Sensory Systems, Behavior, Reproduction
Biology of Fishes
11.1.12
Overview
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Presentations & Other Assignments
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Presentation Guidelines – online Friday
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Guest Lecture II – Fishes of the Great Lakes 11.8.2012
Syllabus Revisions
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Exam II – November 20
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Upcoming Topics
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Sensory Systems
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Behavior
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Reproduction
Sensory Systems
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What fishes use to gather information about their
environment
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Accurate and up-to-date information about
surrounding conditions
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Critical to decision-making success in feeding,
predator-avoidance, mate selection
Sensory Systems
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Mechanoreception
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Involves detection of movement
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2 major systems
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Lateral line
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Inner ear
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Collectively referred to as the “acoustico-lateralis”
system
Sensory Systems
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Lateral line
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Unique sense organ found in all fishes (except hagfish) and
some amphibians
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Adapted for life in aquatic environments
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Sensory system stimulated mechanically by motion
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weak water currents hitting the body result in distinct fin
movements
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Local cauterization of lateral line results in no fin movements
Sensory Systems
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Lateral line – Structure
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Basic unit that senses motion is the neuromast
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Neuromast consists of cupula – jelly-like substance and
sensory hair cells
Sensory Systems
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Lateral line – Structure
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Basic unit that sense motion is the neuromast
Sensory Systems
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Lateral line – Structure
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Basic unit that senses motion is the neuromast
Sensory Systems
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Lateral line – Structure
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2 types of neuromast
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Superficial neuromast
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Located on surface, distributed on head and body
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Tend to be smaller and have fewer hair cells
Canal neuromasts
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Located in canals in head and along body (lateral line)
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Tend to be larger and have more hair cells
Sensory Systems
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Lateral line – Structure
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Superficial neuromast
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Canal neuromasts
Sensory Systems
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Lateral line – function
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Identify and locate stationary object
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Prey detection – (e.g. sculpin-zooplankton, pike-fishes, terrestrial
insects)
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Detect flow differences (maintaining position, prey detection –
candiru catfish)
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Communicate for spawning synchronization
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Synchronized swimming – schools (even blind fishes can school)
blind cave fish
Sensory Systems
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Inner Ear
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Also used for mechanoreception
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Provides information on the orientation and movement of
a fish
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Critical for maintaining balance and position
Sensory Systems
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Inner Ear – structure
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Semicircular canals
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Filled with fluid (endolymph)
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Movement of the fish causes movement of fluid in semicircular
canals
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Enlarged area (ampulla) contains sensory hair cells that are
displaced by movement of fluid
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Movement of hair cells results in changes response of sensory
neurons – provides brain with information on changes in
acceleration and orientation
Sensory Systems
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Inner Ear – structure
Sensory Systems
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Inner Ear – structure
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Otoliths
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Ear “bones” or “stones” actually crystalline formation
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Provide information on orientation and movement
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Can be used in aging fishes
Sensory Systems
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Inner Ear – structure
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Otoliths
Sensory Systems
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Hearing
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Inner ear also responsible for hearing
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Most fish tissue transparent to sound – density of tissue is similar to
water
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Sound vibrations travel right through the fish
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Otoliths denser – vibrate for sound detection
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Otolith vibration sets hair cells in motion – changes response of
neurons
Sensory Systems
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Hearing – Gas Bladder
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Also increases sensitivity to sound
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Sound waves cause vibrations in gas bladder – transmitted to inner
ear
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Weberian apparatus (Otophysi)
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Clupeomorpha have extensions of gas bladder that lie next to inner
ear
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Other fishes – gas bladder lies close enough to increase sensitivity
Behavior
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Sum of all motor responses to all internal and external
stimuli
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Fishes exhibit a host of behaviors associated with
feeding, predator-avoidance, reproduction, locomotion,
interactions
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Behaviors are plastic – vary with life stage, season, time
of day, environment, perceived risks; also individuals,
populations
Behavior
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Dynamic displays – involve posturing
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Ways of communicating to one another – courtship, territory defense,
dominance, signaling to young
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Include visual displays – rapid change in color, exposure of colored
structures, mouth/gill flaring, fin flicking, raising fins
Behavior
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Dynamic displays – involve posturing
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Lateral displays (cichlids, anemone fishes)
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Frontal displays (kissing gouramis, some cichlids)
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Communication via sound, chemicals (alarm substance), touch,
electricity
Behavior
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Parental Care – association between parent and
offspring after fertilization that enhances survivorship
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Increases survival by reducing predation risk, increasing food access
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Many fishes provide no parental care – egg dispersers, pelagic eggs
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Some parental care is common among fishes
% of families showing parental care
Taxon
Male care
Female care
Both parents
No care
Mammals
0
90
10
0
Birds
2
8
90
0
Non teleosts
6
66
0
28
Teleosts
11
7
4
78
Behavior
% of families showing parental care
Taxon
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Male care
Female care
Both parents
No care
Mammals
0
90
10
0
Birds
2
8
90
0
Non teleosts
6
66
0
28
Teleosts
11
7
4
78
Unlike other vertebrates, males are most common care-giver
in fishes
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Females invest +energy in egg production; guarding would reduce
amount of future reproduction
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Paternity assurance – makes sure only one is fertilizing eggs
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Tradeoff – costs energy and reduces fecundity
Behavior - Parental Care
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Two types – behavioral or physiological
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Substrate guarding
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Most common
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Male constructs nest; guards, fans, cleans eggs – may also guard young
(catfishes, minnows, sculpin, stickleback, bowfin, SA lungfish)
Mouth brooding
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External egg-carrying
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Eggs and sometimes young carried in mouth (lumpfishes, gouramis, arowanas,
cichlids
Eggs carried on lower lip, on head, or own belly (several catfishes)
Brood pouch
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Carried inside pouch of male – seahorses and pipefishes
Behavior - Parental Care
Behavior
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The most obvious form of social behavior in fishes is the
formation of groups
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Shoals – unorganized grouping of fishes
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Similar to a flock of birds
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May gather together to feed, breed, or seek refuge (salmon, gars,
minnows)
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Basically “milling around”, no organized or coordinated swimming
Schools – synchronized swimming groups – exhibit
coordinated behaviors
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One of the behaviors exhibited by fish in shoals
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In N. American literature “school is used to cover both shoaling
(unorganized) and schooling (organized)
Behavior
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Schools – Why do they form?
