Fish Biology - Lecture Outlines

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
– -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 Agassiz’s 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

• 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

(laterally compressed)
• Capable of quick bursts of speed
• Not in constant motion
• Predatory fish

(flattened dorsoventrally)
• Bottom-dwelling fish
• A few are adapted to swim in open water
• Large pectoral fins for movement

• 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

• Extreme version of eel-shape
• Largest part of body is the head

• Eel-like, but compressed

• Often lie-in-wait predators
• Most are piscivores
• Use quick burst of speed to emerge from hiding place
• Dorsal fin near caudal peduncle

• Body has length about equal to width

• Caudal area is narrowed to posterior point
• Usually found in deep-sea
• Mostly scavengers

• 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 water’s 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

• Type, size, and number tell a lot about a fish’s 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

• 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

• 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
• 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

• Less abundant than erythrocytes
• Provide a mechanism for blood clotting
• Rid the body of foreign materials
• Several different types

• Can vary in size
• Cell dominated by nucleus
• Important for immune system via antibody production
• There may be some phagocytic activity

• Cell outline may be quite irregular
• Phagocytes of foreign particles
• Attracted to foreign substances
• Use pseudopods to engulf antigens

• 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

• 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

• 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 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

• 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

• 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
• 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

• Bones that can bear teeth
– Premaxilla
– Maxilla
– Dentary
– Palatine
– Pterygoid
– Vomer
– Parasphenoid
– Basibrachial
– Glossohyal
– Pharyngeal arch

• 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

• 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

• Differs greatly depending on diet
• Various shapes
– Bag-like
– U-shaped
– V-shaped
• Stomach is absent in some fish
– Lampreys, hagfish, minnows, & others

• 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
• 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

• 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

• 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

• 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

• 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

• 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

• Omnivorous fish can substitute some carbs for proteins
• Too many carbs can deposit excess glycogen in the liver

• 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
– 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
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
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
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
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
Organ that attaches and holds onto female shark
Contains glandular sacs called siphons
Lubrication fluid
Male Reproductive Organs
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
Single ovary right of gut
Produce large eggs with tough shells & hooks
No oviducts
Single genital pore behind anus
Sinus interiorly
Female Reproductive Organs
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
Paired ovaries
Left may be greatly reduced
Anterior body cavity
Suspended by mesovarium
Nidamental (shell) gland
Fertilization occurs here
Viviparous or ovoviviparous
Female Reproductive Organs
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
One-time reproductive activity
Common in diadromous species
Species often have one generation per year
Fish Reproductive Strategies
Individuals spawn two to several times in a lifetime
Provides a better chance if the envrionment is unpredictable
Overlapping generations

Fish Reproductive Strategies
Open substrate
Brood hiders

Substrate choosers
Nest spawners
Do not protect eggs or young
Two methods
Scatter eggs in environment
Hide eggs and then leave
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
Benthic spawners
Mostly freshwater
Eggs are usually adhesive
Pelagic or benthic larvae
Some larvae also attach
Brood hiders
Hide eggs
No other parental care
Often bury eggs
Eggs & Embryos attached to a location
Courtship behavior is often elaborate
Eggs most commonly guarded by males
Oxygen enhancement
Two different groups
Nest spawners
Construct nest
Substrate choosers
No nest construction
Clean suitable area
Fry are usually also guarded
Carry embryos
Fertilization is internal
Produce small numbers
Live-Bearing Fish
Retained ovipary
Some eggs still in female body get fertilized
Short embryonic development
Obligate internal fertilization of eggs
Eggs develop internally
Nourishment is from yolk
Live-Bearing Fish
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
Sonic cues
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
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
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
Staying close to nest to dash in and release sperm
Satellite male
Resembles female and sneaks in to fertilize eggs
Alternative Reproductive Strategies
Found in 14 families
Two types
Both gonads
Change gonads
Often because of absence of dominant male
Alternative Reproductive Strategies
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
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
– Descemet’s 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

• 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

• 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

• 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

• 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

• 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
• Don’t 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

• 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

• 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

• 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