Respiration

Jawless Fishes  Gills - pore-like openings  7 pairs of gill pouches in lamprey  5-15 pairs of gill pouches in hagfish, but varying numbers of openings (as few as one/side)

Hagfish gills  Gill pouches connect directly to pharynx  Two gills in each pouch  May or may not open directly to outside (depending on species)  May play role in digestion/nutrient absorption

Lampreys  Problems with respiration during feeding - no water via pharynx  Developed separate canal to carry respiratory water - from pore on head to gill pouches

Lamprey gills  Two gills per pouch  Each pouch has separate exit pore to outside

Gills in Chondricthyes and Osteichthyes  Gill filaments attached to posterior sides of bony or cartilaginous gill arches  Gill rakers located on anterior sides of arches

Class Chondrichthyes  Gills (pairs of them) located in separate chambers leading from pharynx  Chambers separated by septa (tissues) gills are septate  Each has separate gill slit to outside

Skates and rays  Skates and rays have ventral gill slits

Skates and rays  Spiracle behind each eye - better developed in skates and rays than in sharks  Likely a modified gill slit  Used to take in respiratory water in benthic skates and rays

Osteichthyes gills  Respiration via 4 pairs of gills  No individual openings to outside  Gills on each side covered by single, flap-like operculum  Respiration via 4 pairs of gills  No individual openings to outside  Gills on each side covered by single, flap-like operculum

Branchiostegal rays  Associated with operculum  Allow for expanding volume of mouth, pharynx chambers while keeping opercula closed  Accordian-like action

Osteichthyes gills  Each gill is actually a pair of rows of filaments each attached to the same gill arch  Gills not separated by septa - aseptate

Aseptate gills

Gill Structure

Gill fine structure  Filaments are not simple finger-like tissues  Each filament comprised of stacked plates or lamellae  Greatly increases surface area for interaction with water flowing across gills (water flows between lamellae)

Dual Respiratory Systems  Some fish have dual respiratory systems  Gills and lungs

Gills and lungs  Gills are main respiratory organs  Lungs serve as back-up system when gills no longer capable of providing gas exchange

Lungs

 Pouches branch off esophagus  Breathe air at surface or when they remain out of water

Paired lungs in lungfish

Lungfish lung - left

Lungfish lung  Lungs are mostly simple sacs with network of arteries, veins  Only the most intricate have beginnings of internal compartmentalization

Lungs  Paired lungs necessary because of alternating wet and dry periods  Become main respiratory organ when gills become useless  Paired lungs necessary because of alternating wet and dry periods  Become main respiratory organ when gills become useless

Lungs in many fish  Lungs are present in many of the more primitive fishes  Lungfish, bichir, gars, bowfin relatives, sturgeons  All have varying connections with esophagus  Lungs are present in many of the more primitive fishes  Lungfish, bichir, gars, bowfin relatives, sturgeons  All have varying connections with esophagus

Swim Bladder  Swim bladder probably arose from paired lungs of primitive fish  Lungs were present before swim bladder

Other respiratory organs  Mudskippers and European eels can derive significant amounts (10-90%) of oxygen via cutaneous respiration

Other respiratory organs  Walking catfishes (Clariidae) use suprabranchial arborescent organs to respire during their “walks”  Bush-like extensions from gills that do not collapse when out of water

Other respiratory organs  Mudskippers have folded and highly vascularized interior walls of opercula/gill chambers, diverticula in mouth and pharyngeal cavities (snakeheads also have the latter)

Other respiratory organs  Armored catfishes (Loricariidae) use thin-walled stomach for respiration  Loaches (Cobitidae) use middle/posterior portions of digestive tract