Lower vertebrates {fish} (Pisces) have one heart with one vena cava entering auricle, one auricle connecting to ventricle, and one aorta leaving ventricle. Fish have vascular gills. They have scales. Females lay eggs in water that males cover with sperm. Fish have ears. They are streamlined. They move by swishing tail right and left. They steer with fins. Fish include jawless fish (Agnatha), extinct jawed fish (Placodermi), cartilaginous fish (Chondrichthyes), and bony fish (Osteichthyes).
Fish have canals and openings {lateral line} running from head to tail on both sides, to perceive pressure changes and water-flow changes.
Some jawed bony fish had stump fins {lobefin}|, allowing crawling onto shore. Lobefins later became appendages.
Some bony fish make groups {school, fish}|, which concentrate breeding stock, minimize losses to predators, confuse predators, increase food or danger perception, and move together by sight and lateral line.
Fish have sacs {swim bladder}| that can fill with secreted gas for buoyancy.
Fish have gill slits covered by hard flaps {operculum}.
Fish have gill and neck bones {opercular bone, fish}.
Some bony fish had nasal passages {nares}| with internal openings into windpipe inside body, rather than externally to water. Nares allowed more-efficient breathing, moist and filtered air, and alternative air path through mouth, not just nose.
Some jawed bony fish had nasal passages inside to lungs {internal nares}, allowing more efficient breathing.
Agnatha {jawless fish} were first fish.
size
Jawless fish are mostly small but can be up to one meter long.
body
Jawless fish have cylindrical bodies, with no fins and no jaws. Distinct trunk is between head and tail. Head is independent of trunk. Pharynx separates digestion and respiratory pathways.
backbone
Cartilage backbone supports larger size and more speed.
digestion
Jawless fish prey on small organisms by scavenging and parasitism. They have a sucking disc around mouth. Some agnatha are vertebrate parasites. Jawless fish are not filter feeders.
circulation
Heart has one aorta leaving one ventricle and one vena cava entering one auricle.
circulation: blood
Jawless-fish have hemoglobin with one protein sequence.
skin
Outer-skin epidermis layer is protective and smooth. Inner-skin dermis layer contains blood vessels, skin glands, and neurons.
nervous system
Jawless fish have three brain parts: forebrain for smell, midbrain for sight, and hindbrain for hearing. Telencephalon has olfactory bulb. Optic tectum is for sight. Cortex has three cortical layers. Cerebellum associates with hindbrain for sensorimotor coordination. All vertebrates have similar brainstem serotonin-neuron patterns. Spinal cord distributes nerves to body and collects sense signals.
senses
Vestibular system has one or two semicircular canals and helps balance and vision. Frontal eyes, with no eye muscles and no lens, are for pattern detection and make retinoic acid. Jawless fish can detect prey and mates. Parietal eyes can detect sunlight level. Nostrils aided smell.
senses: pain
Jawless fish seem to feel pain.
behavior
Jawless fish can control sucking.
development
Neural crest is at neural-groove edges.
life cycle
Most jawless fish spawn in fresh-water streams, develop into larvae, metamorphose to adults, and swim back to ocean.
Eel-shaped cyclostomes {hagfish} can have round mouth, have eight tentacles, and eat dead fish by boring. Tongue has horny teeth.
Eel-shaped cyclostomes {lamper eel} {lamprey} (Petromyzontidae) has sucking mouths.
Extinct fish {jawed fish}| (Gnasthostomes) lived in ocean and had jaws.
evolution
Gnasthostomes were cartilaginous-fish and bony-fish ancestors.
bone
Tissue calcification makes tissue firmer. Bone allows strong muscle attachments. Bone allows more shapes, because parts can be soft, medium, or hard. Retinoic acid became homeotic-gene regulator, allowing vertebrates to have head bone formation to create cranium to encase and protect brain and allow more muscle-attachment sites for head movement. Neural crest allows new skull bones, jaws, teeth, peripheral nerves, and dentine plates, under homeotic-gene control.
bone: jaw
Head bones evolved to make muscled and bony jaws, which opened larger and allowed grasping, for greater food intake. Bony jaws were possible because vertebrates had evolved heads separate from bodies and had evolved homeotic genes and gene regulators.
blood
By gene duplication, hemoglobin had four protein sequences.
senses
Jawed fish had eye muscles and eye lenses and so better vision. Vestibular system had three semicircular canals.
nervous system
Jawed fish had thalamuses. Cerebellum was larger. Early jawed fish evolved oligodendroglia, which make myelin, which allows faster saltatory conduction and requires less energy to restore ion balance.
Chondrichthyes {cartilaginous fish}| include shark, skate, stingray, and electric ray. Sharks are fast, but others are slow. Cartilaginous fish live in ocean. They have cartilage skeletons. They have paired jaws. They have two fin pairs. They have scaly skin. They have five to seven gill pairs, which send water from mouth out gill slits. They have teeth that are large scales. They have motor maps in optic tecta. They represent sensations in midbrain.
