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Sensory Systems, Behavior, Reproduction Biology of Fishes 11.1.12. Overview. Presentations & Other Assignments Presentation Guidelines – online Friday Guest Lecture II – Fishes of the Great Lakes 11.8.2012 Syllabus Revisions Exam II – November 20 Upcoming Topics Sensory Systems Behavior

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  • Presentations & Other Assignments

    • Presentation Guidelines – online Friday

    • Guest Lecture II – Fishes of the Great Lakes 11.8.2012

  • Syllabus Revisions

    • Exam II – November 20

    • Upcoming Topics

  • Sensory Systems

  • Behavior

  • Reproduction

Sensory systems
Sensory Systems

What fishes use to gather information about their environment

Accurate and up-to-date information about surrounding conditions

Critical to decision-making success in feeding, predator-avoidance, mate selection

Sensory systems1
Sensory Systems

  • Mechanoreception

    • Involves detection of movement

    • 2 major systems

      • Lateral line

      • Inner ear

      • Collectively referred to as the “acoustico-lateralis” system

Sensory systems2
Sensory Systems

  • Lateral line

    • Unique sense organ found in all fishes (except hagfish) and some amphibians

    • Adapted for life in aquatic environments

    • Sensory system stimulated mechanically by motion

      • weak water currents hitting the body result in distinct fin movements

      • Local cauterization of lateral line results in no fin movements

Sensory systems3
Sensory Systems

  • Lateral line– Structure

    • Basic unit that senses motion is the neuromast

    • Neuromast consists of cupula – jelly-like substance and sensory hair cells

Sensory systems4
Sensory Systems

  • Lateral line– Structure

    • Basic unit that sense motion is the neuromast

Sensory systems5
Sensory Systems

  • Lateral line– Structure

    • Basic unit that senses motion is the neuromast

Sensory systems6
Sensory Systems

  • Lateral line– Structure

    • 2 types of neuromast

      • Superficial neuromast

        • Located on surface, distributed on head and body

        • Tend to be smaller and have fewer hair cells

      • Canal neuromasts

        • Located in canals in head and along body (lateral line)

        • Tend to be larger and have more hair cells

Sensory systems7
Sensory Systems

  • Lateral line– Structure

    • Superficial neuromast

    • Canal neuromasts

Sensory systems8
Sensory Systems

blind cave fish

  • Lateral line – function

    • Identify and locate stationary object

    • Prey detection – (e.g. sculpin-zooplankton, pike-fishes, terrestrial insects)

    • Detect flow differences (maintaining position, prey detection – candiru catfish)

    • Communicate for spawning synchronization

    • Synchronized swimming – schools (even blind fishes can school)

Sensory systems9
Sensory Systems

  • Inner Ear

    • Also used for mechanoreception

    • Provides information on the orientation and movement of a fish

    • Critical for maintaining balance and position

Sensory systems10
Sensory Systems

  • Inner Ear – structure

    • Semicircular canals

      • Filled with fluid (endolymph)

      • Movement of the fish causes movement of fluid in semicircular canals

      • Enlarged area (ampulla) contains sensory hair cells that are displaced by movement of fluid

      • Movement of hair cells results in changes response of sensory neurons – provides brain with information on changes in acceleration and orientation

Sensory systems11
Sensory Systems

Inner Ear – structure

Sensory systems12
Sensory Systems

  • Inner Ear – structure

    • Otoliths

      • Ear “bones” or “stones” actually crystalline formation

      • Provide information on orientation and movement

      • Can be used in aging fishes

Sensory systems13
Sensory Systems

  • Inner Ear – structure

    • Otoliths

Sensory systems14
Sensory Systems

  • Hearing

    • Inner ear also responsible for hearing

    • Most fish tissue transparent to sound – density of tissue is similar to water

    • Sound vibrations travel right through the fish

    • Otoliths denser – vibrate for sound detection

    • Otolith vibration sets hair cells in motion – changes response of neurons

Sensory systems15
Sensory Systems

  • Hearing – Gas Bladder

    • Also increases sensitivity to sound

    • Sound waves cause vibrations in gas bladder – transmitted to inner ear

    • Weberian apparatus (Otophysi)

    • Clupeomorpha have extensions of gas bladder that lie next to inner ear

    • Other fishes – gas bladder lies close enough to increase sensitivity


Sum of all motor responses to all internal and external stimuli

Fishes exhibit a host of behaviors associated with feeding, predator-avoidance, reproduction, locomotion, interactions

Behaviors are plastic – vary with life stage, season, time of day, environment, perceived risks; also individuals, populations


  • Dynamic displays – involve posturing

    • Ways of communicating to one another – courtship, territory defense, dominance, signaling to young

    • Include visual displays – rapid change in color, exposure of colored structures, mouth/gill flaring, fin flicking, raising fins


  • Dynamic displays – involve posturing

    • Lateral displays (cichlids, anemone fishes)

    • Frontal displays (kissing gouramis, some cichlids)

    • Communication via sound, chemicals (alarm substance), touch, electricity


% of families showing parental care

  • Parental Care – association between parent and offspring after fertilization that enhances survivorship

    • Increases survival by reducing predation risk, increasing food access

    • Many fishes provide no parental care – egg dispersers, pelagic eggs

    • Some parental care is common among fishes


% of families showing parental care

  • Unlike other vertebrates, males are most common care-giver in fishes

    • Females invest +energy in egg production; guarding would reduce amount of future reproduction

    • Paternity assurance – makes sure only one is fertilizing eggs

    • Tradeoff – costs energy and reduces fecundity

Behavior parental care
Behavior - Parental Care

  • Two types – behavioral or physiological

  • Substrate guarding

    • Most common

    • Male constructs nest; guards, fans, cleans eggs – may also guard young (catfishes, minnows, sculpin, stickleback, bowfin, SA lungfish)

