Fishes

Chapter 24

I. Diversity

26,000 living species—more species than all other vertebrate groups combined

Adapted to live in a medium 800 x more dense than air

Can adjust to salt and water balance of environment

Gills extract oxygen from water that has 1/20th the oxygen of air

Aquatic environment both shaped and constrained their evolution

II. Ancestry and Evolution A. Ancestor

Descended from free-swimming protochordate ancestor

B. Agnathans Earliest fish-like

vertebrates Include extinct

ostracoderms, and living lampreys and hagfishes

C. Placoderms Fish with paired

appendages and jaws that went extinct in Carboniferous with no living descendants

D. & E. D. Cartilaginous Fishes

Lost heavy armor and adopted cartilage as skeleton

Flourished during some periods, becoming nearly extinct during others

E. Acanthodians Resemble bony fish but

have heavy spines on all but caudal fin; sister group to bony fishes

Went extinct in lower Permian

F. Bony Fishes

Dominant fishes today 2 distinct lineages—ray finned and lobe

finned Ray-finned radiated to form modern bony

fishes Lobe-finned include lungfishes, the

coelacanth, and are sister group to tetrapods (amphibian ancestors)

III. Superclass Agnatha: Jawless Fishes

A. CharacteristicsLack jaws, internal ossification, scales,

or paired limbsPore-like gill openings and eel-like body

B. Class Myxini: Hagfishes 43 species Entirely marine Scavengers and predators

of annelids, molluscs, dead or dying fishes, etc

Nearly blind but locates food by acute sense of smell

Rasps hole into prey then eats from inside out with plate-like tongue

Glands secrete substance that becomes slimy in contact with seawater

C. Class Cephalaspidomorphi 1. Diversity

41 species; 22 in North America and of these, half are non-parasitic brook variety

Marine lampreys can grow to length of 1 m.

All lampreys reproduce in freshwater streams, dying soon after

2. Parasitic Lampreys Attach to fish by

sucker-like mouth and sharp teeth rasp away flesh

Anticoagulant injected into wound to stimulate flow of blood

Wound may be fatal to host fish

Non-parasitic lampreys do not feed; digestive system degenerates and fish die after reproducing, within 2-3 years

3. Sea Lamprey Invasion No lampreys existed in

Great Lakes prior to 1829 when shipping canals were built

By the 1940’s, they existed in all the lakes

They decimated almost all fish species until populations finally declined due to lack of food and control measures

IV. Class Chondrichthyes A. Overview

850 species nearly all marine; 28 species live in freshwater Ancient lineage but have survived due to well-developed

sense organs and powerful jaws making them successful predators

Largest living vertebrates, after whales, reaching up to 12 m in length

Whale shark reaches 43’ in length

B. Subclass Elasmobranchii 1. Sharks

A. OrdersCarcharhiniformes—tiger and bull sharks which are coastal sharks and the hammerhead

Lamniformes-- white and mako sharks which are large pelagic sharks

Squaliformes—some of these are deep sea dwellers like dogfish sharks

Orectolobiformes—carpet sharks like bamboo, nurse, and whale sharks

Sharks

More Sharks

b. Outer Physiology Streamlined fusiform body

shape Pointed nose with paired

nostrils in front of ventral mouth; on hammerhead, nostrils on ends of “hammer”

Lateral eyes without lids Tail has longer upper lobe

(heterocercal) Paired pectoral and pelvic

fins, 1-2 dorsal fins, 1 caudal fin, and sometimes an anal fin

Tough, leathery skin with placoid scales that reduce water turbulence

Body Structures of a Shark

c. Senses Olfactory organs can

detect chemicals diluted 1/10 billionth their original concentration

Lateral line senses low frequency vibrations of prey over large distances

Excellent vision, even in dim water, used at close range

At close range, sharks are guided to prey by electric fields surrounding all animals

d. Inner Physiology Sharp triangular teeth in

upper and lower jaws; arranged in rows that are constantly replaced

Mouth leads to pharynx with openings to gill slits

Osmoregulation accomplished by rectal gland which secretes sodium chloride; nitrogenous compounds are also retained in blood to increase solute concentrations, making more on par with seawater

e. Shark Attacks Only 32 species ( of 350) have been

documented to attack humans with another 36 considered potentially dangerous; these typically are the larger size sharks; 80 % of sharks are harmless

