Why so many Teleost fish?

Why so many Teleost fish?

1. Key adaptations

   • Cycloid and ctenoid scales
   • Increased speed and mobility
     • Bony endoskeleton, matrix calcium phosphate
     • Gas filled pouch off esophagus (swim bladder, lungs)
     • Flattened scales
     • Mucus glands reduce drag
   • Homocercal tails
   • increased efficiency: gas reabsorption & secretion
     • Operculum: bony plate covering gills, attached muscles (ventilation)
   • Changes in jaw suspension
     • Progressive specialisation jaw musculature & skeletal

2. Tails and Scales

   • Tails
     • Heterocercal
       • Vertebrae into lobe
         • Upper caudal lobe larger: EPICERCAL
         • Lower caudal lobe larger: HYPOCERCAL
     • Homocercal
       • No vertebrae extension
         • Even lobes. Variety of shapes
     • Diphycercal
       • Vertebrae all the way to tip
   • Scales
     • Placoid
       • conical, tooth like
     • Ganoid
       • Diamond, ganoine + bone
     • Clycoid/Ctenoid
       • Thin, flexible, overlap

3. Circulation

   • Single cirulatory system
     • 2 Chambered heart
   • Atrium -> Ventricles -> Gills
     • O2 into blood CO2 out
     • O2 rich -> Body -> Heart
       • Capillary bed drops in pressure
   • Swimming motion aids circulation
   • Gills
     • Increased SA - Lamellae/gill filaments
       • Increased gaseous exchange - ~80%
     • Countercurrent flow

4. Swim bladder/neutral buoyancy

   • Heavier than water so need to be more buoyant
     • Sharks - heterocercal tail
     • Fish - gas filled swim bladder
   • Physostomous - pneumatic duct
     • Gulp air - increased volume
   • Physoclistous - no pneumatic duct
     • Ovale valve open - O2 moves into blood
   • Both swim bladders have:
     • Gas gland
       • lactic acid - O2 release
     • Rete mirabile
       • capillary network

5. Osmotic regulation

   • Vertebrate kidney
     • Tubular nephrons. Salts, H2O metabolites
     • 1st blood
       • Glomerulus
         • Ultrafiltrate
           • Processed
             • Glucose, amino acids & H2O
               • Remainder urine
   • Stenohaline
     • Tolerates moderate changes in salinity
   • Euryhaline
     • Tolerates large changes in salinity
   • Freshwater fish
     • Hyperosmolal
       • Lose salts (diffusion)
       • Gain water (osmosis)
       • Lots of dilute urine
     • Large Glomerulus
       • Chloride cells in gills uptake
     • Hyperosmotic regulator
   • Saltwater fish
     • Hyposmolal
       • Lose water, gain salts
     • Drink lots of sea water
     • Small glomerulus
     • Salt excretory glands
     • Hypo-osmotic regulator

6. Reproduction

   • Mass spawning e.g. cod
     • Elaborate courtship
   • Ovoparity, ovoviviparity and viviparity
   • Pelagic eggs: small, buoyant, transparent. Little yolk
   • Benthic eggs: larger, non-buoyant, adhesive & yolky
   • Some spp larval stage then metamorphosis e.g. eels

7. Migration

   • Catadromous
     • from fresh water to marine to spawn
   • Semelparity
     • Spawn and die
   • Iteroparity
     • Multiple breeding
   • Anadromous
     • Live in sea, FW to spawn