Overview of Reproduction continued 3. Physiology –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 butter hamlet

bluehead wrasse (Labridae) female & juv. male harem dominance hierarchy dominant F becomes M 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 A pprox. 400 mi. long > 1 mi. deep 5315 ft 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 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 bullhead--both sexes smallmouth bass--males 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 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

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

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 Gnathostomata 1 in Myxini 2 in Cephalaspidomorphi end

Fish Inner Ear: Fig semicircular canal lagena otolith (sagitta) utriculus otolith sacculus otolith ampullae end

Function of inner ear components: semicircular canals & ampullae -- –detect acceleration in 3D utriculus & otolith -- – gravity and orientation sacculus/sagitta & lagena/otolith -- – hearing 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

epidermis Neruomast: Fig 10.4 water fish cupula sensory cells background pulse rate increasing pulse ratedecreasing pulse rate

Lateral Line (cross section) Fig subeipdermal tissue epidermis lateral line pores cupulae lateral line canal endolymph end

Lateral Line (cross section) Fig 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