Lecture 8 Physiology 1. Buoyancy a. Gas - Gut - Gas bladder b. Chemical- Liver - Muscles 2. Respiration a. Water respiration b. Aerial respiration 3. Thermal regulation 4. Circulation 5. Osmoregulation Buoyancy • maintaining vertical position in the water column • potentially energetically costly • many primitive fishes had lungs • in more advanced lineages, lost respiratory function • became gas bladder Buoyancy gas bladder (aka swim bladder) • used to regulate buoyancy as well as sound production & detection in some fishes • respiratory function in primitive fishes stretch receptors • buoyancy is controlled by changing size of gas bladder Buoyancy Respiratory gas bladder • gut connection • in order to maintain buoyancy, have to keep gulping • highly vascularized and Gar (Lepisosteiformes) subdivided • adapted for gas exchange Bowfin (Amiformes) Buoyancy Physostomous gas bladder – primitive sac • derived as outpocket from gut • vascularized • retains connection to gut via the pneumatic duct • gas enters via gulping and/or diffusion from gas gland • gas exits via pneumatic duct • fine control difficult Buoyancy Physoclistous gas bladders • sealed off from the gut • no pneumatic duct • gas enters and exits via blood (gas gland & oval) • excess gas offloaded via gills • found in more derived teleost groups Buoyancy gas bladder components gas gland: inflates gas bladder • by diffusion rete mirabile: looping bundle of arterial & venous capillaries • generates concentration gradient oval/pneumatic duct: removes gas Buoyancy Bohr and Root Efffects Bohr effect: hemoglobin’s affinity for oxygen is inversely related to acidity and CO2 concentration Root effect: hemoglobin dumps O2 quickly in acidic environment but rebinds O2 relatively slowly when the pH increases Buoyancy Inflating gas bladder occurs by diffusion, not by active transport… Gas gland • Secretes lactic acid (disassociates into H+ and lactate) • hemoglobin dump O2 via Bohr and Root effects • raises partial pressure of O2 • reduces solubility of gases in solution • leads to gas bubble formation (including CO2 ) -> Drives gas bubbles into gas bladder Buoyancy Deflating gas bladder occurs by diffusion, not by active transport… Oval(e) • Reabsorptive region of the gas bladder • Muscles contract or relax to expose vascularized area for gas reabsorption • Also control blood flow to this area -> Allows gas bubbles to exit gas bladder Buoyancy Chemical Pelagic elasmobranches maintain high levels of low density lipids in their livers • 20-30% of their body weight • non-compressible • great for changing depths quickly • energetically costly to produce • can metabolize during starvation periods Buoyancy Chemical Large pelagic sharks were commercially harvested for the oil rendered from their livers… Commercial fisherman talking about basking shark oil “ the oil was absolutely beautiful. A penny tossed in a 15 foot- deep, 15,000-gallon tank of oil took five minutes to hit the bottom, and you could see it all the way down.” cartilage vs bone Buoyancy basking shark that weighs - specific gravity is 1.1 Chemical 1000kg in the air weighs vs 2 (~55% less dense) 3.3kg in water Pleurogrammma antarcticum Buoyancy Chemical Nototheniidae (family of Antarctic icefishes) • predominantly benthic • some pelagic spp. • lack gas bladder like their ancestors • high proportion of skeleton is cartilaginous Dissostichus mawsoni • lipid deposits throughout body, including blubber layer under the skin, and fat cells between muscle fibers Pagothenia borchgrevinki Respiration Water respiration Things to consider… • Water contains considerably less O2 than air (~1% compared to 20% ) High density and viscosity • Sea water holds 25% less means that more energy is O2 than freshwater required to simply move • diminished solubility water across the of gases due to respiratory surfaces… increased [salts] • O2 is lowest in warm, marine environments Respiration Water respiration Cabezon – suction respiration Barracuda - ram respiration Respiration Fish body form ram suction Respiration Water respiration Gills • very efficient at extracting oxygen from water • high surface area • countercurrent exchange Respiration Water respiration Countercurrent exchange Water respiration Respiration blood in lamellae flows in opposite direction to water • as blood picks up O2 from water, moves toward area where the adjacent water has even higher [O2] Respiration Aerial respiration • evolved 400 mybp • has arisen at least 38 times since then • most successful colonized land (tetrapods) • over 370 extant fishes are air breathers Respiration Aerial respiration Amphibious fishes • Gill structure well supported to prevent collapse • Percolate water in their buccal & opercular cavities • Skin often scaleless & well vascularized for gas exchange Respiration Aerial respiration gourami & fighting fish Osphronemidae Labyrinthine plates: highly vascularized chamber that can hold air and allow for gas exchange Respiration Respiration Aerial respiration African lungfish Australian lungfish South American lungfish facultative airbreather: obligate airbreathers: supplements respiratory require access to air to needs with air sufficiently exchange gases Circulation The heart is located posterior and ventral to the gills in all fishes black = blood w/ low O2 content white = blood w/ high O2 content Circulation Conus Circulation conus arteriosus replaced by the nonmuscular bulbus arteriosus • elastic reservoir that dampens pressure oscillations • provides continuous blood supply Thermal regulation Endothermic fishes • large animals • modified circulatory system with counter current exchange to retain heat • “rete” Thermal regulation eye muscle generates heat • loss of contractile fibers Thermal regulation typical fish tuna • countercurrent exchange Thermal regulation tuna billfish red muscle Thunniform swimming likely a preadaption for circulatory arrangements to maintain elevated body temperatures… Thermal regulation Whole body endothermy wegner et al. 2015 Osmoregulation – Fresh water fishes hyperosmotic to environment • gain water through gills & skin • lose solutes by diffusion across gills • actively transport salts back into blood and produce copious amounts of dilute urine Osmoregulation – Fresh water fishes hyperosmotic to environment • gain water through gills & skin • lose solutes by diffusion across gills • actively transport salts back into blood and produce copious amounts of dilute urine Osmoregulation – Marine teleosts hypoosmotic to environment • loose water through gills & skin • gain solutes by diffusion across gills • actively transport salts out of gills into sea water and minuscule amounts of isosmotic urine Osmoregulation – Marine teleosts hypoosmotic to environment • loose water through gills & skin • gain solutes by diffusion across gills • actively transport salts out of gills into sea water and minuscule amounts of isosmotic urine Osmoregulation – Cellular level Freshwater Mitochondria rich cells of the gills actively pump salts across basolateral membrane Osmoregulation – Cellular level Marine Mitochondria rich cells of the gills actively pump salts across basolateral membrane Osmoregulation - Sharks trimethlyamine oxide (TMAO) • stabilizes protein hyperosmotic to environment • convert wastes into urea & retain in blood with TMAO • gills impermeable to both • gains H2O via diffusion across gills • dump excess salts via rectal gland.