Sensory Systems, Behavior, ReproductionBiology of Fishes

11.1.12

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

Overview

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 Systems

Mechanoreception Involves detection of movement 2 major systems

Lateral line Inner ear Collectively referred to as the “acoustico-lateralis”

system

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 Systems

Lateral line – Structure Basic unit that senses motion is the neuromast Neuromast consists of cupula – jelly-like substance and

sensory hair cells

Sensory Systems

Lateral line – Structure Basic unit that sense motion is the neuromast

Sensory Systems

Lateral line – Structure Basic unit that senses motion is the neuromast

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 Systems

Lateral line – Structure Superficial neuromast Canal neuromasts

Sensory Systems

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 Systems

blind cave fish

Inner Ear Also used for mechanoreception Provides information on the orientation and movement of

a fish Critical for maintaining balance and position

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 Systems

Inner Ear – structure

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 Systems

Inner Ear – structure Otoliths

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 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

Sensory Systems

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

Behavior

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

Behavior

Dynamic displays – involve posturing Lateral displays (cichlids, anemone fishes) Frontal displays (kissing gouramis, some cichlids) Communication via sound, chemicals (alarm substance), touch,

electricity

Behavior

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

Behavior

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

% 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

BehaviorTaxon 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

% of families showing 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

Behavior - Parental Care

Behavior - Parental Care

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)

Behavior

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

Behavior

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

Behavior

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)

Behavior

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

Reproduction

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

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

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)

Reproduction

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)

Reproduction

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

Reproduction

Mating Systems Monogamy – fish mate exclusively with same individual

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

Reproduction

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 (Cyprinodontiform Rivulus); 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

Reproduction

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)

Reproduction