Fish

Class Agnatha, Chondrichthyes, &

Osteichthyes

Subphylum Vertebrata

● All vertebrates are divided into two Superclasses

● Superclass Agnatha - Jawless vertebrates (2 living species)

● Superclass Gnathostomata - Jawed vertebrates (all other vertebrates)

Vertebrate Reproduction

● Oviparous ○ Lay eggs outside the body

so they may develop and hatch

● Ovoviviparous○ Egg remains in mother until

offspring hatch○ The offspring are born alive

● Viviparous○ Embryo receives

nourishment from mother○ The offspring are born alive

Placoderms

Ostracoderms

Hagfish & Lampreys

Cartilaginous Fish Bony Fish

Lobe-Finned Fish

Ray-Finned Fish

Coelacanths

LungfishEarly Amphibian

(Ancestor of all Tetrapods)

Superclass Agnatha● First appeared in the Cambrian

Period about 500 mya

● No jaws

● No paired appendages

● Notochord provides primary protection and support for nerve cord

● Fertilization & development are carried out externally

Ostracoderms

● Earliest vertebrates

● Evolved just after the Cambrian explosion

● Jawless - fed by filter feeding

● Covered in armor made of bony plates

● Totally extinct group of fish (P-T extinction)

Hagfish and Lampreys

Lampreys

● Live mostly in coastal and fresh waters

● Always return to freshwater to reproduce

● Though jawless, the mouth is lined with sharp teeth able to tear flesh

● Ectoparasitic

Lampreys

● Begin life as burrowing, toothless larvae

● After 5 to 7 years, they undergo an incredible metamorphosis to turn into pelagic, adult parasites

● Attach to fish, secrete an anticoagulant, and feed on blood

Hagfish● Jaw is partially movable

horizontally, but still considered Agnathans

● Entirely marine - never found in freshwater

● Able to change sex to meet population needs - many species exist in a 100:1 female-to-male ratio

● No larval stage

Hagfish

● Able to secrete copious amounts of thick slime to deter or evade predation

● Clean off the slime by tying themselves in knots

● Endoparasites - feed by burrowing into the mouth, gills, or anus of a host fish and consuming their prey from the inside out

Superclass Gnathostomata

● Jaws● Paired appendages

Placoderms

Ostracoderms

Hagfish & Lampreys

Cartilaginous Fish Bony Fish

Lobe-Finned Fish

Ray-Finned Fish

Coelacanths

LungfishEarly Amphibian

(Ancestor of all Tetrapods)

Class Placodermi

● Among the first jawed fish along with the ancestors of Class Chondrichthyes

● Went extinct along with the Ostracoderms

● Head and thorax were covered by bony plates

● 320 mya fossil shows earliest example of viviparous birth

Class Chondrichthyes

● Cartilaginous skeleton

● Notochord provides a large portion of back support

● No operculum○ Must swim constantly

to allow oxygenated water to move across gills

● No swim bladder ○ They are unable to

regulate their buoyancy levels

Buoyancy

● Cartilaginous fish must also constantly swim to keep from sinking. They use dynamic lift to maintain a constant level in the water column

● Liver oil and the ability of some sharks to swallow air allow them to obtain some level of buoyancy

Class Chondrichthyes● Respire with the use of 5 to

7 exposed gill slits

● Skin covered with dermal denticles - tooth-like structures that protect the skin and cause it to feel like sandpaper when rubbed against the grain

● Denticles also reduce small vortices produced during movement that cause hydrodynamic drag - increase swimming efficiency

Sharks

● The largest of all fish is the whale shark. It is a filter feeder

● Most sharks are simple carnivores

● Teeth are anchored into flesh rather than bone and they rip out and are replaced very rapidly

Shark Anatomy

Sexual Dimorphism in Sharks

Sharks

● Although most fish are exothermic, the shortfin mako shark and the great white shark are slightly endothermic

● Most sharks are ovoviviparous. They carry their eggs internally until the young hatch and are born alive and fully functional

