Soft internal anatomy, respiration, & osmoregulation Lecture 4

Skeletal (voluntary) muscle Relatively high proportion of fish is muscle Muscle segmented into myomeres Fibrous septa attach to skin and backbone

Skeletal (voluntary) muscle Myosepta White vs. Red Muscle

White muscle White muscle—greater proportion Low blood supply Burst swimming—anaerobic Few mitochondria Fatigues quickly Burns glycogen Energy storage Muscle mass varies seasonally 4 min The fishing effect

Red muscle Red muscle—high blood supply Sustained swimming—aerobic respiration Many mitochondria Lipids used as energy source May also power pectoral fins

Alimentary canal—how is it different? Esophagus—often has tastebuds and very flexible Length of intestine varies Elasmobranchs—spiral valve Pyloric caeca—

Countercurrent Exchange Systems Rete Mirabile—arterial and venous capillaries are closely associated Flowing in opposite direction Designed to retain heat, ions, or gases in certain tissues or areas of the body 2 units of a Rete Mirabile

Countercurrent Exchange Systems Example: countercurrent heat exchange Endothermic fishes Rete Mirabile Heat flows from vein to artery, as long as a gradient exists 20o 15o 10o 5o Muscles in body core—heat produced Gills—heat lost

Concurrent Exchange Systems Muscles in body core—heat produced Gills—heat lost

Swim bladder—Buoyancy control Originally evolved as a lung Two types of swim bladder arrangement Physostomus fishes have pneumatic duct More primitive Gulp and burp air to regulate Physoclistous regulates filling by adding or removing gases from blood

Swim bladder—Physoclistous Gases diffuse in/out of bladder—down concentration gradient Partial pressure gradient—the pressure of a gas on a mixture Oval— Stretch receptors help regulate Gas Gland— Oval Gas gland Rete Mirabile Swim bladder

Swim bladder—Physoclistous One of 1000+ capillaries entering gas gland through rete mirabile Rete Mirabile Gas Gland

Swim bladder—Physoclistous Cells in gas gland deposit lactate and H+ into capillaries Reduced pH → hemoglobin dumps O2 Lactate (solute) reduces gas solubility H+ + HCO3- → CO2 + H2O ↑ Partial pressure of O2, CO2, and N2 Some gas molecules diffuse across Problem: concentration and pressure of gases still not high enough. Most gas does not pass into swim bladder. Gas Gland

Swim bladder—Physoclistous Solution: Countercurrent Concentration Rete Mirabile retains gases Gas concentration ↑ Equilibrium reached Gas Gland

Swim bladder—depth changes Volume of a gas changes with pressure 33 feet rise = double the volume 66 feet rise = Barotrauma—

Swim bladder—other uses Sound production using a sonic muscle Muscles rapidly contract (vibrate) Extrinsic sonic muscle—still attached to body Sciaendae Intrinsic sonic muscle—only attached to bladder Triglidae, Batrachoididae http://core.ecu.edu/BIOL/luczkovichj/fishsounds/fish_sounds.htm http://www.fishecology.org/soniferous/fishsongsringtones.htm Purpose of sound production? Extrinsic

Intrinsic

Swim bladder—other uses Sound waves passing through fish vibrate swim bladder Hearing specialists have connection from swim bladder to inner ear More sensitive hearing Weberian ossicles

Cardiovascular system Sinus venosus Atrium 4 “chambered” heart Ventral Aorta Valves prevent backflow Bulbus arteriosus Ventricle Fish hearts relatively small and size varies by species Heart  ____________  ____________  Heart Dorsal aorta is main artery to body

Cardiovascular system Fish have a relatively small blood volume Elasmobranchs somewhat larger Red blood cell size varies by species Up to 5x larger than humans Contain nucleus

Challenges of respiration in water Much lower O2 concentration in water As temperature increases O2 decreases O2 can be spatially variable Salt water holds less O2 than freshwater Gills require more energy than lungs Poeciliidae Aquatic surface respiration

Same system used by many species when feeding Ventilation Fish pass water over gills to extract O2 O2 diffuses across membrane down gradient Ventilation achieved using mouth, buccal chamber, and operculum Same system used by many species when feeding Mouth open Buccal chamber expanding Opercular valve shut Mouth closed contracting valve open

Gills Efficient at extracting O2 from water Surface area varies 7-fold Large surface area Thin epithelial membrane Countercurrent blood flow Surface area varies 7-fold

Gills—countercurrent blood flow O2 only diffuses if concentration gradient exists Countercurrent flow  O2 in water always higher than blood

Other types of ventilation Ram ventilation— Some pelagic predators dependent Must keep swimming Many species use both methods Spiracles in elasmobranchs—

Endothermy in Fishes

Osmoregulation Osmoregulation— Fish are osmoregulators— Thin gill membranes allow gas transfer, but this comes at a cost……….? Why do freshwater and marine fishes have opposite problems?

Osmoregulation—fresh vs. saltwater H2O Salts Diffusion Active transport Salts Dilute urine Drink Concentrated

Osmoregulation—kidneys & bladder Freshwater fish have larger kidneys Retain solutes  blood Salts may also be reabsorbed through bladder Saltwater fish have smaller kidneys Retain water  blood Water may also be reabsorbed through bladder Kidneys also remove nitrogenous waste from blood Ammonia Most is removed at the gills

Osmoregulation—gills Mitochondrial rich cells in gills transport ions (chloride cells) Freshwater fish Chloride cells take up ions from water Na+, Cl-, Ca2+ Saltwater fish Na+, Cl- removed; Ca2+ brought in Diadromous fishes adjust cell function during migration

Subclass Elasmobranchii—Osmoregulation Most of fish diet is protein  ammonia NH3 (toxic) Elasmobranchs convert NH3  urea Retained in blood (solute) Water gained at gills Rectal gland— Coelacanth Salt water Gill membrane Blood vessel Urea increases osmotic pressure