Great white, tiger, and bull sharks are the more aggressive species

50-75 attacks occur each year, with 8-12 fatalities; in contrast 30-100 million sharks are killed every year

Attacks usually occur by sandbars, steep drop offs, or by river inlets and are associated with mistaken identity,territorial behavior, or feeding behavior

2. Rays

A. OrderRajiformes—skates, sawfish rays,

electric rays, stingrays, manta rays and others

Make up half of all species of Elasmobranchii

b. Form and Function

Specialized for benthic life Flattened dorsoventrally; enlarged pectoral

fins are used as swimming wings Water used in respiration enters large

spiracles in head Teeth adapted to act as rollers to crush

invertebrates and sometimes small fish Stingrays have whip-like tail with spines

and venom glands Electric rays have electric organs on sides

of head

C. Subclass Holocephali: Chimeras

31 species Ratfishes Diverged from earliest shark lineage Mouth has flat plates for crushing

invertebrates; also feeds on seaweed and small fish

D. Reproduction and Development

Internal fertilization Oviparous sharks and rays lay an egg capsule

immediately after fertilization that attaches to kelp with tendrils; may take up to 2 years before mini adult hatches

Ovoviviparous sharks retain fertilized eggs in reproductive system where they are nourished by yolk of egg; “live” birth

Viviparous sharks nourish embryos with maternal bloodstream; “live” birth

Live births make it more likely more of the young survive but no other care is given after birth

Embryo Development

V. Superclass Osteichthyes A. Origin, Evolution, and Diversity

Lineage developed in Silurian and now accounts for 96% of all fishes and all tetrapods

Bone replaces cartilage as fish developsLung or swim bladder evolved from an

extension of the gut; gas filled, it aids in buoyancy

Bony operculum, a flap covering the gills that rotates outward, draws water more efficiently over them

Specialization of jaw musculature improves feeding; also unique dental characters

B. Class Actinopterygii 23,600 species comprise the ray-finned fishes Most familiar fish type

a. Palaeoniscids

Earliest forms, existing from late Silurian to late Paleozoic

Small, large eyes, dorsal fin with bony rays, heterocercal tail, and interlocking scales

Survived as other fishes declined, suggesting some adaptive advantage

Gave rise to the chondrosteons and the neopterygians

b. Chondrosteons

Most primitive characteristics Heterocercal tail and ganoid scales Living species include sturgeons,

paddlefishes, and bichirs

c. Neopterygians One lineage gave rise

to modern bony fishes, the teleosts

Living species are bowfin and gars which gulp air and use vascularized swim bladder to supplement the gills

d. Teleosts

96 % of all living fishes; half of all vertebrates

10 mm to 17 m; up to 900 kg in weight Found at 5,200 m to 8,000 m below sea

level Some can live in hot springs at 44 oC while

others can survive in Antarctic –2 oC. Some live in salt concentrations three

times seawater; others in swamps devoid of oxygen

2. Morphological Trends Heavy armor replaced by light

cycloid or ctenoid scales which made fish more mobile; some fish such as eels and catfish have completely lost scales

Fins changed to provide greater mobility and serve a variety of functions: braking, streamlining, and social communication

Homocercal tail allowed greater speed and buoyancy

Swim bladder switched from primarily respiratory to buoyancy in function

Jaw changed to increase suctioning and protrusion to secure food

Cycloid

Ctenoid

C. Class Sarcopterygii 1. Diversity

Only 7 species alive today; 6 lungfishes and 1 coelacanth

Early ones had lungs as well as gills, heterocercal tail; later tail became symmetrical

Skin covered in heavy scales overlaid by an enamel

Fleshy, paired lobes are used to scuttle along bottom

South American and African lungfishes can survive out of water or long periods of time

2. Coelacanth Thought to have been

extinct for 70 million years until one was dredged up off of coast of Africa in 1938

More were caught off the coast of the Comoro Islands in 1998

VI. Structural and Function Adaptations

A. Locomotion 1. Mechanism

Trunk and tail muscles propel fish forward by undulations

Large, rigid head minimizes yawVery rigid body creates less yaw and a fast fishThe largest fin is the tail or caudal fin for rapid

forward movement.Dorsal fins on the top and anal fins underneath

assist with lateral stability.Pectoral fins behind the gill covers

(operculum) assist with hovering and slow turning.