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Fish act as individuals – don’t school for the benefit of the group
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“selfish” – ensure access to food, minimize predation
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Hydrodynamic advantage – save energy by drafting – many studies,
but little solid evidence that fish save energy by schooling
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Most likely relate to foraging and predator avoidance
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Foraging
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Find food faster
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Prey capture may be easier
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Hunting in packs (tuna, sailfish)
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Tradeoff – must compete with individuals of group
Behavior
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Schools – Why do they form?
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Anti-predator strategy – the need to avoid predation is a major
selective force that shapes schooling behavior (takes precedence over
finding a meal)
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Evasion – attack success of predators declines with group size;
most likely due to confusion of predator
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Compaction – in presence of predator, group becomes more
compact and cohesive
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Detection – many eyes aid in predator detection
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Skittering – minnows detect predator and leap out of water then
return to school – may alert others in school, triggering anti-predator
behavior
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Predator inspection – fishes (usually small groups) approach
predator
Behavior
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Schools – Why do they form?
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Reproduction
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Increases likelihood of finding a mate
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Coordinates readiness (maturity) through hormonal & behavioral
cues
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Facilitates arrival at spawning site at correct time (fish migrations
– salmon, whitefish, mullet)
Reproduction
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Fishes – most diverse group of vertebrates – incredibly
diverse reproductive strategies/mechanisms
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Reproductive strategies are adaptations to maximize the
fitness of individuals – ensure genes are passed on
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Overview of fish mating systems
Reproduction
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Frequency of spawning
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Iteroparity (iteroparous)
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More than one spawning during a lifetime
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Most fishes use this strategy
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K-selected species – grow slowly, reproduce late, produce fewer
young, longer life expectancy, lower reproductive effort (spread
across time), may provide parental care
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Stable, predictable habitats – survival to following year is high
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Lower fecundity, but spread out to ensure some reproduction
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~25-60% of somatic energy used for reproduction
Reproduction
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Frequency of spawning
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Semelparity (semelparous)
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Spawn once and die
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Diadromous or highly migratory fishes tend to be semelparous
(salmon, lamprey, anguillid eels)
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R-selected species – grow fast, reproduce early, produce many
young, shorter life expectancy, high reproductive effort (“big
bang”), no parental care
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Unstable/unpredictable environments – high mortality
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Place eggs and young in ideal growing conditions
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Overwhelm predators
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~60-85% somatic energy used for reproduction
Reproduction
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Modes of spawning
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Oviparous – fish lay eggs that are fertilized externally, mother
provides no nutrition other than yolk (most fishes)
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Ovoviviparous – eggs are retained in female and fertilized
internally, mother provides no nutrition (most sharks, coelacanth,
some poeciliids)
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Viviparous – eggs retained in female, fertilized internally, mother
provides nutrition (some sharks, goodeids, poeciliids)
Reproduction
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Types of fertilization
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External
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Most fishes
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Less time and energy spent in courtship
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Increase number of potential mates
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higher fecundity – more offspring produced
Internal
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Few groups of fishes
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Chondrichthyes, guppies, mollies
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Requires lengthy courtship
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Intromittent organ – transfer sperm to females (claspers, modified
anal fin)
Reproduction
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Mating Systems
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Promiscuous – no obvious mate choice – both spawn with multiple
partners
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Polygamy – only one sex has multiple partners
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Polyandry – one female, several males
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Relatively uncommon
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Anemonefish, anglerfishes, gars
Polygyny – one male, multiple females
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Most common
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Territorial males care for eggs/young – visited by multiple
females (sculpins, sunfishes, darters, damselfishes some
cichlids); harems may also form
Reproduction
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Mating Systems
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Monogamy – fish mate exclusively with same individual
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N.American freshwater catfishes, butterflyfishes, some
cichlids, seahorses
Reproduction
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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
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Simultaneous – capable of releasing viable eggs and sperm
during same spawning
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Some can self-fertilize (Cyprinodontiform Rivulus); likely
adaptation to lower population size, isolated habitats
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Alternate sex roles during spawning (Serranus); male with harem
of hermaphrodite females – male removed, largest hermaphrodite
female changes into male
Reproduction
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Gender Systems – some fishes are hermaphrodites and can
function as males and/or females
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Sequential – function as one sex for part of their life, then
switch
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Protogynous (protogyny) – start female, change to male; more
common
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Protandrous (protandry) – start male, change to female; less
common
Parthenogenetic – alternative to traditional gender roles
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All female but require sperm from other species to activate cell
division in eggs (genetic info from males is not conserved)
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Produce daughters genetically identical to mother (Poeciliidae in
TX and Mexico)