Lecture 4 Chondrichthyes I Shark Diversity. Inaugural Day Ichthyology Lecture

Transcription

1 Lecture 4 Chondrichthyes I Shark Diversity Inaugural Day Ichthyology Lecture

2 Lecture 4 Chondrichthyes I Shark Diversity 2

3 SHARK

4 Cartilaginous fishes: Sharks, skates, rays, chimaeras (ratfishes) Date to Silurian 450 MYA; major radiations in the Paleozoic and Mesozoic (including the branch that includes modern sharks, skates and rays; talk more in a few weeks) Today: overview of the diversity of extant Chondrichthyians, major traits and adaptations especially of the elasmobranchs 4

5 Ages of Rock by Ray Troll 5

6 Jawed vertebrates Classes: Placodermi {extinct} Chondrichthyes Superclass Gnathostomata Cartilaginous fishes Acanthodii {extinct} Sarcopterygii Lobe-finned fishes, tetrapods Actinopterygii Ray-finned fishes 6

7 Living chondrichthyans are in 2 major groups: Class Chondrichthyes (cartilaginous fishes) Subclass Elasmobranchii (sharklike fishes) Infraclass Euselachii (modern sharks and rays) Subclass Holocephali Superorder Holocephalimorpha (chimaeras) 7

8 Living chondrichthyans are in 2 major groups: Class Chondrichthyes (cartilaginous fishes) Subclass Elasmobranchii (sharklike fishes) Infraclass Euselachii (modern sharks and rays) 9 orders of sharks - > 403 species 4 order of skates and rays - > 534 species Plus many undescribed spp; rays most diverse Subclass Holocephali Superorder Holocephalimorpha (chimaeras) 1 order - 33 species 970 EXTANT species 8

9 Modern elasmobranchs generally large >1 m with a calcified but seldom ossified skeleton. They differ from bony fishes in that: 1) Skull lacks sutures 2) teeth are NOT fused to the jaws but are instead embedded in the connective tissue of the jaws. 3) Teeth, which have the same embryonic origin as and may be derived from placoid scales are replaced serially; such replacement is less common in osteichthyans. 4) The biting edge of the upper jaw is formed by the palatoquadrate cartilage, rather than by the maxillary or premaxillary bones. The palatoquadrate is free from the brain case, creating a protrusible upper jaw during feeding (amphistylic condition). 5) The mouth is subterminal (= ventral). Nasal openings are ventral and incompletely divided by a flap into incurrent and excurrent portions; bony fishes generally have completely separated, dorsallypositioned nasal openings. 6) Fin rays in elasmobranchs are soft, horny, unsegmented ceratotrichia. (from Helfman et al. ) 9

10 Typically sharks, skates, and rays usually have 5, sometimes 6 or 7 external gill slits. The first gill slit of elasmobranchs is often modified as a spiracle, supported by the hyoid arch and first functional gill arch. Elasmobranchs lack lungs and gas bladders, but possess large, buoyant livers and spiral valve intestines. Internal fertilization is universal to the group; males possess pelvic-fin derived intromittent organs (myxopterygia or claspers) and females either lay eggs or nourish embryos internally for several months before giving birth. Chloride ions, and metabolic waste products in the form of urea and trimethylamine oxide (TMAO, an ammonia derivative), are concentrated in the blood and serve in osmotic regulation. A single cloaca serves as an anal and urogenital opening. (from Helfman et al. Ch 12) 10

11 Class Chondrichthyes (cartilaginous fishes) Subclass Elasmobranchii (sharklike fishes) Infraclass Euselachii (sharks and rays and related fossils) Division Neoselachii (includes modern sharks and rays) Subdivision Selachii (sharks 9 Orders) have (1) gill openings on the sides of the body; (2) the anterior edge of the pectoral fin not attached to the side of the head; (3) anal fin present in galeomorphi but absent in squalomorphi (except for the 5 species of hexanchiformes); and (4) have small lateral spiracles compared with large dorsal spiracles in rays. Subdivision Batoidea (skates and rays 4 Orders) (1) gill openings ventral; (2) anterior edge of enlarged pectoral fin attached to the side of the head; (3) anal fin absent; (4) intake of water for breathing chiefly through an enlarged dorsal spiracle (except in water column species). 11

