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5/29/2018
1
Fish Lecture
Student Learning Outcomes
• Define “vertebrate” and list their features.
• Make comparisons between agnathans and jawed fishes.
• Discuss the main features of chondrichthyans.
• Describe and compare three osteichthyes orders.
• Understand different aspects of fish adaptations related to swimming.
• Discuss the reason some fish go to school.
Vertebrate Features
Phylum Chordata
• Includes fishes, amphibians, reptiles, birds and mammals. Several invertebrates also in this group e.g. Sea squirts
During some phase of their lives, all Chordates have:
• Notochord—dorsal rod-like structure that serves as an embryonic skeleton
• Pharyngeal gill slits
• Dorsal hollow nerve cord—a tube that runs beneath the dorsal surface above the notocord
• Post-anal tail
• Bilateral symmetry
• Segmented body, including segmented muscles4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Oral hood with tentacles
Notochord
Dorsal nerve cord
Muscle blocks
Postanal tail
Pharynx
Pharyngeal slits
Intestine
Anus
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Vertebrate Features
• All chordates with a vertebral column are in the
subphylum Vertebrata.
• Vertebral column replaces the notochord.
• May be made of cartilage or bone.
• Those that do not have vertebrae are invertebrates.
• Invertebrate chordates have all of the chordate features
at some point in life…………………just no vertebrae.
�Lancelets
�Tunicates (sea squirts)
https://www.seeker.com/photos-the-surprising-world-of-sea-
squirts-1768678963.html
Fish General Features
• Extremely diverse in form and function
• Most basic description of a fish—live in water, swim with fins, and use gills for oxygen and CO2 exchange.
• Have a single loop closed circulatory system – with Heart.
• Very prehistoric—fossil record goes way back!
Conodonts – discovered in 1983 from Cambrian.
� Why do fish fossilize well?
Three classes of fishes- vary greatly.
1) Agnatha - jawless
2) Chondrichthyes - cartilagenous
3) Osteichthyes – bony (aka Teleost)
I. Agnatha: The Jawless Fishes• Very different from other fish classes
• Only two orders exist: lampreys and
hagfish
• Very primitive and simple
• Slender, eel-shaped body
• Seven external gill openings
• Notochord persists in the adult.
• Skeleton composed of cartilage
• Lack many fish-like features
• No paired fins
• No biting jaws
• No scalesIsotonic with water
Detritivores live in burrows.
Direct development from eggs.
Renown for slime.
https://www.animalanswers.co.uk/animals/how-do-
hagfish-defend-themselves/
II. Chondrichthyes:Sharks, Rays, Chimaeras• Almost all marine, a few notable exceptions
e.g. Sharks in Lake Nicaragua
• Larger in body size than other fish classes
• Largest living animals besides whales
• Range from <20 cm to 15 m long – whale sharks
• Salts in body are less than seawater, so must maintain
osmotic balance.
• Accumulate high concentrations of urea to aid in salt
balance
• Able to maintain an internal ion concentration equal to that outside the body (in seawater)
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II. Chondrichthyes: Sharks
Sharks
• Almost all are fierce predators.
• Few are filter feeders (e.g. whale shark).
• Adapted for speed, maneuverability, and strength
• Teeth are modified scales.
• Numerous rows of teeth attached
at their bases by connective tissue
• Several rows of replacement
teeth continually develop behind
the outer rows of functional teeth
(c) cbpix/Shutterstock
https://www.aquariumdomain.com/adSocial/index.php/nurse-shark/
7.3 Chondrichthyes: Rays
Rays – Batoid fish
• Spines used for defense
• Some are poisonous,
others sharp and painful.
• Used for defense only,
not to capture prey
Example: stingray
• Countershading
• Swim with pectoral fins
• Gill slits on ventral/belly side
• Eat a variety of food including mollusks, fish.
• Manta rays - planktivorous © Matt9122/Shutterstock
7.3 Chondrichthyes: Chimaeras
Chimaeras (a.k.a. ratfish, elephant fish, rabbit fish)
• In Greek mythology, chimaera is a monster.
• Very few species and rare in the world’s oceans
• Have long, rat-like tails
• Glide through the water with large pectoral fins extended
• Very different look from all other fish
• Skin is smooth & without
scales.
• Primarily forage on invertz
on floor of sea.
ChondrichthyesFish Reproduction
• Oviparous—lay eggs/spawn with no support to young
unless they lay a nest and tend to it e.g. rays
• Viviparous—live bearers; the ultimate support to
young. E.g. Hammerhead sharks
• Ovoviparous—store eggs in body, but do not provide
any other nutritional support; support developing young
e.g. Mako shark
• Young called a “pup”
http://galleries.neaq.org/2011/06/just-
biofacts-shark-egg-cases.html
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Osteichthyes – Bony fish
The most abundant ray-finned fishes are the group
Teleostei - Class: Actinoptergygii
• In the ocean there are 26 orders, hundreds of
families, and thousands of species.
• Traits
• Bony skeletons (calcified)
• Thin and flexible scales
• A gas-filled organ (swim bladder)
• Low concentrations of salt in the body
Yellow-tail Snapper
Seahorse Mola - Sunfish
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Circulation in Fish The art of swimming
Mechanism: pressure of fish fins against water is used to
swim through water.
• Muscles/myomeres contract and relax forming a wave-like motion.
I. Most fish are generalist swimmers.
II. Some fish are specialized swimmers, influenced by food choice,
habitat, and lifestyle.
• Barracuda sprints (ambush predator). Long body - bursting
• Butterfly fish finely maneuver (hover and pick off small prey items).
• Tuna cruise at high speeds to find prey (transit large areas).
Tuna torpedo-shaped & thick with muscles for long endurance swimming
Body Shape Specialization Caudal fin – provides a clue
Tail (caudal fin) shape
• Determines amount of forward thrust
• Can be measured by the aspect ratio = (fin height2) / fin area
• Higher aspect ratio is ideal for fast, long-distance swimming.
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A remarkable fish
• Opah
• A unique and fully endothermic fish
• Specialized gills to warm the blood
• Spend time in cold, deep water
• The only nonmammal or
bird species to exhibit
full endothermy
NOAA/SWFSC
Schooling Behavior
Fish schools vary in size few – innumerable (over several sq kms)
Usually all of the same species.
Safety in numbers approach. May confuse potential predator
Spatial arrangement
> Visual cues
> Vibrational cues
Broadcast spawning –
reproductive advantage
Can you think of
any disadvantages?