/larvae
Brood hiders
Guarders
Bearers
Hermaphroditism
– synchronous
– sequential
• protogyny
• protandry
Larval Development
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Many larvae are zooplankton
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Initially nourished by a yolk sac
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Fishes grow for as long as they live
Schooling
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School of fish
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Shoaling
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Reasons for schooling:
increases food finding abilities
predators can’t focus on an individual
Fish Migrations
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Daily migrations
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Seasonal migrations
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Migrations may occur within seawater or between seawater and fresh water
– catadromous
– anadromous
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Freshwater eels
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Salmon
– Anadromous
– Pacific species die after spawning
– lay eggs in a redd
– salmon use odor to navigate upstream
– it is unknown exactly how they locate the correct river’s mouth