12 Phylogenetic Relationships among living chondrichthyans 12

13 > 403 spp in 9 orders Sharks Echinorhiniformes Bramble sharks 1 genus, 2 spp Anal Fin Absent Hexanchiformes Six-gill sharks 2 families, 5 spp Squalomorphi Squaliformes Dogfish sharks 6 families, > 97 spp Pristiophoriformes Saw sharks 1 family, 9 spp > 75% of species in 2 orders Selachii Squatiniformes Angel sharks 1 family, 15 spp Heterodontiformes Bullhead sharks 1 family, 9 spp Galeomorphi Orectolobiformes Carpet sharks 7 families, 32 spp Anal Fin Present Carcharhiniformes Ground sharks 8 families, >224 spp Lamniformes Mackerel sharks 7 families, 15 spp

14 Class Chondrichthyes (cartilaginous fishes) Subclass Elasmobranchii (sharklike fishes) Infraclass Euselachii (sharks and rays) Division Neoselachii Subdivision Selachii (sharks) Superorder Galeomorphi (Anal Fin Present) Order Heterodontiformes (8 species, marine): Heterodontidae (bullhead, horn sharks) Order Orectolobiformes (32 species, marine): Parascyllidae (collared carpet sharks), Brachaeluridae (blind sharks), Orectolobidae (wobbegongs), Hemiscylliidae (bamboo sharks), Stegostomatidae (zebra sharks), Ginglymostomatidae (nurse sharks), Rhincodontidae (whale sharks) Order Lamniformes (15 species, marine): Odontaspididae (sand tiger sharks), Mitsukurinidae (goblin sharks), Pseudocarchariidae (crocodile sharks), Megachasmidae (megamouth sharks), Alopiidae (thresher sharks), Cetorhinidae (basking sharks), Lamnidae (mackerel sharks) Order Carcharhiniformes (224 species, mostly marine): Scyliorhinidae (cat sharks), Proscylliidae (finback cat sharks), Pseudotriakidae (false cat sharks), Leptochariidae (barbeled hound sharks), Triakidae (houndsharks), Hemigaleidae (weasel sharks), Carcharhinidae (requiem sharks), Sphyrnidae (hammerhead sharks) Superorder Squalomorphi (Anal Fin Absent-except Hexanchiformes) Order Hexanchiformes (5 species, marine): Chlamydoselachidae (frill sharks), Hexanchidae (cow sharks) Order Echinorhiniformes (2 species, marine): Echinorhinidae (bramble sharks) Order Squaliformes (97 species, marine): Squalidae (dogfish sharks), Centrophoridae (gulper sharks), Etmopteridae (lantern sharks), Somniosidae (sleeper sharks), Oxynotidae (rough sharks), Dalatiidae (kitefin sharks) Order Squatiniformes (15 species, marine): Squatinidae (angel sharks) Order Pristiophoriformes (5 species, marine): Pristiophoridae (saw sharks) 14

15 Florida Museum of Natural History

16 Orectolobiformes, carpet sharks, 32 species, mouth well in front of eyes, but varied ambush predators on octopi, invertebrates and fishes

17 Orectolobis ornatus Banded wobbegong Class: Carlilagenous Fishes (Chondrichthyes) Order: Carpetsharks (Orectolobiformes) Family: Wobbegongs (Orectolobidae) Genus: Orectolobus (Orectolobus) Ginglymostoma cirratum Nurse Shark Order - Orectolobiformes Family - Ginglymostomatidae Genus - Ginglymostoma Species - cirratum Orectolobiformes carpet sharks, 7 families, 32spp

18 The whale shark was first described and named by Andrew Smith in 1828, based on a specimen harpooned in Table Bay, South Africa. Historically, there have been many synonyms (alternative scientific names) for family, genus and species names. The first scientific printing of the genus name appeared as Rincodon, despite Smith's desired name of Rhineodon. However, in 1984 the International Commission on Zoological Nomenclature suppressed previous generic variations in favor of genus name Rhincodon, and the family name Rhincodontidae. Rhincodon typus Whale Shark Class: Carlilagenous Fishes (Chondrichthyes) Order: Carpetsharks (Orectolobiformes) Family: Rhincodontidae Genus: Rhincodon typus Orectolobiformes carpet sharks, 7 families, 32spp

19 Rhincodon typus Whale Shark Class: Carlilagenous Fishes (Chondrichthyes) Order: Carpetsharks (Orectolobiformes) Family: Rhincodontidae Genus: Rhincodon typus Orectolobiformes carpet sharks, 7 families, 32spp

