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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 Fish Lecture related to swimming. • Discuss the reason some fish go to school.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vertebrate Features Oral hood with tentacles Notochord

Phylum Chordata Dorsal nerve cord • 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: Pharynx • Notochord —dorsal rod-like structure that serves as an Muscle blocks embryonic skeleton Pharyngeal slits • Pharyngeal gill slits • Dorsal hollow nerve cord —a tube that runs beneath the dorsal surface above the notocord Intestine • Post-anal tail Anus • Bilateral symmetry • Segmented body , including segmented muscles Postanal tail 4

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Vertebrate Features Fish General Features

• All chordates with a vertebral column are in the • Extremely diverse in form and function subphylum Vertebrata. • Most basic description of a fish—live in water, swim with fins, • Vertebral column replaces the notochord. and use gills for oxygen and CO 2 exchange. • May be made of cartilage or bone. • Have a single loop closed circulatory system – with Heart. • Those that do not have vertebrae are invertebrates. • Very prehistoric—fossil record goes way back! • Invertebrate chordates have all of the chordate features Conodonts – discovered in 1983 from Cambrian. at some point in life…………………just no vertebrae.  Why do fish fossilize well?
Lancelets
Tunicates (sea squirts) Three classes of fishes- vary greatly. 1) Agnatha - jawless 2) Chondrichthyes - cartilagenous 3) Osteichthyes – bony (aka Teleost) https://www.seeker.com/photos-the-surprising-world-of-sea- squirts-1768678963.html

I. Agnatha: The Jawless Fishes II. Chondrichthyes:

• Very different from other fish classes Sharks, Rays, Chimaeras • Only two orders exist: lampreys and • Almost all marine, a few notable exceptions hagfish e.g. Sharks in Lake Nicaragua • Very primitive and simple https://www.animalanswers.co.uk/animals/how-do- hagfish-defend-themselves/ • Larger in body size than other fish classes • Slender, eel-shaped body • Largest living animals besides whales • Seven external gill openings • Range from <20 cm to 15 m long – whale sharks • Notochord persists in the adult. • Skeleton composed of cartilage • Lack many fish-like features • Salts in body are less than seawater, so must maintain osmotic balance. • No paired fins • No biting jaws • Accumulate high concentrations of urea to aid in salt • No scales balance Isotonic with water • Able to maintain an internal ion concentration equal to that Detritivores live in burrows. outside the body (in seawater) Direct development from eggs. Renown for slime.

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II. Chondrichthyes: Sharks 7.3 Chondrichthyes: Rays

Sharks Rays – Batoid fish • Almost all are fierce predators. • Spines used for defense • Few are filter feeders (e.g. • Some are poisonous, whale shark). others sharp and painful. • Adapted for speed, maneuverability, and strength • Used for defense only, • Teeth are modified scales. not to capture prey • Numerous rows of teeth attached Example: stingray at their bases by connective • Countershading tissue • Several rows of replacement • Swim with pectoral fins teeth continually develop behind • Gill slits on ventral/belly side the outer rows of functional teeth • Eat a variety of food including mollusks, fish. (c) cbpix/Shutterstock https://www.aquariumdomain.com/adSocial/index.php/nurse-shark/ • Manta rays - planktivorous © Matt9122/Shutterstock

7.3 Chondrichthyes: Chimaeras Chondrichthyes Fish Reproduction Chimaeras (a.k.a. ratfish, elephant fish, rabbit fish) • In Greek mythology, chimaera is a monster. • Oviparous —lay eggs/spawn with no support to young • Very few species and rare in the world’s oceans unless they lay a nest and tend to it e.g. rays • Have long, rat-like tails • Viviparous —live bearers; the ultimate support to • Glide through the water with large pectoral fins extended young. E.g. Hammerhead sharks • Very different look from all other fish • Ovoviparous —store eggs in body, but do not provide • Skin is smooth & without any other nutritional support; support developing young scales. e.g. Mako shark • Primarily forage on invertz on floor of sea. • Young called a “pup”

http://galleries.neaq.org/2011/06/just- biofacts-shark-egg-cases.html

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Osteichthyes – Bony fish Yellow-tail Snapper

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

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 height 2) / fin area • Higher aspect ratio is ideal for fast, long-distance swimming.

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A remarkable fish Schooling Behavior

• Opah Fish schools vary in size few – innumerable (over several sq kms) • A unique and fully endothermic fish Usually all of the same species. • Specialized gills to warm the blood Safety in numbers approach. May confuse potential predator • Spend time in cold, deep water Spatial arrangement • The only nonmammal or > Visual cues bird species to exhibit > Vibrational cues full endothermy Broadcast spawning – reproductive advantage Can you think of any disadvantages?

NOAA/SWFSC

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