Transcript Ichthyology Fall 2000

Overview of Reproduction continued
3. Physiology
butter hamlet
– sex chromosomes:
• XY = M; XX = F (most)
• ZZ = M and ZW = F (Poeciliidae & Tilapia spp)
• some fishes have 3 or more sex chromosomes
– sex not under complete genetic control
• hermaphrodites--both sexes (many in Serranidae)
– usu. one sex at a time
– exception hamlet (serranid)
• sex changes--bluehead wrasse
end
bluehead wrasse (Labridae)
male
• harem
• dominance hierarchy
• dominant F becomes M
female & juv.
end
Overview of Reproduction continued
3. Physiology continued
– parthenogenesis -- egg develops w/o fertilization
• Ex: Amazon molly
– all female
– produce genetic clones
• Ex: gynogenesis in Phoxinus (Cyprinidae)
– all female
– gynogenesis--sperm required, DNA from male not
incorporated in embryo
end
Reproductive Modes in Fishes:
• Oviparous -- egg layers; most fishes
– internal or external fertilization
• Ovoviviparous
–
–
–
–
–
internal fertilization
eggs hatch internally
live birth
yolk only nutrition
EX: Lake Baikal sculpins
• marine rockfishes
• some sharks
end
Lake Baikal
Approx. 400 mi. long
5315 ft
> 1 mi. deep
end
Reproductive Modes in Fishes: continued
• Viviparous--live birth
– nutrition provided directly by mother
– EX: embryonic cannibalism -- a few sharks
• fins against uterine wall -- surf perches
• placenta-like structures--pericardial tissues in
Poeciliidae
end
nurse shark embryos
end
lemon shark pup
yolk sac and stalk function like placenta and umbilical cord
end
Reproductive Strategies:
Energy Investment
egg size: number vs. survivability
carp > 2,000,000
salmon 1500-2000
parental investment: energy vs. surviv.
nest building
parental care
mouth brooders--cichlids; ariids
end
Parental care: pouches (seahorses, pipefishes)
end
female
male
end
Parental care: guarding
smallmouth bass--males
bullhead--both sexes
end
end
Sensory Perception
• Most fishes have familiar senses:
–
–
–
–
–
sight
hearing
smell
taste
touch
• Senses generally similar to those of other
verts.
end
Overview of Sensory Differences
1. Chemoreception
– taste & smell; distinction blurred in water
2. Acustico-lateralis System
– sensing of vibrations; hearing & lateral line
3. Electroreception
– sensing electromagnetism from earth & orgs.
4. Pheromones
– chemical messages from other fish
end
1. Chemoreception details
• Olfaction & taste --sense chemicals
• Differences:
– location of receptors:
• olfaction -- special sensory pits
• taste -- surface of mouth, barbels
– sensitivity
• olfaction -- high
• taste -- lower
end
Olfaction details:
• Sense food, geog. location, pheromones
• structure -- olfactory pit
– incurrent & excurrent openings (nares) divided by
flap of skin
– olfactory rosette -- sensory structure; large surface
area
• water movement driven by:
– cilia
– muscular movement of branchial pump
– swimming
end
Olfaction details continued:
• Sensitivity varies--high in migratory spp.
• Odors perceived when dissolved chem. makes
contact with olfactory rosette
• anguilid eels detect some chems. in conc. as low
as 1 x 10-13 M !
– M = # moles per liter
• salmon detect amino acids from the skin of
juveniles
• sea lampreys detect bile acids secreted by larvae
• directional in nurse, hammerhead sharks
end
Taste details-- short-range chemoreception
• detects food, noxious substances
• sensory cells in mouth and on external
surfaces, skin, barbels, fins
• particularly sensitive to amino acids, small
peptides, nucleotides, organic acids
end
end
2. Acoustico-lateralis system
• Detects sound, vibration and water
displacement
• Functions in orientation & balance
• Organs:
– inner ear (no external opening, no middle ear,
no ear drum)
– lateral line system
end
Hearing details:
• sound travels farther & 4.8 x faster in water
• sound waves cause body of fish to vibrate
sensory structure of ear
sensory hairs
otolith
end
Hearing details continued:
• inertia of otoliths resist vibration of fish
• sensory hairs bend, initiating impulse
• nerves conduct impulse to auditory region
of brain
end
Hearing details continued:
• certain sounds cause insufficient vibration
– weak sounds
– high frequency
– distant sounds
• enhancements for sound detection
– swim bladder close to ear
– swim bladder extensions (clupeids, mormyrids)
– Weberian apparatus--ossicles (ostariophysans)
end
Gnathostomata
Structure of Inner Ear:
• 3 semicircular canals--fluid-filled tubes w
sensory cells (hair-like projections)
• 3 ampullae--fluid filled sacs w sensory cells
• 3 sensory sacs containing otoliths
– otoliths--calcareous bones; approx. 3x as dense as
fish
• 1 in Myxini
• 2 in Cephalaspidomorphi
end
Fish Inner Ear: Fig. 10.2
semicircular canal
ampullae
lagena
otolith
utriculus
sacculus
otolith
otolith (sagitta)
end
Function of inner ear components:
• semicircular canals & ampullae -– detect acceleration in 3D
• utriculus & otolith -– gravity and orientation
• sacculus/sagitta & lagena/otolith -– hearing
end
end
Lateral line
• detects water movement
– low frequency vibrations
– specialized for fixed objects and
– other organisms
• Neuromasts -- fundamental sensory structure
– single or part of lateral line system
Neruomast: Fig 10.4
cupula
water
decreasing pulse rate
increasing pulse rate
epidermis
fish
sensory cells
background pulse rate
Lateral Line (cross section) Fig. 10.5
lateral line pores
cupulae
epidermis
lateral line canal
endolymph
end
Lateral Line (cross section) Fig. 10.5
vibrations
nerve impulse to brain
Lateral line details:
• often well-developed on head
• system poorly developed in lampreys and
hagfishes--neuromasts only
• often no lateral line in inactive fishes
• well-developed in blind cave fishes
• functions like a sort of sonar
– exploration -- higher speed “swim-by”
end