20 ...as of Nelson 2006, in family Sphyrinidae, to paraphrase Archie Carr..any damned fool knows a hammerhead.. TIGER SHARK Order - Carcharhiniformes BLUE Family SHARK - Carcharhinidae Order Genus - Carcharhiniformes - Galeocerdo cuvier Family - Carcharhinidae Genus - Prionace glauca GREAT HAMMERHEAD Order - Carcharhiniformes Family - Sphyrnidae Genus - Sphyrna mokarran Carchariniformes ground or requiem sharks lack gill rakers--largest group, 8 families, 49 genera, > 224 spp mouth extends behind eye

21 Order: Lamniformes Family: Order MEGAMOUTH - Odontaspididae Lamniformes SHARK Genus: Family Order Carcharias - Lamnidae - Lamniformes taurus Genus Family - Carcharodon - Megachasmidae carcharias Order: Lamniformes Genus - Megachasma pelagios Family: Lamnidae Genus: Lamna ditropis Lamniformes mackerel sharks 7 families, 10 genera, 15spp. pelagic

22 Although the Greenland shark is poisonous if eaten fresh, it is edible when the meat has been dried. The flesh of the shark contains high concentrations of urea and trimethylamine oxide TMAO, which is said to be intoxicating, inducing an alcoholic affect. For this reason, natives of Greenland are known to call someone who is drunk "sharksick." SPINY DOGFISH Order: Squaliformes Family: Squalidae Genus: Squalus acanthias GREENLAND SHARK Order: Squaliformes Family: Somniosidae Genus: Somniosus microcephalus PRICKLY DOGFISH Order: Squaliformes Family: Oxynotidae Genus: Oxynotus bruniensis 6m Greenland Shark Squaliformes, dogfish sharks 6 families, 24 genera, >97spp no anal fin

23 FRILL SHARK Order: Hexanchiformes Family: Chlamydoselachidae Genus: Chlamydoselachus anguineus Hexanchiformes, six-gill sharks 2 families,4 genera 5 spp

24 Batoidea > 534 spp in 4 Orders dae Rajidae Skates, 238 spp Rajiformes Rajidae, Rhinobatidae, 2 other families w/5 spp 285 spp Pristiformes 1 family, 7 spp Pristidae Sawfishes, 7 spp Torpedinidae, Narcinidae Electric rays, 59 spp Torpediniformes 2 families, 59 spp Myliobatidae, Dasyatidae, 8 others Stingrays,183 spp dae Myliobatiformes 10 families, 183 spp Rhinobatidae Guitarfishes, 42 spp

25 Subdivision Batoidea (skates and rays) Order Torpediniformes (59 species, marine): Torpedinidae (torpedo electric rays), Narcinidae (numbfishes) Order Pristiformes (7 species, marine and freshwater): Pristidae (sawfishes) Order Rajiformes (285 species, marine): Rhinidae (bowmouth guitarfishes), Rhynchobatidae (wedgefishes), Rhinobatidae (guitarfishes), Rajidae (skates) Order Myliobatiformes (183 species, marine and freshwater): Platyrhinidae (thornbacks), Zanobatidae (panrays), Hexatrygonidae (sixgill stingrays), Plesiobatidae (deepwater stingrays), Urolophidae (round stingrays), Urotrygonidae (American round stingrays), Dasyatidae (whiptail stingrays), Potamotrygonidae (river stingrays), Gymnuridae (butterfly rays), Myliobatidae (eagle rays) 25

26 Rajiformes, skates and rays anterior edge of enlarged pectoral fin attached to side of head

27 WHITESPOTTED GUITARFISH Order - Rajiformes Family - Rhynchobatidae Genus - Rhybchobatus djiddensis Rhynchobatidae wedgefishes 1 genus 4 spp RAJIFORMES. wedgefishes can be large, up to 3m and > 200kg

28 Sawfishes Pristiformes 1 Family, 2 genera 7 spp. up to 7m! *note pectoral fins

29 LESSER ELECTRIC RAY Order - Torpediniformes Family - Narcinidae Genus - Narcine brasiliensis Electric Rays 2 families > 59spp Numbfishes

30 SPOTTED EAGLE RAY Order: Myliobatiformes Family: Myliobatidae Genus: Aetobatus narinari Myliobatiformes stingrays 10 families >200 spp 1 to 2 caudal spines, mostly marine, freshwater exceptions

31 Giant Freshwater Stingray, Himantura chaeophraya up to 2m disk width, 600kg!! rivers in Thailand,Borneo,New 600 Guinea, kg Australia

32 MANTA Order: Myliobatiformes Family: Mobulidae Genus: Manta birostris Devil rays only living vertebrate with three pairs of functional limbs cephalic pair -anterior subdivision of pectorals. Uses cephalic fins to guide plankton, fishes, crustaceans into terminal mouth.

