Marine Fishes

Chapter 8

Vertebrates• Share characteristics with protochordates

(invert chordates)– Single, hollow nerve cord– Pharyngeal slits– Notochord (between nerve cord and gut)– Post-anal tail

• Different because they have a vertebral column (spine)– Protects nerve chord– Bilateral symmetry

Types of Fishes

• Oldest and simplest vertebrates• Most abundant

– About half of species– 15,300 marine

• 3 major groups– Agnatha (jawless fishes)– Chondrichthyes (cartilaginous fishes)– Osteichthyes (bony fishes)

Jawless Fishes (Class Agnatha)

• Lack jaw – Feed by suction with a round mouth and rows

of teeth• Body is cylindrical and

elongated• Lack paired fins and

scales• Lack true vertebrae

Classes of Jawless FishHagfishes

• AKA slime eels– Produce slimy mucus

• Feed on dead or dying fish• Live in burrows in cold

water• ~20 species known

Lampreys• Found in temperate regions• Breed in freshwater; marine

as adults• Attach to other fish and suck

on blood• ~30 species known

Eww… slime

Cartilaginous Fishes (Class Chondrichthyes)

• Skeleton made of cartilage• Movable jaws with teeth• Paired lateral fins• Rough, sandpaper-like skin

– Placoid scales: pointed tip directed backward• Sharks, rays, skates, and ratfishes

Shark Body• Adapted for fast swimming

and predatory feeding• Fusiform: spindle-shaped

body• Caudal fin: tail fin;

powerful– Heterocercal: upper lobe

longer than lower

• 2 Dorsal fins

• Paired pectoral fins– Large and pointed

• 5-7 gill slits• Rows of sharp,

triangular teeth– Rows are replaced

with back row

Exceptions to the Rules

• ~ 350 living species• Hammerhead

– Wide head; improves sensory perception• Sawshark

– Long, flattened blade armed with teeth• Spined pygmy shark

– Only 10 in long• Whale Shark (largest fish)

– Up to 60 ft long; over 40 ft is rare– Filter feeders (plankton), not hunters

Planet Earth Great White Attack

Manta Rays and Whale Shark

Rays and Skates

• 450 – 550 species• Dorsoventrally flattened bodies• Demersal: live on the bottom• Gill slits underneath (5)• Eyes on the top of head• Sawfish

– Ventral slits so they are grouped with rays

Stingrays

Stingrays• Whip-like tail with spines• Poison glands • Feed on clams, crabs,

fish, animals in sediment• Damage shellfish beds• Teeth are modified

grinding plates

Electric Rays• Special organs that

produce electricity on each side of head

• Shocks up to 200 volts

Manta Rays

• Fly through water• Feed at bottom

or midwater• Largest Manta =

23 ft

Skates

• Similar in appearance and feeding• Lack spines and whip-like tail• Some have electric organs• Lay egg cases

– Rays give birth to live young

Ratfishes• Chimaeras• Mostly deep-water & strange-looking• One pair of gill slits covered with skin• Rat-like tail• Feed on crustaceans

and molluscs

Bony Fishes (Osteichthyes)

• ~23,000 species– 96% of all fishes– ½ of all vertebrates– More than ½ live in the ocean

Skeleton Composition• Skeleton of some bone• Cycloid or ctenoid scales:

thin, flexible, and overlapping– Cycloid: smooth– Ctenoid: tiny spines along borders– Scales made of bone and covered with skin

and mucus– Some do not have bones

• Operculum: flap of bony plates that protects gills

Fins

• Homocercal: lobes of caudal fin are the same size– Sharks are heterocercal

• Fin rays consist of membranes supported by bony spines – Act as rudders or used as protection– Added maneuverability– Sharks have stiff, fleshy fins

Mouths

• Mouth is terminal (anterior end)– Cartilaginous have

ventral mouths• Jaws are protrusible• More freedom of

movement• Teeth can be replaced

but are not in rows

Buoyancy

• Swim bladder: gas-filled sac to adjust buoyancy– Cartilaginous fish have oily livers