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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