33 River Stingrays- Potamotrygonidae, 20 spp. Restricted to low salinity, have lost the ability to survive in more than 15 ppt salinity 33

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36 Subclass Holocephali! Superorder Holocephalimorpha (6 extinct orders and modern chimaeras (also known as ratfishes and rabbitfishes), from Late Devonian to present (much reduced diversity after Permian).!!! Order Chimaeriformes (modern chimaeras) (33 species, marine): Callorhinchidae (plownose chimaeras), Rhinochimaeridae (longnose chimaeras), Chimaeridae (shortnose chimaeras or ratfishes) 36

37 Most characters that define elasombranchs also describe Holocephalans-indicating a common but unknown ancestor. What they share: 1) cartilaginous skeleton, 2) sutureless skull, 3)ceratotrichial fins, 4) spiral valve intestine, 5) lack lungs and gas bladders, 6) use oil-filled liver for buoyancy, 6) direct development without a larval stage. Differences include: 1) upper jaws immovable attached to the braincase (holostylic condition-hence whole head for Holocephali, 2) teeth are continually growing, crushing plates instead of serially replaced dentition, 3) Chimaeras have 3 pairs of tooth plates-two pair of vomerine and palatine plate pairs in the upper jaws and a large mandibular pair on the bottom (hence rabbitfish)-anterior plates are blade-like and posterior are flattened for crushing hard prey items, 4) 4 internal gill openings covered by gill flap, 5) lack spiracular gill opening, 6) No cloaca, separate anal and urogenital openings, 7) males with shark-like pelvic claspers, extensions of the pelvic fins and pre-pelvic stout spines called tenaculae used to anchor the female during copulation, 8) males also have a frontal tenaculum on the head used to grasp the females pectoral fin during copulation, 9) generally lack scales-except for denticles on midline of back and claspers of male. They are oviparous-laying few 10cm eggs in horny shells. First dorsal spine is poison laden, erectable, not fixed (Helfman et al.) 37

38 CHIMAEROID FISHES OF NEW CALEDONIA WITH DESCRIPTION OF A NEW SPECIES OF HYDROLAGUS (CHONDRICHTHYES, HOLOCEPHALI) by Dominique A. DIDIER (1) & Bernard SÉRET (2) ABSTRACT. - Three species of chimaeroid fishes are reported from deep waters around New Caledonia: Chimaera phantasma, Rhinochimaera pacifica and Hydrolagus trolli n. sp., which is described from 23 specimens collected from New Caledonia and New Zealand at depths of m. The new species is distinguished from all other members of the genus by its blue-gray coloration, distinctly pointed snout, first dorsal fin concave along its posterior edge with a pale margin, preopercular and oral lateral-line canals usually sharing a common branch, males with a robust frontal tenaculum with the distal bulb upturned at its distal edge, denticles extending onto the dorsal surface and bifid pelvic claspers with the distal 1/3 divided and pale colored, fleshy distal lobes. Figure 6. - Secondary sexual characteristics of adult males of Hydolagus trolli sp. n. A: Frontal tenaculum in dorsal and lateral view. B: Prepelvic tenaculum in dorsal view showing denticles along medial edge and fold of skin on lateral surface. C: Pelvic clasper in ventral (left) and dorsal (right) views. Arrow indicates dashed line marking the location of the clasper groove. Hydrolagus trolli 38 Didier and Seret, 2002, Cybium 26(3)

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40 Subclass Holocephali Superorder Holocephalimorpha! Order Chimaeriformes chimaeras/ratfishes, 3 families, ca. 33 spp chimerical \ky-mer-ih-kuhl; -MIR-; kih-\, adjective: 1. Merely imaginary; produced by or as if by a wildly fanciful imagination; fantastic; improbable or unrealistic. Chimerical is ultimately derived from Greek khimaira, "she-goat" or "chimera," which in Greek mythology was a monster having the head of a lion, the body of a goat, and the tail of a dragon.

