Sensory Systems, Behavior, Reproduction Biology of Fishes 11.1.12

1. Sensory Systems, Behavior, ReproductionBiology of Fishes11.1.12

2. 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 • Reproduction

3. 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

4. Sensory Systems • Mechanoreception • Involves detection of movement • 2 major systems • Lateral line • Inner ear • Collectively referred to as the “acoustico-lateralis” system

5. 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

6. Sensory Systems • Lateral line– Structure • Basic unit that senses motion is the neuromast • Neuromast consists of cupula – jelly-like substance and sensory hair cells

7. Sensory Systems • Lateral line– Structure • Basic unit that sense motion is the neuromast

8. Sensory Systems • Lateral line– Structure • Basic unit that senses motion is the neuromast

9. 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

10. Sensory Systems • Lateral line– Structure • Superficial neuromast • Canal neuromasts

11. 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)

12. Sensory Systems • Inner Ear • Also used for mechanoreception • Provides information on the orientation and movement of a fish • Critical for maintaining balance and position

13. 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

14. Sensory Systems Inner Ear – structure

15. 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

16. Sensory Systems • Inner Ear – structure • Otoliths

17. 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

18. 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

19. Behavior 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

20. 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

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

22. Behavior % 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

23. Behavior % 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

24. 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

25. Behavior - Parental Care

26. Behavior • 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)

27. 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

28. 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

29. 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)

30. Reproduction 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

31. 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

32. 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

33. 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)

34. 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)

35. 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

36. Reproduction • Mating Systems • Monogamy – fish mate exclusively with same individual • N.American freshwater catfishes, butterflyfishes, some cichlids, seahorses

37. 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 (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

38. 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)