1BajaIchthyology Lecture 5 – Fall 2007 Chapter 6 - Sensory Systems• Fishes perceive external environment in five major ways- 1) Mechanoreception- 2) Vision - 3) Chemoreception- 4) Electroreception- 5) Magnetic receptionIchthyology Lecture 5 – Fall 2007 Chapter 6 - Sensory Systems1) Mechanoreception – two major systems1) Inner ear2) Lateral Line SystemMechanoreception – two major systems1) Inner ear2) Lateral Line System2Ear – Balance:Semicircular canals and utricle - 2 semi canals in lamprey; Hagfish oneCanals filled w/ fluid (endolymph) and sensory hairsOtolith (lapillus) in utricle; on sensory hairs; vert orientation w/ dorsal light reactionOtolithEar Hearing:Inner ear; Utricle, saccule and lagena - each contains otolith (lapillus, sagitta and asttericus) - lined with hairs;Ear Hearing: Most sound passes through fishDensity = 1.075 g/ml Fish; 1.026 saltwater; 1.0 freshwater Gas Bladder - many extend to ear - Clupeids3Otophysan (Ostariophysans) - Weberian ossicles - modified vertebrae that connect gas bladder to inner ear - give greatest frequency range and highest sensitivity to Otophysans of all fishes; Cichlids – new discoverySharks sensitive to low frequency and erratic pulsed sounds (injured fish)Lateral LineMechanoreception – Lateral Line System - detect vibrations in water; sound waves displace neuromasts (free standing, in skin or dermal bone (cephalic pores); found in all fish;2) Vision - Eyes similar to vertebrates;Cornea (thinner - light does not have to bend); iris and pupil (elasmobranchscan adjust shape of iris/pupil; teleosts cannot); Lens (spherical) – move lens to focus; retina (rods and cones are sensory cells); sclera (outer strong layer); choroid (vascularized between retina and sclera);4Rods - sensitive to low light levels; crepuscular and deep sea species = many rods Cones - bright light; some Elasmos and most teleosts; Four types of cones w/ different color reception including ultraviolet and polarized lightCone ArrangementsFreshwaterMarine - littoralMarine - DeepWeird eyes - some deep sea = elongate tubular eyes; mud skippers - aerial vision (strong curved cornea and flattened lens on retractable stalks); Four eyed fish (Anableps) = simultaneous vision above and below water (two pupils and retina w/ dorsal and ventral sections) Chemoreception involves both smell (olfaction) and taste (gustation) - distinction clear in terrestrial but not so distinct in water Nasal (olfactory) sacs w/ one or two nares in jawed fish; Most dead-end so they do not breath through; folded olfactory epithelium - odors bind to receptors; better sense of smell = more folds;Agnathans = single naris and median olfactory sac; Hagfish connected to gills; Chimeras and lungfish also connectedSmell used for homing (Salmon find streams by odor not vision), locate mates (pheromones; deep sea angler fish);Taste - internal and external taste buds; some catfish have all over body3) Chemoreception53) Chemoreception• Taste -internal and external taste buds; some catfish have all over body 4) Electrorecption many fish detect electricity• Sharks, catfish detect prey by homing in on weak electric fields or slight muscle activity;• Mormyrids and gymnotidsdetect electric fields generated by electric organs;• Two types of electroreceptors• 1) Ampullary receptors - lie at base of canal filled w/ conductive gell; ampullae of Lorenzini in Sharks; • Sensitive to low frequency AC/DC - do not produce; Can use magnetic fields for navigation4) Electroreception•Two types of electroreceptors• 2) Tuberous receptors - respond to high frequency AC; most sensitive to electric organ discharges; Fish that generate have both.Electric communication• Electrical Communication = Main use of electricity;• Amplitude, frequency, pulse length vary;• Species and sex recognition - social attacks, submission, courtship, dominance hierarchies; • Can also interfere with other outputs –Jamming• Can also have Jamming Avoidance Response (e.g. prevent jamming by changing discharge)6Mauthner cells and startle response - extremely quick movement; rapid conduction of nerve pulses along specialized nerve cells (Mauthner cells) = large diameter and myelin sheath = fastest conduction in verts; along brain stem; crosses over brain and bypasses and descends along spinal curve (receives input from right goes to left muscles); If one receives input it will inhibit the other; tail flick response.5) Magnetic Reception• Few highly migratory ray-finned fishes can detect earth-strength magnetic fields• Specific mechanisms of magnetic receptionare unknown• Magnetite in heads of some tunas (e.g. yellowfintuna) and in nares of some anadromous salmon (subfamily Salmoninae). • Magnetic perception thought to help fish locate long distance migration routes for feeding and