41 Ratfish Rule

42 Chondrichthyan characteristics include: endoskeleton calcification pelvic claspers Key synapomorphies placoid scales teeth usually not fused to jaws, replaced serially fin rays soft, unsegmented biting edge of upper jaw formed by palatoquadrate swimbladder and lung absent usually high concentrations of urea and trimethylamine oxide in blood (osmoregualtion) intestinal spiral valve

43 Placoid scales

44 REPLACEMENT DENTITON Tiger Shark Teeth In bony fishes teeth attached directly to bone, IN sharks teeth embedded in connective tissue-and only on jaw margins, not other structures in mouth. Basically enlarged scales embryologically Replacement occurs regardless of use, nonfunctional teeth in interior rows grow and move forward, displacing or replacing functional teeth. Turnover rates for sharks in captivity range from 2 days to 8 or 10 to 28, giving an estimate of the order of 30,000 IN A LIFETIME

45 Rays and Skates usually with crushing pavement teeth Barn-door skate Raja laevis Mitchill

46 General Chondrichthyan Traits 1. Large size 2. Marine

47 Freshwater exceptions

48 3. Mobile! Local nearshore 100 s km bull, nurse, bonnethead Coastal 1000 s kms along continental shelves, sandbar, blacktip dusky Oceanic -- 10s of 1000 s km migrate across ocean basins whale, white, blue Oil-based buoyancy (livers up to 90% oil) allows for large vertical migrationswithout adjusting air bladders-sharks essentially neutrally buoyant. Reduced skeletal density -55% density of bone.

49 4. Predatory Top of Food Webs carnivores or scavengers

50 Sawfishes and saw sharks - Pristid sawfishes (Rajiforms), pristophorid sawsharks (Pristophoriformes) bladelike snouts with lateral teeth slash to stun prey

51 Cookie cutter sharks, Isistius brasiliensis ectoparasitic elasmobranch-ventral surface covered with photophores, shark bites from above attacking prey attracted to the light, spinning and removing a plug of flesh!

52 Filter Feeders

53 ICHTHYILLITERACY OF THE DAY

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55 Claspers, Male Sand-Tiger Shark (Lamniformes) Myxopterygia 5. Internal fertilization Whitetip reef sharks; from Pratt and Carrier 2001

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57 6. Direct development and precocial young 7. Low fecundity, late maturation

58 A summary of embryonic development and nutrition in chondrichthyans. From Nelson (2006), after Musick and Ellis (2005). I All nutrition from yolk sac A. Yolk sac viviparity (= lecithotrophic viviparity, ovoviparity): all living orders except heterodontiforms, lamniforms, and rajiforms B. Yolk sac oviparity (= lecithotrophic oviparity): all living holocephalans, all Heterodontiformes, some Orectolobiformes, some Carcharhiniformes and all Rajiformes II Some nutrition from mother (= matrotrophy) A. Nutrition from uterine secretions (= histotrophy): many squaliforms and carchariniforms, and all myliobatiforms B. Nutrition from eating unfertilized eggs (= oophagy): all lamniforms and some carchariniforms (includes embryophagy of Carcharias taurus) and pseudotriakids 58

59 MODES OF EMBRYONIC NUTRITION The alternative condition is egg-laying (oviparity), with the embryo deriving ALL nutrition from its large yolk reserves. About 40% of living elasmobranchs are oviparous, including bullhead sharks (Heterodontiformes), many nurse sharks (Orectolobiformes), as well as all skates (Rajiformes). Clutch sizes among oviparous sharks and batoids both average about 60 eggs per year (Musick and Ellis 2005). Shark and skate egg cases large (2-4cm) horny keratonoid shell protecting a single embryo, attached to seaweed or other structure-the embryo develops weeks up to 15 months. 59

60 About 70% of living sharks and all ray species bear live young In about half of live-bearing species, the developing embryo is retained in the uterus and nourished with yolk provided by a yolk sac that is attached directly to the digestive system of the embryo (termed variously yolksac-, lecithotrophic-, or aplacental-viviparity, and also ovoviviparity)-many species including frill, cow, dogfish, angel, some carcharhinids and orectolobids (tiger and nurse), whale shark (up to 300 embryos-most fecund shark known), sawfishes and torpedo rays. Some ovoviviparous sharks have evolved an additional form of nourishment- oophagy- in which the young feed on ovulated eggs after exhausting yolk reserves (threshers, whites, makos, sand tigers. Sand tigers carry this further the first embryo to consume its yolk, eats its siblings (embryophagy) before assuming an oophagus existence. At birth, litter size in sand tigers is 2 large (1m) young, one in each uterus. 60