Skates {skate} have wing-like pectoral fins and are flat diamond-shaped bottom feeders.
Rays {ray, fish} have wing-like pectoral fins and are flat and diamond-shaped.
Torpediniformes {electric ray} has electric organs on head sides and stays near bottom.
Tropical rays {manta ray} can be very large, pelagic, and plankton and small-fish eaters.
Rays {sawfish} can have sharp teeth on long flat snouts.
Dasyatidae {stingray} has long tail with one or more spines with poison. Spines are modified dorsal fin rays.
Sharks {shark} are carnivorous and have heterocercal caudal fins, tough skin, and small scales.
Large northern sharks {basking shark} can be plankton eaters and swim slowly at sea surface.
Tropical sharks {hammerhead shark} can be medium-size, be live bearing, and have flat bar-shaped heads with eyes at ends.
Jawed bony fish {teleost}| {bony fish} evolved.
bone
Fins have bony rays with muscles, allowing better control. Later, rays became fingers and toes.
skin
Bony fish have skin scales.
mouth
Bony fish have mouth at front end, allowing larger opening, more shape and size variation, more growth while maintaining streamlined shape, and larger brain, because fish can maintain streamlined shape even if brain grows.
lung
Some bony fish have lungs surrounded by blood vessels, allowing gas exchange from blood to air, to control buoyancy and extract more oxygen.
nervous system
Fish can detect features, intensities, textures, flows, and surfaces.
types
Fish include sea horse, lungfish, bass, trout, perch, flounder, swordfish, angelfish, tropical fish, goldfish, cod, barracuda, smelt, sardine, and anchovy.
dark gray, medium size, southern, long side fins, flat {angelfish} {angel fish}.
large mouth, filament for luring prey {angler fish} {goosefish}.
Toxotidae {archer fish} {archerfish} shoot water from mouth at insects and live in warm water.
Sphyraena {barracuda} have long cylindrical bodies and projecting lower jaws with long strong teeth.
Fish {crucian carp} can use lactic acid to make ethanol and so does not need oxygen.
Tropical fish with large fins {flying fish} (Exocoetidae) can glide after jumping from water.
large, sea-bass shape {grouper} (Epinephelus) (Mycteroperca).
Fish {grunion} can spawn on beaches at full moon in spring, at highest tide.
tropical, medium size {grunt}.
small fish {minnow}.
long, tubular, tropical {pipe fish}. family Syngnathidae.
Fish {porcupinefish} inflates by swallowing water or air when threatened, relates to puffer fish, and has spines.
East Coast, tropical {porgy} {sea bream} {scup} (Pagrus) (Sparidae).
Fish {blowfish} {swellfish} {globefish} {balloonfish} {puffer fish} (Tetraodontidae) (Tetraodontiformes) inflates by swallowing water or air when threatened and has no spines.
Fish {remora} (Echeneidae) sucking disk can attach to sharks.
Fish {seahorse} can be small, swim vertically, have bony plates, and have horse-head shaped heads.
large, broad shovel-shaped snout, freshwater, ancient {sturgeon}.
bottom feeding, no scales, broad head, wide mouth {toadfish}.
Deep ocean fish {viperfish} (Chauliodus macouni) eats crustaceans and small fish. First dorsal fin has photophores to attract prey.
North Atlantic, soft {weakfish} (Cynoscion regalis).
saltwater white fish {whitefish, fish}, except herring.
long thin upper jaw, related to sailfish and spearfish {marlin} (Makaira) (Tetrapturus).
large flat dorsal fin {sailfish}.
large, long bill at snout tip {swordfish, fish}.
Gulf of Mexico, long body, large silver scales, up to 2 meters and 100 kilograms {tarpon}.
Eels {eel, fish} live in fresh water and spawn in Sargasso Sea in North Atlantic Ocean.
large, colored, tropical reef {moray eel}.
long body, pointed tail {wolffish} {wolf eel}.
flatfish {flounder, fish}.
flatfish {halibut, fish}.
flatfish {plaice, fish}.
flatfish {pompano, fish}.
small flatfish, Pacific coast {sand dab}.
flatfish {sole, fish}.
large European flatfish {turbot}.
small, silver {anchovy, fish} (Engraulidae).
sprat {brisling}.
northern {herring, fish} (Clupeidae).
Small fish {pilchard, fish} can include sardines.
small, northern, silver, ocean and fresh water {smelt, fish}.
small European herring {sprat} (Clupea sprattus).
young or small pike {pickerel, fish}.
long, slender, duckbill {pike, fish}.
Teleosts {salmon, fish} (Salmonidae) can spawn in fresh water and live in sea, returning to home stream by smell.
northern coastal Atlantic, pink inside {Atlantic salmon}.
salmon {sockeye salmon}.
medium to large size, silver {trout, fish}.
very large {piracucu} {paiche} {arapaima} (Arapaima gigas).
