Shark Lecture

Shark Lecture - Ratfishes Sharks Skates and Rays Class...

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Ratfishes, Sharks, Skates, and Rays Class Chondrichthyes: Subclasses Holocephali and Elasmobranchii Chondrichthyes ± Held in low regard ± Considered viscous, inedible, and primitive ± Not generally true ± Group is not primitive ± As specialized as teleosts, but in their own way Chondrichthyes II ± Less diverse than teleosts ± Most spp are predators on large invertebrates and fishes ± Extreme diversity in ways of making a living is lacking ± As predators their success is undisputed ± Success due to a combination of characters ± Buoyancy ± Respiration ± External Covering ± Feeding ± Movement ± Sensory Systems ± Osmoregulation ± Reproduction
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Buoyancy I ± Problem: How to stay off the bottom without burning too much energy ± Ideal is neutral buoyancy ± Apparently ideal not available to Chondrichthyes, limited their diversity ± Many spp never left the bottom ± Skates, Rays, and many Sharks are benthic or bottom oriented Buoyancy II ± Characteristics that reduce or counteract relative density (weight in water) ± Cartilaginous skeleton ± Oily livers ± Hydrodynamic lifts Buoyancy III Tail Pectoral fin Buoyant liver Pectoral fin lift Heterocercal tail depression Cartilagenous skeleton Respiration ± 3 basic methods (not exclusive) ± Buccal and opercular pumping (Fig 3.5) ± Ram ventilation ± Spiracle preceding first gill slit Used to draw water into oral cavity and over gills, esp in benthic forms Lost is some spp, esp pelagic sharks that “ram” water over gills by constant swimming In other pelagic spp, it is important in supplying oxygen to eyes External Covering ± Placoid scales in some form ± In skates and rays, typically present as rows of denticles on back, sometimes modified into spines (stingrays) ± Shark skin sandpaper: smooth in one direction only ± Overlapping scales increase hydrodynamic efficiency Modified placoid scales: denticles and sting
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Feeding ± Each spp of Chondrichthyes has distinctive teeth that reflect the way it makes a living ± Teeth are modified placoid scales ± Teeth continuously shed and replaced (est 30,000 / lifetime) ± Three basic shapes: triangular, thin-pointed, or pavement-like Feeding II ± Large triangular blade-like teeth in predators of large fish and marine mammals for cutting and tearing ± May exert pressure of 2800kg/cm 2 (40,000 psi) ± Sharks that swallow whole prey have long, thin, pointed teeth for grasping ± Skates and rays have pavement-like teeth for crushing hard-shelled inverts Feeding III ± Most sharks are able to ingest surprisingly large prey because of loose jaw suspension (hyostylic) ± Initial digestion in large stomach ± Spiral valve intestine highly efficient means of increasing gut surface area without increasing length ± White shark (McCosker 1987) stomach 7.4 o C warmer than ambient water: rapid digestion Tiger shark Largetooth sawfish --Pristis microdon
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Mako shark Cownose stingray -- Rhinoptera bonasus
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This note was uploaded on 09/13/2010 for the course OCS 4012 taught by Professor Baltz,d during the Spring '08 term at LSU.

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Shark Lecture - Ratfishes Sharks Skates and Rays Class...

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