Lecture 1
Fish Diversity
Nearly 25,000 Named Species
Possibly 30,000 More
+ 200 per year being described
Total Vertebrates = 45,000 species
Fish Habitats
WATER!!
-1.8 to 40° C
pH 4 to 10+
Salinity 0 to 90 ppt
Depth 0 to 7,000 m
Fish Evolution
Fish for at least 500 million years
New found fossils date to 560 million years old
Modern fishes here at least 400 million years
History of Ichthyology
Aristotole
384-322 B.C.
Distinguished fish from whales
Recognized 117 species of fish
Observed some fish natural history
History of Ichthyology
Middle ages
Pierre Belon (1517-1564)
Natural History of Fishes
Recognized 110 species from anatomy
H. Salviani (1514-1572)
Studied Italian fishes
Guillaume Rondelet (1507-1566)
De Piscibus Marinum - fish knowledge, 244 species
History of Ichthyology
Carolus Linnaeus (1707-1787)
God creates it, Linnaeus names it
Binomial classification
Mentor and friend of Peter Artedi
History of Ichthyology
Here lies poor
Artedi, in foreign land pyx'd
Not a man nor
a fish, but something betwixt,
Not a man, for
his life among fishes he past,
Not a fish,
for he perished by water at last.
George Shaw (1751-1813)
Peter Artedi (1705-1735)
The Father of Ichthyology
Recognized 5 fish orders
Divided orders into genera
Drowned before studies were published
History of Ichthyology
Marc Elieser Bloch (1723-1799)
Systemae Ichthyologiae
Standard reference for 50+ years
Series of volumes of plates
Did not start publishing until 56 years old
History of Ichthyology
Georges Cuvier (1769-1832)
Father of Paleontology & Anatomical Studies
Histoire Naturelle des Poisssons
22 volumes
Included 4541 species
Classification
Anatomical studies
Fish interrelationships
Helped by student, Achille Valenciennes
History of Ichthyology
Louis Agassiz (1807-1873)
Published treatise on fish of Brazil at age 21
Series of volumes on fossil fish
Groundwork for evolutionary work on fish
Agassiz did not accept the concept of evolution
History of Ichthyology
Johannes Müller (1801-1858)
Developed currently used classification system
Revised Agassizs system
History of Ichthyology
Notable American Ichthyologists
Edward Drinker Cope (1840-1897)
Freshwater & Fossil fishes
Copeia
David Starr Jordan (1851-1931)
Fishes of North and Central America
Carl L. Hubbs (1894-1979)
Taxonomist
Lecture 2
Fish Form and Movement
External Form
Provides a quick appraisal of its way of life
Most fish can be put into one of several body categories
There are exceptions for specialized lifestyles
Fusiform
(streamlined)
Often called rover-predators
Constantly on the move
Always searching for prey
Pointed head
Terminal mouth
Narrow caudal peduncle
Forked tail
Fins evenly distributed
Characteristic of stream fish
Compressiform
(laterally compressed)
Capable of quick bursts of speed
Not in constant motion
Predatory fish
Depressiform
(flattened dorsoventrally)
Bottom-dwelling fish
A few are adapted to swim in open water
Large pectoral fins for movement
Anguilliform
(eel-shaped)
Blunt or wedge-shaped heads
Tapering or rounded tails
Fins are small to absent
Adapted to moving through crevices
Many are predators of small invertebrates
Filiform
(thread-shaped)
Extreme version of eel-shape
Largest part of body is the head
Taeniform
(ribbon-shaped)
Eel-like, but compressed
Sagittiform
(arrow-shaped)
Often lie-in-wait predators
Most are piscivores
Use quick burst of speed to emerge from hiding place
Dorsal fin near caudal peduncle
Globiform
(round)
Body has length about equal to width
Rattail
Caudal area is narrowed to posterior point
Usually found in deep-sea
Mostly scavengers
Odd-Shaped
A few fish do not easily fit into a category
Usually highly specialized fish
Mouth Position
Often tells the where and what of feeding
Four distinct mouth positions
Superior
Terminal
Subterminal
Inferior
Superior Oriented Mouth
Mouth opening points upwards
Surface oriented fish
Usually feed on objects on the waters surface
Commonly found in oxygen poor water
The surface layer tends to have the highest concentration of O2
Terminal Mouth
Mouth is at the extreme anterior
Feeding on what is directly in front
Often predators
Subterminal Mouth
Mouth is mostly ventral
Bottom feeders
Many also have barbels (whiskers)
Many are scavengers or herbivores
Inferior Mouth
Mouth is used to suck things off the bottom
Most are scavengers
Scales
Type, size, and number tell a lot about a fishs way of life
Evolved independently in cartilaginous and bony fish
Scales offer a trade-off between protection and movement
All fish scales are one of four types
Some fish lack scales
Placoid Scales
Found in cartilaginous fish
Tooth-like structures
Include basal plate containing some bone
Have pulp cavity and dentin
Outer layer is vitrodentin (similar to enamel)
The spine of a sting ray is a modified placoid scale
Ganoid Scales
Has a typical rhomboid shape
Anterior peg-like extension overlapped by preceding scale
One outer layer is bone
Non-flexible
Ganoine (enamel-like)
Cycloid Scales
Round, flat, and thin
Flexible bony layer
Covered with epidermis
Includes mucus glands
Curculi (growth ridges) are present
Enamel layer present
Ctenoid Scale
Structure like cycloid
Sometimes these two types are called elasmoid scales
Have comb-shaped projections on posterior, called ctenii
Improve swimming efficiency
Have minute exposed spines
Makes the fish feel rough
Cosmoid Scales
Found only in extinct lobe-finned fish
Contained layer of non-cellular cosmine
Below cosmine was vascularized bone
Living coelacanth may have simplified cosmoid scales
No cosmine
Fins
Structure supports an independent evolutionary history of cartilaginous
and bony fishes
Most fish have two sets of paired fins and four unpaired fins
Fins are used to propel, stabilize and maneuver
Internal Support for Fins
Supports have independent evolutionary history in bony & cartilaginous
fish
Fin rays are internal supports for fins
Ceratotrichia (cartilaginous)