  • Mouth brooding

    • Eggs and sometimes young carried in mouth (lumpfishes, gouramis, arowanas, cichlids

  • External egg-carrying

    • Eggs carried on lower lip, on head, or own belly (several catfishes)

  • Brood pouch

    • Carried inside pouch of male – seahorses and pipefishes


  • The most obvious form of social behavior in fishes is the formation of groups

  • Shoals – unorganized grouping of fishes

    • Similar to a flock of birds

    • May gather together to feed, breed, or seek refuge (salmon, gars, minnows)

    • Basically “milling around”, no organized or coordinated swimming

  • Schools – synchronized swimming groups – exhibit coordinated behaviors

    • One of the behaviors exhibited by fish in shoals

    • In N. American literature “school is used to cover both shoaling (unorganized) and schooling (organized)


  • Schools – Why do they form?

    • Fish act as individuals – don’t school for the benefit of the group

      • “selfish” – ensure access to food, minimize predation

    • Hydrodynamic advantage – save energy by drafting – many studies, but little solid evidence that fish save energy by schooling

    • Most likely relate to foraging and predator avoidance

    • Foraging

      • Find food faster

      • Prey capture may be easier

      • Hunting in packs (tuna, sailfish)

      • Tradeoff – must compete with individuals of group


  • Schools – Why do they form?

    • Anti-predator strategy – the need to avoid predation is a major selective force that shapes schooling behavior (takes precedence over finding a meal)

      • Evasion – attack success of predators declines with group size; most likely due to confusion of predator

      • Compaction – in presence of predator, group becomes more compact and cohesive

      • Detection – many eyes aid in predator detection

        • Skittering – minnows detect predator and leap out of water then return to school – may alert others in school, triggering anti-predator behavior

        • Predator inspection – fishes (usually small groups) approach predator


  • Schools – Why do they form?

    • Reproduction

      • Increases likelihood of finding a mate

      • Coordinates readiness (maturity) through hormonal & behavioral cues

      • Facilitates arrival at spawning site at correct time (fish migrations – salmon, whitefish, mullet)


Fishes – most diverse group of vertebrates – incredibly diverse reproductive strategies/mechanisms

Reproductive strategies are adaptations to maximize the fitness of individuals – ensure genes are passed on

Overview of fish mating systems


  • Frequency of spawning

    • Iteroparity (iteroparous)

      • More than one spawning during a lifetime

      • Most fishes use this strategy

      • K-selected species – grow slowly, reproduce late, produce fewer young, longer life expectancy, lower reproductive effort (spread across time), may provide parental care

      • Stable, predictable habitats – survival to following year is high

      • Lower fecundity, but spread out to ensure some reproduction

      • ~25-60% of somatic energy used for reproduction


  • Frequency of spawning

    • Semelparity (semelparous)

      • Spawn once and die

      • Diadromous or highly migratory fishes tend to be semelparous (salmon, lamprey, anguillid eels)

      • R-selected species – grow fast, reproduce early, produce many young, shorter life expectancy, high reproductive effort (“big bang”), no parental care

      • Unstable/unpredictable environments – high mortality

      • Place eggs and young in ideal growing conditions

      • Overwhelm predators

      • ~60-85% somatic energy used for reproduction


  • Modes of spawning

    • Oviparous – fish lay eggs that are fertilized externally, mother provides no nutrition other than yolk (most fishes)

    • Ovoviviparous – eggs are retained in female and fertilized internally, mother provides no nutrition (most sharks, coelacanth, some poeciliids)

    • Viviparous – eggs retained in female, fertilized internally, mother provides nutrition (some sharks, goodeids, poeciliids)


  • Types of fertilization

    • External

      • Most fishes

      • Less time and energy spent in courtship

      • Increase number of potential mates

      • higher fecundity – more offspring produced

    • Internal

      • Few groups of fishes

      • Chondrichthyes, guppies, mollies

      • Requires lengthy courtship

      • Intromittent organ – transfer sperm to females (claspers, modified anal fin)


  • Mating Systems

    • Promiscuous– no obvious mate choice – both spawn with multiple partners

    • Polygamy– only one sex has multiple partners

      • Polyandry – one female, several males

        • Relatively uncommon

        • Anemonefish, anglerfishes, gars

      • Polygyny – one male, multiple females

        • Most common

        • Territorial males care for eggs/young – visited by multiple females(sculpins, sunfishes, darters, damselfishes some cichlids); harems may also form


  • Mating Systems

    • Monogamy – fish mate exclusively with same individual

      • N.American freshwater catfishes, butterflyfishes, some cichlids, seahorses


  • Gender Systems – in most fishes the sex of an individual is determined at early stage and fixed; some fishes are hermaphrodites and can function as males and/or females

    • Simultaneous – capable of releasing viable eggs and sperm during same spawning

      • Some can self-fertilize (CyprinodontiformRivulus); likely adaptation to lower population size, isolated habitats

      • Alternate sex roles during spawning (Serranus); male with harem of hermaphrodite females – male removed, largest hermaphrodite female changes into male


  • Gender Systems – some fishes are hermaphrodites and can function as males and/or females

    • Sequential – function as one sex for part of their life, then switch

      • Protogynous (protogyny) – start female, change to male; more common

      • Protandrous (protandry) – start male, change to female; less common

    • Parthenogenetic – alternative to traditional gender roles

      • All female but require sperm from other species to activate cell division in eggs (genetic info from males is not conserved)

      • Produce daughters genetically identical to mother (Poeciliidae in TX and Mexico)