FISHES

Agnatha

Chondrichthyes

Osteichthyes

General Characteristics

Ectothermic Vertebrates Have scales Swim with fins Almost all exclusively aquatic Filter oxygen from water over gills

Classes of Fish

Agnatha – Jawless FishChondrichthyes –

Cartilagenous FishOsteichthyes – Bony Fish

Question #1:

What is the name for a person who studies fishes?

Ichthyologist

Early Fish

Earliest - Filter feeders, no jaws, no fins

Ostracoderms – jawless, heavy bony plates

Lobe finned fishes – Coelocanths

Fish Anatomy

Fins

Caudal – propels fish forward Dorsal – stabilizer Anal – stabilizer Pectoral – hold fish steady, maneuvering Pelvic – hold fish steady, maneuvering

Scale Types

Cycloid – smooth surface, on bony fish – Carp– Salmon

Ctenoid – teeth along ridge (rough to touch), on bony fish– Bass– Bluegill– Perch

Scale Types

Placoid – Look like tiny teeth, feel like sandpaper, on cartilagenous fish– Sharks– Rays

Ganoid – hard, interlocking, diamond-shaped, on primitive fish– Gar

Question #2:

What is the purpose of a fish’s scales? Shield against injury, help to move through the

water

Maintaining Buoyancy

Swim bladder – Uses air– Most bony fishes– Can be used as a second “lung”

Liver– Uses oil– Sharks– Most sharks must constantly swim to avoid

sinking

Locomotion

Use fins and body wall to push against water

Forked tails reduce drag in the waterMuscles in a zig-zag shape

– Each contraction moves large parts of the body wall

Gills

Obtain oxygen Give off carbon dioxide Most have an operculum Oxygen dropped into circulatory system

pumped by 2-chambered heart

Gas Exchange

Pump ventilationRam ventilationExchange of gases occurs in capillary

network in gill lamellae; water and blood flow in opposite directions over lamellae = Countercurrent Exchange

Countercurrent Exchange System

Excretion and Osmoregulation

Freshwater fishes – never drink– Lots of

nephrons– Ions are

reabsorbed

Marine fishes– Drink constantly– Less blood is

filtered– Water is

reabsorbed

Senses

Limited vision, focus by moving lens back and forth

Olfactory receptorsMagnetic receptorsTouch

Sense (cont.)

Hearing – sound conducted through skull

Lateral line system – senses movement of other organisms around them

Electroreception – sense electrical impulses generated by muscle twitches

Reproduction

Oviparous (most fish)– Release eggs, young develop outside mom

Ovoviviparous (some cartilaginous fishes)– Eggs remain inside mom– Eggs at a later stage of development before they

are released

Viviparous (a few sharks)– Young born alive

Class Agnatha

CartilagenousSimplest and oldest vertebratesJawlessNo scalesScavengers or parasitesLamprey, hagfish

Class Chondrichthyes

Hinged jawPaired finsScalesMuscles attached to skin, not

skeletonCartilagenous skeleton

Sharks

Jaws not attached to brain case– Can protrude during attack– 20 tons per square inch for an 8’ shark

Size varies (few inches to over 40 feet)

Variable body shapes

Skates and Rays

Wing-like pectoralsMost live on sea bedsSome have poison spines on backs

or tails (stingrays)

Class Osteichthyes

Largest group of fishesSkeleton made of bone and cartilageHinged jawsPaired finsHard, protective scalesCovered gills (operculum)

Major Groups of Osteichthyes

Subclass Sarcopterygii– Lobe-finned fishes (Coelocanth)– Lungfishes

Subclass Actinopterygii – – Ray-finned fishes

BassTunaGuppies