Stiff, unbranched, unsegmented
Lepidotrichia (bony fish)
Flexible, branched, segmented
True spines may occur that emerge into fins
Paired fins
Pelvic fins
Most variable in position
Ancestral, = ventral, toward posterior
Derived = thoracic
Rarely in front of pectoral
Pectoral fins
Usually on sides
Pelvic Fin Placement
Pelvic Fin Modifications
Pectoral Fin Modifications
Dorsal & Anal Fins
High degree of differences in size
Dorsal varies in position considerably
Some fish have more than one dorsal fin
Dorsal may have
spinous and soft-rayed portions
Dorsal Fin Modifications
Caudal Fin
Shape related to normal swimming speed
Two general types
Homoceral
Upper & lower lobes about equal
Vertebral column ends at peduncle
Found in most bony fish
Heteroceral
Upper lobe significantly longer than lower
Vertebral column extends into upper caudal fin
Isoceral (considered heteroceral evolutionarily)
Lacking lobes
Adipose Fin
Fleshy dorsal appendage
Lacking in many fish
Between dorsal & caudal fins
Lacks rays
Function not well understood
Spines
May be present or absent in fins
Usually on dorsal, anal, & pectoral fins
Common in many bony fishes
Evolved many times independently
Some also associated with poison glands
Differing Muscle Fibers
Different proportions of muscle fibers occur
Three types of muscle fibers
Red (slow)
High myoglobin aerobic only
Constantly moving fish
White
Thick fibers without myoglobin
Used for quick movement
Pink
Intermediate
Fish Movement
Move by a variety of means
Passive drift
Burrow
Walk
Crawl
Glide
Fly
SWIM !! forward and backward
How Do Fish Swim?
Undulations of body
Movement of fins
The water around the fish is relatively incompressible
Fish push off from surrounding water
Body bends from side to side and does not shorten
Lateral Flexures of Body
Propel fish forward
Body makes a propulsive wave posteriorly
More waves = faster swimming
Shape of body decreases drag (resistance to movement)
Swimming Modes of Fish
Because of different fish body shapes there are different forms of
body movements for swimming
Four distinct modes are found
Anguilliform
Subcarangiform
Ostraciform
Carangiform
Anguilliform Swimming
Found in flexible long-bodied fish like eels
Whole body is flexed into lateral waves
Also used by some shorter bodied fish when swimming slow
Carangiform Swimming
Involves throwing the body into a shallow wave
These fish usually have a long forked caudal fin
Includes thunniform
Fish with low drag
Fastest of all fish
Subcarangiform Swimming
Like Carangiform, with exceptions
Undulate body less than one full wavelength
Speeds greater than one body length per second
Ostraciform Swimming
Only body flexing is at the caudal peduncle
Can not generate speed
Swimming with fins
Some fish can swim at high speed using only fin muscle movement
Allows for coordinated movements
Lecture 3
Circulatory System of Fish
Special conditions for fish circulation
Environment is oxygen poor
Heart is simplest of vertebrates
Fish have less blood volume than other vertebrates
Adaptations by fish
Composition of blood
Morphology of circulatory apparatus
Behavioral responses to oxygen availability
Functions of the Circulatory System
Delivers oxygen
Delivers nutrients
Removes metabolic waste
Fights pathogens
Components of the Circulatory System to Study
Blood
Erythrocytes
Leukocytes
Structure of Hemoglobin
Vascular system
Heart
Vessels
Formation of Fish Blood Cells
Formed from hemocytoblast
Blood forming site differs
Agnatha
Mesodermal envelope around gut in hagfish
Fatty tissue dorsal to nerve cord in lampreys
Elasmobranchs
Leydig organ (near esophagus)
Epigonal organ (around gonads)
Spleen
Formation of Fish Blood Cells continued
Teleosts
Kidney
Spleen
Cranium
Thymus
Fish bone has no marrow
Erythrocytes
Most abundant fish blood cells
Nucleated
Size range exists (elasmobranchs usually larger, but fewer)
More active species have more red blood cells
Hemoglobin of Fish Erythrocytes
Primary means for transporting oxygen
In some fish up to 15% may be in plasma
A few fish have no hemoglobin (rare situation)
Environmental oxygen high
Low metabolic requirements
Special cardiovascular adaptations
Fish Hemoglobin Characteristics
Structure is different in different fish
Monomeric
Single-heme peptide molecules
Much like myoglobin
Found in Agnatha
Tetrameric
Four peptide chanis
May differ in many features
Composition of amino acids
Affinity for oxygen
Elecrophoretic ability
Some salmonids have up to 18 different hemeglobins
Having Different Hemoglobin Types
Different Hemoglobins have different responses to temperature and
oxygen absorption
Allows fish to deal with changing conditions
Important for migratory species
Some fish gain or lose types as they age
Blood Oxygen Affinity
pH
Decreasing pH decreases affinity
Often associated with carbon dioxide
Carbon dioxide
Increase in CO2 drives off O2 (Bohr effect)
Decrease in blood pH magnifies Bohr effect
Temperature
Increase in temperature depresses oxygen affinity and capacity
Results in fish having narrow temperature tolerances
Organic phosphate
ATP depresses O2 affinity
Urea increases O2 affinity
Leukocytes
Less abundant than erythrocytes
Provide a mechanism for blood clotting
Rid the body of foreign materials
Several different types
Lymphocytes
Can vary in size
Cell dominated by nucleus
Important for immune system via antibody production
There may be some phagocytic activity
Monocytes
Cell outline may be quite irregular
Phagocytes of foreign particles
Attracted to foreign substances
Use pseudopods to engulf antigens
Granulocytes
Leukocytes with cytoplasmic granules
Neutrophil
Migrate to sites of bacterial infection
Phagocytic or bacteriocidal
Basophil
Not found in all fish
Phagocytic
Eosinophil
phagocytic
Non-Specific Cytotoxic Cells
Equivalent to natural killer cells
Lyse tumor cells
Lyse protozoan parasites
Thrombocytes
Function in blood clotting
Cytoplasm spreads into long threads
