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 Fish Hagfishes 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 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