Sharks

● Sharks have electroreceptor organs called the Ampullae of Lorenzini that detect the electromagnetic fields that all living things produce. This assists sharks in hunting and in navigation

● Sharks also have a very keen sense of smell and can detect 1:1,000,000 blood in water

Skates & Rays

Skates & Rays● Possess 5 gill slits that are

located underneath the pectoral fins rather than on the side of the head as in sharks

● Eggs laid in little pouches you may find on the beach

Skates & Rays● Wide distribution of group

members. Tropical to cold-water species exist

● Most are benthic (live on the seafloor) and respire by moving water in through their spiracles towards their gills

● Manta ray is an example of a rare pelagic ray

Skates & Rays·Skates and rays are very similar. However, skates tend to have a

more shovel-shaped head than rays and they lack spines in their tails.

Placoderms

Ostracoderms

Hagfish & Lampreys

Cartilaginous Fish Bony Fish

Lobe-Finned Fish

Ray-Finned Fish

Coelacanths

LungfishEarly Amphibian

(Ancestor of all Tetrapods)

Class Osteichthyes

● Boney fish - Actually called endochondral bone because it is formed by the ossification of cartilage

● Comprise the most various and largest class of vertebrates on Earth today

● Includes the vast majority of all

fish

Class Osteichthyes

● Swim bladder present - Allows a fish to adjust its buoyancy and thus its position in the water column

● Operculum present - Allows fish to pump water across the gills without having to physically move through the water

● Lateral line – senses vibrations in the water

Oxygen Exchange at the Gills

Countercurrent Exchange

Osteichthyes Evolution

Osteichthyes Classification

Subclass Actinopterygii

● Ray-finned fish

● Comprised of most members of class Osteichthyes

● Fins attach to body of the fish with multiple, small bones

● All members have homocercal tails

Caudal Fins

General Osteichthyes Anatomy

Subclass Actinopterygii

● Bichirs

● Also known as ropefish

● Live in freshwater environments in Africa and around the Nile delta

● Identified by noting the unique 12+ dorsal fins

● Sister group of all other ray-finned fish

● Sturgeon & Paddlefish

● The most ancient living bony fish with shark-like heterocercal tails & partially cartilaginous skeletons

● Sturgeons lack normal scales seen on other bony fish but they have armor plates along their sides

● Paddlefish lack the armor plating but have paddle-like rostrums the detect electromagnetic fields

Subclass Actinopterygii

Subclass Actinopterygii● Gar

● Fresh, brackish, & marine fish of the Americas

● Almost as old and primitive as the sturgeons & paddlefish

● Thicker scales than other bony fish but not as heavily armored as the sturgeons

● Identifiable by noting the long, skinny snout

Subclass Actinopterygii● Bowfin

● Only a single surviving species in this entire family of fish is native to eastern US & Canada

● Closest relative to the teleost fish

● Known for their long dorsal fins that cover most of their back

● Considered a trash fish - not very edible

Subclass Actinopterygii

● Teleost Fish

● The most advanced of all fish

● Almost 30,000 species - more than all other vertebrate species combined

● Almost any fish you can name belongs to this group

● Extremely important as food sources for humans and many other animals

Subclass Sarcopterygii

● Lobed fins joined to the body at a single bone

● Two dorsal fins with separate bases and diphycercal caudal fins

● There are only 8 living species in this subclass

●● These include lungfish and

coelacanths

Subclass Sarcopterygii

● Sauropterygians are able to utilize a primitive lung to breathe air when their ponds dry out or the water becomes anoxic

● Lungfish are known to use their fleshy pectoral fins like legs and crawl to new ponds when their previous ponds dry out

Structure of Lungs

● The Trachea leads down to the lung

● Separates into two bronchi leading to each lung

● Tubing terminates into little sacks called ALVEOLI that allow for gas exchange

Subclass Sarcopterygii

● ·The subclass split into two main groups long ago with the coelacanths staying in the ocean and the lungfish & tetrapodomorphs moving to freshwater environments

● Tetrapodomorphs further evolved into land vertebrates

Fish Scales

The End!