Cell shape varies, but often has spikes
Fish Circulatory System
Primary circulation
Closed system
Heart
Arteries
Capillaries
Veins
Secondary circulation
Collects blood that is outside the primary
Originally thought to be lymphatic
No lymph or lymph nodes
Divisions of Primary Circulation
Branchial circulation
Blood from heart through gills
Systemic circulation
Blood from gills to body to heart
Blood flow is continuous from heart, to lungs, to body, back to heart
Proximity of Heart & Gills
Exceptions to Normal Circulation
Hagfish have accessory inline hearts
Lungfish have pulmonary circulation
There are also many small adaptations in some species
Structure of the Fish Heart
Four chambered heart
All four chambers are in line
The heart pumps only venous blood
Except for a few air breathing fish, all blood is pumped to the gills
Chambers of the Fish Heart
(1) Sinus venous
Collects blood from venous ducts
(2) Atrium
Accelerates blood flow
(3) Ventricle
Large muscled chamber
Provides propulsive flow for circulation
(4) Bulbus arteriosus (bony)
Conus arteriosus
Changes blood from a pulse to continuous flow
Conus Arteriosus vs. Bulbus Arteriosus
Conus Arteriosus
Contractile
Cardiac muscle
More than one valve
Bulbus Arteriosus
Elastic
Mostly connective tissue
One valve dividing it from ventricle
Regulation of the Fish Heart
Self-regulating
Timing can be modified by brain
Pace is set by pacemaker cells
Many areas show pacemaker activity
The Hagfish Heart
Most primitive
Sinus venous well developed
Divided into two parts to receive different veins
Bulbus arteriosus
Have 3 additional hearts
Caudal heart in head
Brachial heart near gills
Portal heart pumps blood through liver
Lamprey Heart
Largest of fish hearts
Atrium overlies ventricle
Bulbus arteriosus
Right common cardinal vein empties into atrium
Elasmobranch Heart
Conus arteriosus
Sinus venosus with almost no cardiac muscle
Ventricle has two muscle layers
Compacta = compact outer layer
Spongiosa = inner layer
Teleost Heart
Variation exists across the group
Sinus venous is thin walled
Most have bulbus arteriosus
Some have conus arteriosus (usually more primitive)
Lungfish Heart
Atrium is divided into two parts by an incomplete septum
Functional 3 chamber heart
Like amphibians
Right atrium larger than left
Right = deoxygenated from sinus venosus
Left = oxygenated from pulmonary vein
Lecture 4
Buoyancy & Thermal Regulation
Why do we study these two functions together
Swimbladders of some fish and heat-exchange organs of others are
morphologically very similar
Both deal with exchange across blood vessels
Buoyancy
Fishes have two means of maintaining buoyancy
Neutral buoyance
Regulation by swimbladder
Neutral Buoyancy
Many fish are functionally weightless in water
This allows them to save energy while staying in a certain area
What is Required for Neutral Buoyancy?
Specific gravity must equal that of surroundings
Fresh water sp. gr. = 1
Salt water sp. gr. = 1.026
Different regions may have slight specific gravity differences due
to dissolved materials
Strategies to Maintain Neutral Buoyancy
Body made of large quantities of low density compounds
Fins are shaped and angled to generate forward lift
Reduction of heavy tissues like bone
Having a swimbladder filled with an appropriate amount of air
Low Density Bodies
Many fish have large quantities of lipids
Specific gravity < 1
Large livers filled with squalene
Hydrocarbon sp.gr. 0.8
A few fish have trigliceride oils in bones
Fins Designed for Lift
Leading edges of fins help maintain position
Small amount of energy gives large amount of lift
Also, body drag is eliminated by shape of fins and body
Reduction of Heavy Tissue
Bones are thin
Living in water does not require as much support
Sp. gr. of bone = 2.0
Cartilage is less dense than bone
Sp. gr. = 1.1
Many fish do not have a bony skeleton
Oddities for Maintaining Neutral Buoyance
Deepsea Acanthonus armatus has enlarged cranial cavity filled with
light water
Oilfish, Ruvettus sp. have around 15% of body weight in was esthers
Swimbladder
Major organ for buoyancy control
Allow for precise control of total body specific gravity
Normally 5% of marine fish body, 7% of freshwater body
Types of Swimbladders
Physostomous
Have a connection between the swimbladder and gut (Pneumatic Duct)
Mostly ancestral, soft-rayed teleosts
Physoclistous
No connection between swimbladder and gut
Swimbladder is a closed structure
Physostomous Swimbladders
Fish must swallow air to deliver it to the swimbladder
Requires these fish to live in shallow water
They cannot take in enough air to be buoyant at deep water and actually
move to deep water
Control of Physostomous Swimbladder
Air is controlled by a pneumatic sphincter muscle
Deflation is a gas-spitting reflex (gas-puckerflex)
Physoclistous Swimbladder
Swimbladder is inflated via circulatory system
Rete mirabile (wonderful net)
Gas gland
Fish are able to live away from the surface
Rete Mirabile
Blood flows through rete capillaries
Materials enter the gas gland from the capillaries
Gas gland tissues produce acid
Glycolitic transformation of glucose (produces HCO3-)
HCO3- dehydrates to CO2
Filling the Swimbladder
CO2 diffuses from gas gland into swimbladder
Partial pressure from depth of fish regulates the amount of gas that
diffuses
Modified Swimbladders
Many size modifications occur
Some fish have more than one swim bladder
Often fish with great vertical movements
Allows them to gain or lose air more quickly
Bottom Dwellers
Swimbladder is not needed
Reduced
Vestigial
Absent
Neutral buoyancy is not an advantage
Negative buoyancy is desired
Species Living in Flowing Water
Usually have reduced swim bladders
Less buoyancy helps them to maintain a given area
Their buoyancy requirement is met by other means than the swimbladder
Mola mola
Has no swimbladder
Commonly a surface dweller sometimes floats on the surface
Large amounts of body fluid that are about ½ the specific
