Download Ch. 30.2

Fishes
Ch. 30.2
 More than 2/3 of the Earth’s surface is water
 No matter where there is water, there is some sort of
fish living in the water
What is a Fish?
 Fishes are aquatic vertebrates that have pair fins,
scales, and gills
 However, there is a large variation between species
of fish
 Catfish don’t have scales
 One reason for variation is due to the many different
classes of fish
 (KPCOFGS)
Evolution of Fishes
 First vertebrates to evolve
 Probably evolved from common invertebrate
ancestors
 Evolution of jaws and pair fins were important
developments
The first fishes
 Jawless
 Bodies were armored with bony plates
 Late Cambrian period (~510 mya)
The Age of Fishes
 Between 505-410 mya, fishes underwent major
adaptive radiation.
 Species emerged were jawless with small amounts of
armor
 Ancestors of modern hagfish and lampreys
 Armored fish became extinct 360 mya
Arrival of Jaws and Paired Fins
 Jaws are a useful adaptation
 Jaws hold teeth and muscle and so food is more than
just small particles
 Eat a wider variety of foods
 Paired fins = pectoral and pelvic fins
 Give more body movement control
 Tail fins give more greater thrust in swimming
The Rise of Modern Fishes
 Divided into 2 groups:
 Cartilaginous fish (sharks and rays)
 Bony fish (other fish)
Form and Function in Fishes
 Evolved and adapted for:
 Various modes of feeding
 Specialized structures for gas exchange
 Paired fins for movement
 Fish have a variety of ways to feed (i.e. herbivores,
carnivores, parasites, filter feeders, etc).
 Some fish use multiple ways to eat in order to survive
 Digestion is somewhat complex (see diagram on
webpage)
 Gas exchange is via the gills
 Made of feathery, threadlike structures (filaments)
 The network provides for a large surface area
 Circulation – closed circulatory system
 Heart pumps blood in a single loop (heart  gills 
body  back to heart
 Excretion: rid nitrogenous waste as ammonia
 Some diffuse it through the gills, others have kidneys
 Response: fish have a well developed nervous system
 Cerebrum processes the sense of smell
 Cerebellum coordinates body movements
 Medulla oblongata controls the functioning of many
internal organs
 Have well developed eyes that see color
 Have strong sense of taste and smell
 Lateral line system helps a fish detect vibrations in the
water that help with sensing when prey are
swimming around
 Movement: alternate paired sets of muscles on either
side of their backbone (S shaped curve)
 Fins will help propel the fish forward
 Swim bladders are gas filled; help fish adjust their
buoyancy
 Reproduction: eggs are fertilized internally or
externally
 Oviparous – eggs hatched outside the body
 Ovoviviparous – eggs stay in the mother’s body and use
yolk for nourishment
 Viviparous – eggs stay in mother’s body and obtain
nourihment directly from the mother
 ONLINE PRACTICE ACTIVITY
 3 main classifications of fish:
 Jawless: no true teeth or jaws, made of cartilage, no
vertebrate, notochords as adults
 Lampreys, hagfish
 Condrichthyes (cartilaginous): skeletons made of
cartilage
 Sharks, rays, skates
 Osteichthyes (bony): skeletons made of bones; ray
finned (slender, bony spines)
 Lobed finned (fleshy fins)