61 Extra Credit Tiny Desk Lecture 61

62 The most complex development pattern is placental viviparity, in which the spent yolk sac attaches to the uterine wall to form a yolk-sac placenta. The stalk of the yolk sac forms an umbilical cord, attached to the embryo between the pectoral fins, transporting nutrients and oxygen to the embryo and metabolic wastes to the mother. In some sharks such as hammerheads and sharpnose, the cord diversifies and develops outgrowths (appendicula) that serve as sites for exchange of materials, including uptake of nutrients, from the uterine milk. In myliobatoid stingrays and manta rays, nourishment is obtained solely from uterine milk without a placental connection-termed uterine viviparity. 62

63 (A) 10, Mammals Brain weight (g) Elasmobranchs Birds 1 Fish , ,000 Body weight (kg) 63 Helfman et al.

64 (B) 100 Sharks Log 10 brain mass (g) 10 Teleosts Figure Brain size in sharks. (A) Sharks have relatively large brains for their body size, overlapping in this respect with birds and mammals as much as with bony fishes. (B) Among pelagic, predatory fishes, many sharks have relatively large brains for their body mass. (A) from Springer and Gold (1989), based on Northcutt (1977) and Moss (1984), used with permission; (B) after Lisney and Collin (2006) Log 10 body mass (kg) 64 Helfman et al.

65 10 SEC 8. Large brain, acute nonvisual senses 30 SEC 2 MIN

66 Carcharhinus plumbeus Sphyrna lewini Sharks attracted to energized electrode 66

67 Ampullae of Lorenzini (after Stephano Lorenzini)

68 . Many biological activities have as an integral component the generation of weak electricity. Most notable are muscular contraction, such as heart function and breathing, nerve conduction, and the voltage created by ionic differences between protoplasm and water. A resting flatfish (Pleuronectiformes) creates a low frequency d.c. (direct current) bioelectric field with a strength of more than 0.01 uv/cm (1 hundredth of a microvolt) measured 25 cm away. Ampullae of Lorenzini Experiments have shown that predatory sharks use weak electrical cues, and ignore strong olfactory cues, to home in on prey. The electrical sensitivity of large sharks is truly amazing. Human sensitivity is on the order of 0.1 volt. Sharks have demonstrated detection thresholds of 1 x 10-9 V/cm or 1 billionth of a volt, approximately 10 times more sensitive than the 0.01 mv output from prey. Such sensitivity would be sufficient to detect the electrical output of a standard D-cell flashlight battery several km away (assuming no background geomagnetic interference), or the bioelectric output of a human 1-2 m away. (from Helfman et al.) Sharks have an additional channel for sensory input that is anatomically and developmentally related to distant-touch and hearing, namely electroreception (Collin and Whitehead 2004). Input for electroreception begins at numerous small pores spaced precisely on the shark's head, snout, and mouth. The pores lead to conductive, jelly-filled canals which terminate in ampullary receptor cells termed ampullae of Lorenzini. The receptor cells, which are anatomically similar to hair cells of the lateral line, fire in response to weak electric fields, sending through afferent fibers via the lateral line nerve to regions in both the mesencephalon and telencephalon of the brain. The function of the ampullae, which are an obvious external feature on most sharks, remained a substantial mystery prior to the discovery of electroreceptive capabilities in sharks. 68

69 LAB EXPERIMENTS ON ELECTRICAL SENSITIVITY Kalmijn 1966: skates react to currents as low as 0.01 microvolts (uv)/cm = V we react to 0.1 V we are 1 million times less sensitive Fish produce a D.C. electric field of 0.05 uv detectable 25 cm away = 5X a skate s sensitivity

70 flatfish in sediment attracted flatfish in sediment inside agar block attracted Meat in sediment inside agar block attracted to odor flatfish in sediment inside agar block, plastic (electrical) shield NO ATTRACTION Two Electrodes in sediment attracted

71 FIELD EXPERIMENTS Bites at activated pole = 40 at control pole = 8 at odor source = 2 Feeding attacks by blue shark Prionace glacuca on electrically simulated prey; os = odor source d1 = electrodes passing a current of 8 microamps d2 = control electrode Kalmijn 1982 Science 5 nv = cm, ultimately 1x10-9 or V/cm! (you wanna talk about nannotechnology?)

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