gravity of seawater
Fish Body Temperature
Most fish are about 0.3 degrees above water temperature
Due to heat produced by muscle
Some fish conserve body temperature by thermoregulation
Thermoregulation
Most fish are not warm bodied
A few continuous swimming species have mechanisms for heat
exchange
Benefits of Maintaining Warm Bodies
Allows muscles to work more efficiency in cold surroundings
Makes it easier to catch-up to food
Modifications for Thermoregulation
Heat exchange retia mirabilia
Conserve heat produced by metabolism
Large cutaneous veins and arteries
Transport of blood without absorbing core heat
The Brain Heater
A few fish have a mechanism to locally warm the brain & eyes
This has evolved twice
Provides foraging success in deep, cold waters
Rapid & high cycling of skeletal muscle in this area
High mitochondria, enzyme activity
Lack of organized contractile elements
Lecture 5
Hydormineral Balance in Fish
The Osmotic Problem
Without adjustments
Marine fish dehydrate
Freshwater fish over hydrate
Must have organs that maintain balance
Kidneys
Gills
Special organs
Strategies for Osmoregulation
Osmoconforming
No regulation
Found in hagfish
Can live in only a narrow range of salinities (stenohaline)
Elasmobranch strategy
Internal salt concentration = 1/3 that of saltwater
Concentrate inorganic salts in blood
Blood salt concentration becomes saltier than seawater
Most is bound in urea
Marine teleost strategy
Continually replace lost water by drinking
Water is osmotically leaving body via skin
Excess salt elimination
Chloride cells in gill filaments & opercular skin
Chloride Cells
Remove salts
Salts are swept away by water moving past gills
Strategies for Osmoregulation
Freshwater fish strategy
Operate hyperosmotically
Constantly gain water
Excess water excreted by kidneys
Produces very dilute urine
The Fish Kidney
Paired organ, except in Coelacanth
Posterior portion has excretory function
Anterior portion is subject to modification
Reproductive function
Hemopoietic
Lymphoid
Producing dillute urine
Water absorbed into blood
Blood is filtered by kidney
Kidney eliminates water, conserves many ions
Factors Affecting Urine Formation
Blood pressure
Glomerular filtration
Tubular reabsorption
Hormone mediation
Renin
Angiotensin
Atrial natriuretic peptide
Arginine vasotocin
Prolactin
Ionic Regulation in Fish
Some ion regulation requires the expenditure of energy
All fish must regulate some ionic compounds
There are five different strategies used by different groups of fish
Strategies for Ionic Regulation
Hagfish strategy
Some Na+ is secreted in slime and possibly other ions
Some ions are secreted in urine
Elasmobranch strategy
Ingest significant amounts of Na+ & Cl-
Excretion by rectal gland
Also use kidneys and chloride cells
Marine teleost & lamprey
Use selective excretion
Kidney minimizes water loss
Not much urine produced
Kidney does not eliminate ions efficiently
Chloride cells do most ion excretion
Alpha chloride cells
Euryhaline & Diadromous teleosts
Euryhaline = estuarine & intertidal fish
Fluctuations in salinity
Diadromous = spend part of life in fresh/part salt
Change physiology
Change behavior
Drink or stop drinking
Freshwater teleosts
Use epithelial chloride cells
Beta chloride cells
Excretion of ions is usually minimal
Na+ is often exchanged for ammonia (NH4+)
Rids body of metabolic waste ions
Stressors & How Fish Deal
Stressors stimulate physiological exchange
Examples of stressors
Excessive exercise
Hypoxia
Netting & Handling
Types of physiological changes
Adaptive = allow fish to respond to emergency
Detrimental = lead to adverse effects
Example of Stress Responses
Mobilization of glucose
Lamellar recruitment
Increased gas exchange
Many sympathetic metabolic changes
Many endocrine responses
Mostly coticotropin releasing factors
Freezing Resistance in Fish
Most fish are not subject to freezing if their environment does not
freeze
Body fluids are hyperosmotic or isoismotic
Marine teleosts are a different story
Environment has a higher salt concentration than body
Their environment could stay unfrozen, but their body could freeze
Dealing with Below Freezing Temperatures
A few teleosts increase osmolality
Example: rainbow smelt
Increases gycerol and urea concentrations
Depresses body freezing point
Some fish develop antifreeze
Glycopeptides or Peptides
Interferes with ice crystal growth
There are still limits
Best case is not quite to 2 degrees C
Adaptations to Living in Extreme Cold
Antifreeze
Aglomeular kidney
Conserves instead of filters glycopeptides
Syntheis of antifreeze peptides in liver
Also some in skin, scales, & gills
Acid-Base Balance
Homeostasis requires a very narrow range
Changes in temperature or CO2 content can alter blood pH
Ways to Maintain Proper pH
A large amount of CO2 can bind to Hemoglobin
Many heme groups are not filled with O2
Most CO2 in red blood cells is then easily converted to HCO3-
CO2 easily leaves blood plasma & diffuses at gills
Ways to Maintain Proper pH
Hyperventilating washes blood of CO2
Used when there is an excess accumulation
Bicarbonate also acts as a buffer in blood
Maintenance of the correct pH restricts most fish to a narrow, preferred
water pH
Lecture 6
Nutrients for Energy & Growth
Feeding
Two ways of classifying feeding by fish
Feeding Habits
Diet
These two classifications can be incorporated to give a very
descriptive class
Feeding Based on Habits
Detritivore
Herbivore
Carnivore
Omnivore
Feeding Based on Diet
Euryphagous
Mixed diet
Stenophagous
Limited number of food sources
Monophagous
Using only one food source
Descriptive Feeding Classification
Example: Stenophagous herbivore
Feeding classification is often associated with body form and digestive
anatomy
Feeding to Obtain Energy
Metabolic rate regulates food demand
Digestibility of food also dictates quantity
Friability = ease for fragmentation of food in the stomach