Pelvic fins are often small for open water swimmers but larger on bottom dwellers which use them for resting on.

2. Speed and Energy

Larger fish swim faster Short bursts of speed are possible for a

few seconds Swimming is most economical means of

motion since water buoys the animal; swimming expends 0.30 Kcal, 1.45 Kcal for walking, and 5.43 Kcal for flying

B. Swim Bladder

Fish are slightly heavier than water A shark has a very fatty liver that makes it

a little buoyant; must also keep swimming to move it forward and angle itself up

Bottom dwelling fishes also lack swim bladder

Fish can control depth by adjusting volume of gas in swim bladder

Gas gland removes or adds gases from blood to remove or add gas to bladder

Some fish gulp air to fill swim bladder

C. Respiration Gill filaments are folds of tissue inside the

pharyngeal cavity covered by the operculum Continuous water flow opposite blood flow

through capillaries maximizes gas exchange allowing some fish to remove 85% of O2 from H2O

Some fishes are dependent on ram ventilation as well, in which forward movement pushes more water over gills; such fish will die in an aquarium

Lungfish use lungs; eels use skin; bowfin uses gills at low temperatures and air bladder at higher temperatures; electric eel has degenerate gills and must gulp air

D. Osmotic Regulation

1. Freshwater FishesFreshwater has less salt than blood of

fish so water tends to enter fish’s cells and its salts tend to leave

Hyperosmotic regulators: kidney pumps out excess water and salt absorbing cells in skin remove salts from water and add to blood

Euryhaline fishes live in estuary environments where they are in contact with both fresh and salt water

2. Marine Fishes

Blood has lower salt content than surrounding water so tend to lose water and gain salt

Hypo-osmotic regulators: fish drinks water bringing in more water but also salt; salt is carried by blood to gills where it is secreted by salt-secretory cells, some salt leaves in feces, and others are excreted by kidneys

E. Feeding Behavior Most time devoted to searching for food and

eating Most carnivores-feed on zooplankton, insect

larvae, and other aquatic animals Most don’t chew food since it would block flow of

water across gills; swallow food whole although a few have teeth that crack prey or have some molars in throat

Some herbivores--eat plants and algae Suspension feeders eat plankton, using gill rakers

to strain food; these fish swim in large schools Also have omnivores, scavengers, and parasites Stomach used for storage; intestines absorb and

digest nutrients

F. Migration

1. EelsCatadromous—develop in freshwater but spawn

in seawaterAdult eels spawn in Sargasso Sea at depths of

300 m.Larvae drift for 2 years before developing into

elvers; males remain in brackish water; females swim hundreds of miles up rivers

Females mature for 8-15 years before returning to the sea ( 8 months to complete journey)

American eels are separate species from European eels

2. Salmon Anadromous—living in sea but spawing in

freshwater 6 Pacific salmon species, and 1 Atlantic salmon

species that migrate Pacific species migrate downstream, live in

Pacific for 4 years, and then return up the same stream it was spawned in

Young fish are imprinted with the odor of their stream

Pacific salmon spawn and then die Endangered by stream degradation, logging,

pollution, and hydroelectric dams

G. Reproduction Most dioecious with external fertilization and

development Some are ovoviviparous where eggs develop in

ovarian cavity—sharks, guppies, mollies Oviparous marine fish lay large numbers of eggs,

upwards of several million Nearshore or bottom dwelling fish lay fewer,

larger nonbuoyant sticky eggs Some fish bury eggs, attach them to vegetation,

incubate them in their mouths Freshwater fish produce fewer, nonbuoyant eggs,

and more care is usually provided Many freshwater fish also have elaborate mating

dances before spawning

H. Growth Egg starts to take up water after it is laid, outer

layer hardens, and cell division begins Yolk is consumed during development Fish fry hatch carrying semitransparent yolk sac

to supply food until it can forage As fry change to adult, it may undergo dramatic

changes in body shape, fins, color patterns, etc Growth is temperature dependent; warmer fish

grow more rapidly Annual rings on scales reflect seasonal growth

cycles Most fish continue to grow throughout life and do

not stop at maturity

Fish Development