Marine Fishes Read Chapter 9 Pages

Chordates  All chordates have (at least during some period of their life) –Dorsal nerve cord –Gill slits –Notochord –Post-anal tail  These are the 4 basic characteristics of all chordates.

Bridging the gap Chordates w/o backbone  Tunicates –Not fish but chordates  Lancelets: Not a Vertebrate, but a Chordate –Chordate characteristics throughout life- –But no backbone –Subphylum Cephalochordata

The Fishes Note: The term fish refers to a single fish or a group of the same species of fish. Fishes refer to more than one species of fish.

Fish  Structurally simplest living vertebrates  Probably ~30,000 species  At least half of all known vertebrate species are fishes  At least half of all known fishes are marine  First appeared about 500 million years ago and were the first vertebrates –every other vertebrate has ultimately descended from a fish-like ancestor

Three major groups of Fish  Jawless fishes (Agnatha)  Cartilaginous fishes (Chondrichthyes) –Sharks and rays (elasmobranchs) –Ratfishes (chimeras) (Holocephalins)  Bony fishes (Osteichthyes) –Lobe-finned fishes –Ray-finned fishes

Jawless Fishes  Most primitive living fishes  Feed by suction with a round, muscular mouth and rows of teeth  Long, cylindrical body  No paired fins or scales  Lampreys are parasites on other fishes and suck on their blood; hagfish typically feed on dead animals

Jawless Fish

Cartilaginous Fishes  Sharks, rays, skates, chimeras (ratfishes) –Skeleton is made of cartilage, which is lighter and more flexible than bone –Moveable jaws with well-developed teeth –Paired lateral fins for efficient swimming –Rough skin due to placoidscales

Sharks  In some form, sharks have been around for about 400 million years.  Even before dinosaurs roamed the earth, sharks hunted through the oceans! They're such good survivors that they've had little need to evolve in the last 150 million years.  Scientific Information: Sharks belong to the class of fish, Chondrichthyes.  More on Sharks to come in a later lecture!!!

Skates vs. Rays  Skates –Oviparous (lay eggs)  Mermaids purse –Do not have barbs, have thorns on their dorsal area or tails  Placement and number vary –Small teeth  Rays –Viviparous (bare Live young) –Have Barbs  Above tail –In general, larger  Tail almost 2x’s as long as body –Plate Like Teeth

Skates and Rays  Flattened body  Large pectoral fins

Rat Fishes (Chimeras)  Bizarre-looking, primarily deep-sea, cartilaginous fishes  Have only one pair of gill slits instead of 5-7  Have a long rat-like tail  Feed on crustaceans and molluscs

Cartilaginous vs. Bony Fish Cartilaginous  skeleton made of cartilage  possess movable jaws mostly with powerful teeth.  mouth is located ventrally (under the head).  presence of paired lateral fins allows for efficient swimming.  skin is covered with small scales that have the same composition as teeth. Bony  Skeleton made (at least partially) of bone  Thin, flexible, overlapping scales along the body  A flap of bony plates and tissue known as the gill cover, or operculum, that protects the gills  Protruding jaws with more freedom of movement than cartilaginous fish  The presence of a swim bladder –helps buoyancy and compensates for the relatively heavier bony skeleton  Highly maneuverable fins

Cartilaginous Vs. Bony – External

Cartilaginous vs. Bony

Extinct No More  Subclass Sarcopterygii-Once known only for fossils and thought to be extinct for 60 million years-Named Latimeriachalumnae  Preserved specimen of the Coelacanth is located in the HMNH

Next Up Fish Form and Function