Prey Capture Methods
Ram feeding
Overtakes food with open mouth
Suction feeding
Rapid expansion of buccal cavity pulls food in
Manipulation
Biting, scraping, clipping, gripping, grasping
Tools for Getting Food to the Digestive System
Mouth (structure)
Teeth
Pharynx
Gill rakers
Mouth Structure
Size and placement is important to feeding method
Ancestral state = firm jaws and sharp teeth
Suction modification
Shortened jaw
Extensible buccal cavity
Biting fish have forward, blade-like teeth with well developed jaw
muscles
Teeth
Bones that can bear teeth
Premaxilla
Maxilla
Dentary
Palatine
Pterygoid
Vomer
Parasphenoid
Basibrachial
Glossohyal
Pharyngeal arch
Pharynx
Area of gill attachment
Connects mouth to esophagus
Includes the pharyngeal pad (in some fish)
Removes excess water from ingested food
Ways Teeth are Attached
Strong mineralized connection
Partial mineralization along with collagen
Hinged and depressible with base attachment not fully mineralized
Collagen attached to posterior base
Gill Rakers
Inwardly directed projections from gills
Aid in filtering food from water
Can aid in swallowing large food
Some fish have two sizes
Esophagus
Usually short & distensible
Many fish swallow large objects
For all the teeth, there is very little chewing
Walls have circular & longitudinal muscles
Most swallowing is by esophagus
Taste buds
Gastric glands in some fish
Modifications of Esophagus
Butterflyfish
Muscular sacs lined with teeth
Grind & crush food in esophogeal sacs
Some fish have the esophagus modified for respiration
Stomach
Differs greatly depending on diet
Various shapes
Bag-like
U-shaped
V-shaped
Stomach is absent in some fish
Lampreys, hagfish, minnows, & others
Intestine
Length is quite variable
Corresponds to amount of indigestible material in diet
Carnivores short
Herbivores several times body length
Some fish have a spiral intestine
Increases absorptive surface
Modifications of Intestine
Parasitic fish like lampreys
Intestine is very thin and expandable
Hagfish
Intestine with extensive folding
Ingest large food
No stomach
Cloaca
Some fish have a posterior gut that is a common canal for urinary
& reproductive systems
Sharks
Rays
lungfish
Digestive Accessory Organs
Organs associated with the intestine
Pyloric caeca
Liver
Pancreas
Swimbladder (in some fish)
Spleen (associated but not digestive)
Pyloric Caeca
Attaches beyond pyloric end of stomach
One to many blind sacs
Absent in some fish
Functions
Digestion
Absorption
Liver
Very large in all fish
Up to 30% of shark body mass
Lies over or surrounds the stomach
Most commonly bi-lobed
Most fish have bile duct & gall bladder
Function
Bile secretion
Glycogen storage
Other biochemical processes
Pancreas
Diffuse tissue in some fish
Combined with liver in some derived fish (hepatopancreas)
Hagfish have several pancreatic ducts that empty into bile duct
Secretes enzymes & insulin
Spleen
Usually on or behind stomach
Function
Red blood cell formation
Destruction of old blood cells
Agnatha have diffuse spleenlike tissue
Lungfish lack a spleen
Digestion in Fish
Breakdown by acidic secretions & enzymes
Many enzymes
Many food differences between species
Most digestion starts in stomach when present
Guidelines for Rate of Digestion
Carnivores have slow food passage
14-32 hours
Motility is very slow
Herbivores pass more food faster
<3 8 hours
A few species use fermentation for up to 20 hours
Absorption
Much the same as for mammals
Diffusion
Membrane transport proteins
Metabolism and Nutrition
Different species need different amounts of nutrition because there
is great variation in metabolism
General rule: Metabolism is directly influenced by temperature
Nutrient requirements
Proteins
Carbohydrates
Lipids
Minerals
Vitamins
water
Proteins
Protein requirements differ with age and temperature
Fry need more protein
Higher temps require more protein
Fish require 10 essential amino acids
High proteins are used in aquaculture
Carbohydrates
Omnivorous fish can substitute some carbs for proteins
Too many carbs can deposit excess glycogen in the liver
Lipids
Mostly broken down for energy source
Getting too much fat is uncommon from normal fish feeding
Some fats are toxic to fish
Vitamins & Minerals
Dietary requirements are poorly known
Need most materials as other vertebrates
Lack of certain substances often cause developmental deformities
Fish Growth
Fish continue to grow throughout their lives
Growth rate is a good indicator of fish health
I = M + G + E
I = ingested food energy
M = energy for metabolism
G =GROWTH
E = energy excreted
Factors Affecting Growth
Hormones
Growth hormone secreted by pituitary
Steroid hormones from gonads
Temperature
Most important environmental factor
Growth increases up to a point
Fish tend to prefer temperatures where their growth is maximal
Dissolved Oxygen
More is better
Ammonia
High concentrations slow growth
Salinity
Growth is altered when fish are not in their optimum salinity
Competition
Generally slows growth
Food
Availability & quality affect growth
Photoperiod
Longer days increase growth
Age & Maturity
Growth is rapid early in life
With maturity more energy is diverted to gonadal tissue
Larger fish need more energy to maintain body
Conditioning
Lecture 7
Fish Reproduction & Development
Fish Reproductive Strategies
Anatomical structure often reflects reproductive strategy
External gender differences are sometimes minimal
Internally there are obvious differences, but some similarities
Paired gonads
Most organs are found on the roof of the body cavity
Male Reproductive Organs
Testes
Smooth white organs
Can be up to 12% of body weight
After sperm leaves testes, there is a large variation of other organs
Male Reproductive Organs
Hagfish
Single elongate testes
Right side of body
Hermaphroditism is common
Sperm released into body cavity
Sperm pass through sinus to genital pore
Male Reproductive Organs
Lampreys
Single testis suspended by mesorchium
