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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?