North America, lake {bass, fish}.
east and central United States sunfish {bluegill}.
smooth skin, large flat head, long hairs {barbel} near mouth, ocean and freshwater {catfish}.
Europe, thick, spindle shape {chub}.
east Asia, red-orange color {goldfish} (Carassius auratus).
fresh water or ocean {mullet} (Mugilidae).
South America, tropical {piranha} (Serrasalmus).
Male fish {stickleback} can fight fish with red underbellies and court fish without red underbellies {key stimulus}. Stickleback fish build nests, using innate behavior.
small, South America and West Indies {guppy}.
live young, North and Central America {swordtail} (Poecilidae) (Cyprinodontiformes), related to southern platyfish {platy}.
small, striped, tropical, India {zebra fish} (Brachydanio rerio).
Fish {electric fish} (Gymnarchus) tail can generate weak electric voltages that cause discharges at 300/second. Electric organs along body detect electric field. Dorsal fin undulates to move fish forward without using tail. Objects in water alter electric field.
eel-like, South America {electric eel}.
Perciformes, Percomorphi, or Acanthopteri {perciform fish} {percoid} are largest vertebrate order, are 40% of all fish, look like perch, have ray fin, and began in late Cretaceous.
northern {cod} (Gadus morhua) (Gadidae).
Antarctica and south South America {white-blooded fish} {ice fish} (Channichthyidae).
Zanclus cornutus {moorish idol} (Zanclidae) is small tropical marine fish. Genus Heniochus butterfly fishes resemble Moorish Idols.
fresh water or ocean {perch, fish}.
small, America {sunfish} (Centrarchidae).
amber color, fork tail, warm water {amberjack} (Carangidae) {carangid} {hamachi}.
percoid {jack fish}.
carnivore, bluefin/horse mackerel, tropical {pilot fish} (Naucrates duclor).
tuna-like {skipjack} (Euthynnus).
tuna {albacore, fish}.
tuna {bigeye}.
large tuna {bluefin} {horse mackerel}.
streamlined {bonito, fish} (Sarda).
tuna {yellowfin}.
tropical {tunny} (Thunnus).
northern {mackerel, fish}.
Some jawed bony fish {salt-water lobe-finned fish} {lobefin fish} had lobefins, allowing crawling onto shore. Later, stumps became appendages.
lung
Nasal passages had internal nares openings into windpipe inside body, allowing more efficient breathing, moist and filtered air, and alternative air paths.
types
Rhipidistians are extinct. Later, Rhipidistians evolved to amphibians. Coelacanth fish (Crossopterygii) still survive today and are like Rhipidistians.
Paleozoic fish {coelacanth} are large, are bright blue to brown, have lobefins, and live in deep ocean.
Some lobefin fish {fresh-water lobefin fish} {fresh-water lobe-finned fish} had adults that lived in fresh water and on land.
fresh water
Because fresh water has no salt, they had to maintain hydrogen and salt ion balance in blood and tissues and had to control water drinking. Seawater ion balance is similar to that in cells. To live in fresh water, organisms need to pump out cell water to maintain salt and protein concentrations and to prevent bursting.
hind limb
Rear lobefins became specialized for pushing. Later, they became legs.
teeth
Teeth were for grasping but not cutting or grinding. Teeth grew, fell out, and grew back, repeating as animals grew.
hearing
Eardrum amplified sound for better hearing.
lung
They breathed using lungs. They had no gill bones and began gill loss. Later, gills closed.
evolution
Land vertebrates evolved from lobe-finned bony fish.
lobe-finned fish and tetrapods {sarcopterygian}.
Lobe-finned fish one meter long developed into four-legged fish {tetrapod}| (Tetrapoda) in shallow, plant-filled, fresh or brackish water, in tropics and subtropics. Perhaps, front limbs helped lift head above water to get more oxygen.
fins
Pectoral and pelvic fins gained feet and toes. Tetrapods have no tail fins.
bone
Vertebrae became interlocking. Neck became flexible after losing bones that joined head and shoulders. Snout became longer and head flatter. Gill and neck bones {opercular bone, tetrapod} disappeared. Longer ribs appeared. Pelvis became larger.
evolution
Most early lobefin fish were not tetrapod ancestors: Kenichthys [-400000000], Osteolepidids [-394000000], Eusthenopteron [-388000000], Panderichthys [-385000000], Elpistostege [-384000000], and Livoniana [-384000000]. Most early tetrapods are extinct and were not living-tetrapod ancestors: Elginerpeton [-378000000], Ventastega [-370000000], Acanthostega [-368000000], Ichthyostega [-366000000], and Tulerpeton [-364000000].
Sarcopterygians {lung fish} {lungfish} can have one or two lungs, live in freshwater, and have lobefins.
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Date Modified: 2022.0225