Fight side of intestine
Sperm shed into body cavity
Exit body via urogenital opening
Prominent urogenital papillae
Male Reproductive Organs
Sharks
Paired testes in anterior body cavity
Mesorchium present
Right testis usually larger than left
Sperm discharges into canal shared with kidney
Leydigs gland in kidney
Produces seminal fluid
Male Reproductive Organs
Shark continued
Duct system leaves kidney to carry sperm
Vas defrens
Seminal vesicle
Sperm sac
Sperm sac empties into urogenital sinus
Empties into cloaca
Sperm exits body via grooves of claspers
Male Reproductive Organs
Shark - continued
Claspers
Organ that attaches and holds onto female shark
Contains glandular sacs called siphons
Lubrication fluid
Male Reproductive Organs
Chimaeras
More complex system of ducts than sharks
Urogenital pore opens behind anus
Pelvic claspers release seminal fluid
Male Reproductive Organs
Bony fish
Paired testes lie long swimbladder
Usually no connection between reproductive and urinary system
Genital pore present
Duct system
Seminal vesicle usually absent
There are many exceptions (especially in primitive teleosts)
Female Reproductive Organs
Ovaries may make up 30-70% of body weight
Large variation in strategy for transfer of eggs after leaving the ovary
Female Reproductive Organs
Hagfish
Single ovary right of gut
Produce large eggs with tough shells & hooks
No oviducts
Single genital pore behind anus
Sinus interiorly
Female Reproductive Organs
Lampreys
Single ovary suspended by mesovarium
Eggs shed into body cavity
Exit via urogenital sinus
Small eggs
Some species may deposit up to 260,000
Female Reproductive Organs
Sharks
Paired ovaries
Left may be greatly reduced
Anterior body cavity
Suspended by mesovarium
Oviducts
Nidamental (shell) gland
Fertilization occurs here
Viviparous or ovoviviparous
Female Reproductive Organs
Chimaeras
Exceptions from sharks
Two oviducts separated to exterior
Nidamental gland followed by uterine portion of oviduct
Female Reproductive Organs
Bony fish
Oviducts from ovary to outside
Oviducts continuous with ovary
Large ovaries are sometimes fused
External Sexual Characters
Many fish have similar looking sexes
Dimorphism = differences in body shape
Size is most common difference
Breeding tubercles
Contact organs
Dichromatism = color differences of sexes
Some differences are only apparent at spawning
Fish Reproductive Strategies
Semelparity
One-time reproductive activity
Common in diadromous species
Species often have one generation per year
Fish Reproductive Strategies
Iteropaurous
Individuals spawn two to several times in a lifetime
Provides a better chance if the envrionment is unpredictable
Overlapping generations
Fish Reproductive Strategies
Nonguarders
Open substrate
Brood hiders
Guarders
Substrate choosers
Nest spawners
Bearers
External
Internal
Nonguarders
Do not protect eggs or young
Two methods
Scatter eggs in environment
Hide eggs and then leave
Nonguarders
Pelagic spawners
Common among marine fish
Spawn in open water
Many are schooling fish
Young become dispersed by water currents
Eggs & fry are buoyant
Oil globules present
High mortality
Large number of eggs
Nonguarders
Benthic spawners
Mostly freshwater
Eggs are usually adhesive
Rocks
Gravel
Pelagic or benthic larvae
Some larvae also attach
Nonguarders
Brood hiders
Hide eggs
No other parental care
Often bury eggs
Guarders
Eggs & Embryos attached to a location
Courtship behavior is often elaborate
Eggs most commonly guarded by males
Protection
Oxygen enhancement
Guarders
Two different groups
Nest spawners
Construct nest
Substrate choosers
No nest construction
Clean suitable area
Fry are usually also guarded
Bearers
Carry embryos
Externally
Pouch
Mouthbrooder
Internally
Fertilization is internal
Produce small numbers
Live-Bearing Fish
Retained ovipary
Some eggs still in female body get fertilized
Short embryonic development
Ovovivipary
Obligate internal fertilization of eggs
Eggs develop internally
Nourishment is from yolk
Live-Bearing Fish
Vivipary
Eggs fertilized internally
Nourishment is from mother
Mother may have several broods at any one time
Mate Finding
Selection is minimal in schooling fish
Many fish have an elaborate system
Color
Pattern
Sonic cues
Pheromones
Courtship behavior
Physiological Adaptations
In some species temperature (season) is responsible for stimulating
gonads
Several different things can be stimulated or inhibited with different
temperatures
Spermatogenesis
Vitellogenesis
Ovulation
Courtship behavior is often needed for ovulation
Hormonal Control of Reproduction
Gonadotropic releasing hormone (hypothalamus) & gonadotropic hormones
(pituitary) needed for gonad maturation
Gonadal steroid hormones
Estrogen stimulates production of vitellogenin
Vitellogenin regulates vitellogenesis
Progestin oocyte maturation
Other androgens secondary sexual characters, behavior
Fecundity of Fish
Measure of reproductive potential
Usually increases with size of female
Factors affecting fecundity
Fertility
Frequency of spawning
Parental care
Egg size
Population density
Environmental factors
Alternative Reproductive Strategies
Alternative male strategies
Jack males
Small males that sneak in to breed
Sneaking
Staying close to nest to dash in and release sperm
Satellite male
Resembles female and sneaks in to fertilize eggs
Alternative Reproductive Strategies
Hermaphroditism
Found in 14 families
Two types
Synchronous
Both gonads
Sequential
Change gonads
Often because of absence of dominant male
Alternative Reproductive Strategies
Parthenogenesis
Sperm not required for fertilization
Some need sperm from another species to activate development of eggs
Called sexual parasites
No chromosome exchange
Only uniform females are produced
Alternative Reproductive Strategies
Hybridogenesis
Species is only female
Eggs must be fertilized by another species
Chromosomes from male are lost during mitosis
Fish embryology
