The Fishes Vertebrate Success in Water Evolutionary Perspective

The Fishes Vertebrate Success in Water

Evolutionary Perspective • Primitive Fishes can be traced back 530 million years ago • Hagfish are the most primitive fishes known • Aquatic environments have selected for certain adaptations including streamlining for moving thru a dense medium • Ability to exchange gases with water or air • Regulating buoyancy and electrolytes and detecting environmental changes

Infraphylum Hyperotreti • Hagfish are divided into 20 species • Heads supported by cartilage bars and brains enclosed by a fibrous sheath • They lack vertebrae but retain a notochord as the axial supportive structure • Four pairs of sensory tentacles surround the mouth • Ventrolateral slime glands produce copious amounts of slime • They feed on invertebrates and dead fish

Hagfish

Hagfish Mouth

Hagfish Slime

Infraphylum Vertebrata • Ostracoderms are extinct agnathans • Sluggish swimmers, Had bony armor as their only defense • Bottom dwellers, filter feeders either filtering water or muddy sediment • Some ostracoderms used bony plates around the mouth as jaws to crack mollusc shells or arthropod exoskeletons

Ostracoderms

Lampreys • Agnathans (jawless) Fish who live in fresh and marine environments in temperate regions • Most adult lampreys prey on other fish, larva are filter feeders • Mouth is sucker like with lips used for attaching • Epidermal teeth line the mouth and tongue like structure • Attach to prey with teeth and lips, tongue rasps away scales • Anticoagulant produced in saliva, feeds on blood

Lamprey

Lamprey Mouth

Lamprey

Gnathstome, Jawed Vertebrates • Jaws evolved from the anterior pair of gill arches • Permitted more efficient gill ventilation • Allowed the capture and ingestion of more food sources • Streamlining and paired fins became more important with increased activity • Paired pectoral and pelvic fins reduced the tendency to roll during swimming

Class Chondricthyes • Cartilage skeleton fish, includes sharks, rays, skates and ratfishes (chimeras) • Most are carnivores and scavengers, most are marine • Placoid scales • Elasmobranch subclass (820 species) sharks, rays, skates started in early Devonian 375 mya • Tough skin with placoid scales pointing posteriorly aids in reducing friction

Chondricthyes

Basking Shark

Sting Ray

Manta Ray

Manta ray Jumping

Spotted Eagle Ray

Goblin Shark

Cookie Cutter Shark

Cookie Cutter Shark

Damage from Cookie Cutter Shark

Cookie Cutter Shark Bites

Hammer. Head

Skate

Great White

Rat Fish, Chimera

Spotted Rat fish, Chimera

Shark Feeding • Shark teeth are modified placoid scales • The row of teeth on the outer edge is backed up by rows of teeth attached to a ligamentous band • As the outer teeth wear or break off, they are replaced • Replacement is rapid, 7 -8 days • Teeth may be adapted for shearing flesh, Top teeth cut while bottom teeth hold • Teeth may be modified for breaking shells of molluscs

Placoid Scales

Shark Senses • Ampullae of Lorenzini- Sensory pits on snout of sharks, able to detect very small electrical charges, heart beating, nerve impulse • Lateral line- detects vibrations in the water, any movement or change in water pressure around the shark • Nostrils- widely spaced on both sides of head, nostril is u shaped, not used for breathing • Eye sight- Excellent, dark eyes to absorb maximum light, nictitating membrane cover

Ampullae of Lorenzini

Ampullae of Lorenzini Structure

Lateral Line

Lateral Line System

Nictitating Membrane

Rays, Skates and Ratfish • Rays and Skates are specialized for living on the ocean floor by expanding the pectoral fins • Some have venomous spine at base of tail used for defense • Many have camoflaged their dorsal surface to blend in with the bottom • Ratfish have a single gill cover (operculum) an enlarged head with teeth shaped for crushing shells

Sting Ray Barb

Osteichthyes Bony fish • 24, 000 species, all have at least some bone in their skeleton, Bony operculum covering their gill opening • First fossils 405 million years old, late silurian period • Class Sarcopterygii-two groups- lungfish and coelacanths • Lungfish have fleshy fins and gills and lungs • Coelacanth lobe finned fish, deep water

Coelacanth

Lungfish

Actinopterygii, Bony Fish • Also called Ray finned fish (no Muscle in fin) • Usually have a swim bladder, gas filled sac to regulate buoyancy • Chondrosteans- Sturgeons and paddlefish have a cartilage skeleton but ancestors were bony • Sturgeons have heavy bony plates covering the anterior body, caviar • Paddlefish have a large upper rostrum(paddle)

Sturgeon

Paddle Fish

Teleosts, Modern Bony Fish • Species exceed 24, 000 • 73% of the earths surface covered by water, ocean holds 99% of inhabitable area on earth • Aquatic environments have important selective forces • Water 800 times denser than air, difficult to move through but a fish spends less energy moving than a terrestrial organism

Nutrition • Earliest bony fishes were filter feeders and scavengers • The evolution of jaws (gill arches) and teeth (scales) changed fish into predators • Modern bony fish have peg teeth ( Hold prey) some modified into crushing teeth • Usually swallow prey whole • Some became filter feeders with modified gill rakers

Circulation and gas exchange • Two chambered heart with a closed system • Ocean contains 2. 5% of the oxygen present in air, so large quantities of water passed over gills • Bony fish have a muscular pump to move water over gills • Gas exchange occurs in the gill filaments, counter current exchange mechanism

Fish Gills

Filter feeders, Active predators

Counter Current System

Buoyancy Control • Many tissues have a greater density than water, bone is 2 x the density of water, fats and oils float • Fish use 4 methods to maintain buoyancy • Low density compounds in their tissues, liver in fish holds large amounts of oil • Fins provide lift by angling up as they swim • Caudal fin has larger upper lobe • Swim bladder provides buoyancy with air

Swim Bladder/ Lungs • Bony fish use a pneumatic Sac (swim Bladder) for buoyancy • Open swim bladders have a connection to the esophagus and can be filled by gulping air • Closed swim bladders (most common) are filled by the gas gland from the blood • Air is reabsorbed • from the swim bladder at the opposite end by the Ovale

Swim Bladder

Bulging Stomach due to Swim Bladder Expanding

Electric Fishes • Electric fish in Africa produce weak electric fields around their body to sense surrounding objects in murky water • Electric eel of South America uses organs in its trunk to produce over 500 volts • Electric Ray in pacific can produce 50 amps at 50 volts • These strong charges are used to stun or kill prey and discourage large predators

Electric Eel

Electric Ray