Only one sperm can fertilize an egg
True even if more enter
Most eggs have a good supply of yolk
Incubation is usually temperature dependent
Hatching is often aided by glandular secretions
Weaken or liquefy chorion
Early Life History
Stages after hatching
Yolk sac larvae
Preflexion larvae
Flexion larvae
Postflexion larvae
Juvenile Period
Often a distinct metamorphosis from larval characters
Begins when organ systems are fully formed
Lasts until gonads become mature
Lecture 8
Fish Senses
Central Nervous System
Great variation in fish brain morphology
Size varies
Senses account for most size variation
Range from 0.1% of body weight (coelacanth) to over 1% (Mormyridae)
Brain Development
First develops into 3 sections
Forebrain = prosencephalon
Midbrain = mesencephalon
Hindbrain = rhombencephalon
Brain Structure
Cerebrum = Telencephalon
Thalamus = Diencephalon
Tectum = Mesencephalon
Cerebellum & Pons = Metencephalon
Medulla Oblongata = Myelencephalon
The major portion of the telencephalon deals with olfaction
Diencephalon
Nerve tracts
Pituitary
Pineal gland
Light sensitive
Parapineal gland
Optic chiasm crosses externally
Tectum
= optic tectum
= midbrain
= mesencephalon
Optic lobes are prominent feature
Size of optic lobes is associated with how visual the fish is
Metencephalon
Cerebellum is involved in muscle coordination
Nerve conduction tracts in pons
Also some autonomic reflex centers
Metencephalon
Medulla has many reflex centers
Example = startle reflex
There is Great Variation in Fish Brains
Eye Structure
Structure very much like other vertebrates
Cornea
Sclera
Lens
Conjunctiva
Iris
Choroid layer
Retina
Vitreous & aqueous chambers
Visual Cells of Fish Eyes
Rods
Dominate in deep dwelling fish
Cones
Sometimes long & short
Double cones
Maximum absorbance range of fish eyes
Some down to 360nm (UV)
Some up to 625 nm (red)
Problems Associated with Aquatic Vision
Less light enters water
Water disturbances change angle of incidence
Some species rely on seeing out of the water to locate prey
Protection for Eyes
Eyelids are well developed in some elasmobranchs
Eyes can not bulge
Cornea is often made of four layers
Multicellular epithelium
Collagenous stroma
Descemets membrane
Endothelium
Differences Among Fish Eyes
Placement
Sides of head
Most common
Wide lateral fields of vision
No binocular vision
Eyes set forward
Eyes set upward
Extra eye monitors area below
Stalked eyes
A few fish have eyes capable of terrestrial and/or aquatic viewing
Some fish have vestigial eyes or lack eyes
Importance of Eyes
Some fish are very visual
In many fish, vision is not the primary sense
Some fish are blind
Hearing in Fish
Lateralis system
Auditory
Mechanosensory
Electrosensory
Organs
Inner ear
Lateral line system
Ampullary organs
Inner Ear
Osseous labyrinth in bony fish
Membranous labrynth within bony
Distinct chambers
Sacculus
Utricus
Lagena
Semicircular canal ampullae
Mechanics of inner ear
Hair cells
Otoliths
Sacculus & Lagena function as sound organs
Utricus & canals are for equilibrium
Hearing in Fish
Sound energy is compression waves
Water denser than air
Low frequency sound propogation is easy in water
Having a connection between swimbladder & ear makes range more
sensitive
Fish Equilibrium
Movement is sensed by moving otoliths across hair cells
Lateral Line System
Detects movements of water
Can detect anything moving around them
Lateral Line System
Neuromasts in canals and skin
Contain hair cells
Respond to deformation by mechanical forces
Electrosensory System
Some fish produce weak electric currents
Electric currents can be detected by special organs
Some fish that do not produce electricity still can sense it
Detection of Electric Current
Ampullae of Lorenzini
Located in skin
Can become insensitive to prolonged stimulation
Using Electric Currents
Location of objects
Communication
Navigation
Fish hold their bodies straight and undulate to receive electric
stimulation
Chemical Senses
Olfaction
Gustation
Some fish have other chemosensory receptors
Olfaction
Sense of smell
Uses for olfaction
Detection of food
Orientation
Sensing pheromones as reproductive cues
Avoiding predators
Organs for Olfaction
Organs are in sacs or pits on the anterior head
In front of eye in teleosts
In front of mouth in elasmobranchs
Receptor cells in epithelium
Nares often apparent
Location of Nares
Olfactory Receptor Cells
Usually rosettes of cells
Have distinct pattern representative of species
Most receptors are in externally opening sacs, some have openings
to the pharynx
Detection of Food
Several different chemicals are sensed
Blood
Fish oils
Other specializes cues
Orientation by Olfaction
Smell home
Some smells are imprinted
Soils
Vegetation type
Pheromones released in feces
Gustation
Taste
Taste buds
Specialized epithelial cells
Location
Pharynx
Mouth
Gill arches
Uses for Tasting
Evaluate food
Sensing different sources
Other Chemosensory Receptors
Solitary chemosensory cells
Epidermis
Sense salts, acids, alkaline materials
Modified pectoral fins
In place of taste buds in a few fish
Lecture 9
Fish Behavior & Communication
Fish Behaviors
Migration
Shoaling
Feeding
Aggression
Resting
Communication
Fish Migration
Fish migrations are usually round-trip
Reasons for migration
Food gathering
Temperature adjustment
Breeding
Timing of migrations
Annual
Daily
generational
Classification of Fish Migration
Diadromous Travel between sea & fresh water
Anadromous most of life at sea, breed in fresh water
Catadromous most of life in fresh water, breed at sea
Amphidromous migrate between water types at some stage other than
breeding
Diadromous Travel between sea & fresh water
Potamodromous Migrate within a fresh water system
Ocenodromous Migrate to different regions of the ocean
Reasons for Migrations
Take advantage of different habitats
Feeding
Protection
Avoid adverse conditions
Meet requirements for reproduction
Orientation During Migration
Orientation to gradients of temperature, salinity, and chemicals
Orientation by the sun
Orientation to geomagnetic and geoelectric fields
Disadvantages of Migrations
Expenditure of energy
Most must store energy before migration
Risk from predation
Adjustments Required Due to Migrations
Adjusting physiologically to new water conditions
Temperature
Light
Water chemistry
Many migratory species are now rapidly declining due to changes caused
by man
Comparison of Migrations
Some stream species migrate a few yards from feeding to spawning
grounds
Some species travel hundreds of miles just to spawn
Shoals and Other Aggregations
Forms of fish grouping
Solitary
Shoal
School
Pod
Reasons for grouping
Traveling
Feeding
Dealing with predators
Reproduction
Shoaling
A social grouping of fish
Occurs throughout life in about 25% of fish species
Half of all fish shoal at some time
Benefits of Shoaling
Gives a predator many moving targets
Confuses predators
Increases chances at the individual level
Increases food finding ability
Keeps potential mates in close proximity
Schooling
Polarized, synchronized group
Has direction
Has reason for grouping
Precise, structured movement
Vision use is enhanced
Uses of Schooling
Traveling
Some hydrodynamic advantage
Planktivorous feeding
Encirclement of predator
Streaming to avoid a predator
Pods
Tightly grouped school
Move as a single unit (including making quick turns)
Makes the school appear like one large organism
Protection from predators
Liabilities of Grouping Behavior
Increased likelihood of disease & parasite transmission
Becoming more conspicuous to some predators
Harvested more easily by man
Feeding Behavior
Morphology is often a key to feeding behavior many fish have specialized
habits
Actual feeding may depend on what is available
Optimal foraging Take whatever is closest, as long as it is suitable
food
Highest quality of food for the least amount of effort
Optimal Foraging
All else being equal, take the largest prey
Dont choose prey that takes more energy than it provides
Be in a habitat that provides the type of food you are looking for
Risk Sensitive Foraging
Foraging is sometimes restricted because of undo risk
It does not make sense to look for prey where you will become the
prey
Must balance energy gain possibility with risk of obtaining the energy
Finding Food
Visual detection
Diurnal feeders
Means being in the open in bright light
Olfaction
Common in bottom dwelling species
Taste
Aggressive Behavior
Direct charges
Often includes biting
Ritualistic displays
Modified swimming
Flaring gill covers
Color changes
Threatening movements
Reasons for Aggressive Behavior
Defense of territory
Usually connected with reproduction
Sometimes to keep food source
Defense of brood
Repelling competitors for mates
Resting Behavior
Inactive state
Some fish spend a large part of the day not doing anything
Many species change color patterns
Most fish rest on or near the substrate
Many fish have a specified time of day when resting takes place
Some fish never rest
Must keep moving
Communication
Visual signals
Auditory signals
Chemical signals
Electric signals
Visual Signals
Most important communication signal
Large variety of signals
Different species use different languages
Some cues are recognized between species
How visual signals are produced
Types of coloring
Pigments
Colored compounds
Located in chromatophores
In mostly in skin, but also in eyes & organs
Controlled by hormones & nerves
Structural colors
Reflection of light
Kinds of Pigments in Fish
Carotenoid pigments
Bright reds & yellow
Green when they overly blue structural color
Melanins
Dark red, brown, black
Purines (guanine)
Colorless crystals responsible for some structural colors
Purpose of Color Patterns
Thermoregulatin
Probably not very significant
Intraspecific communication
Evasion of predators
Common Color Patterns
Red coloration
Poster colors
Disruptive colors
Countershading
Eye ornamentation
Lateral stripes
Polychromatism
Red Coloration
Red fish are common
Cryptic color in low light
Blends in to red algae
Used in spawning fish
Recognized at short distances
Does not attract predators at long distance
Poster Colors
Bright, complex color patterns
Some fish use this to advertise when protecting territories
May serve to signal shoal
In some cases it may be used for predator avoidance
Blending into a complex background
Flash effect to avoid predators
May serve as a warning to others
Disruptive Coloration
Disrupt the outline of the fish
Make them less visible
Often associated with beds of plants
Countershading
Being dark on top, light on bottom
Look like substrate from above
Look like water surface from below
Eye Ornamentation
Either to disguise the eye or emphasize it
Disguising the eye
Minimize contrasting color
Field of spots around eye to disguise pupil
Eye lines that match pupil
Emphasizing the eye
Pattern or colors in eye
Usually used for interspecific signaling
Eye Spots
Usually at base of caudal fin
Usually used to confuse predators
Common in some fry
Sometimes used for species recognition
Lateral Stripes
Mid-lateral band usually
Best developed in schooling fish
Keep school oriented while confusing predators
Makes it hard to pick out individuals
Polychromatism
Dominant members are often more brightly colored
Makes it easier to attract mates
But, makes them more conspicuous to predators
Auditory Signals
Most fish produce sounds
Uses for sound
Courtship singing
Territorial defense
Signaling shoal
Sound Production
Stridulation
Rubbing hard surfaces together
Low frequency sounds
Vibration of swimbladder
Can give loud croaking
Incidental to other activities
Chemical Signals
Pheromones released into the water
Reproductive cues
Recognition
Schreckstoff = fear scents
Predator avoidance
Produced in epidermal cells
Electrical Signals
Muscle contractions give off a weak
Some fish have electric producing organs
Used to locate prey or conspecifics