BI451 Lecture 9 Buoyancy F23.pptx

BI451 Buoyancy in Fishes I. Buoyancy Archimedes Principle • an object completely or partly immersed in a fluid is “buoyed up” by a force equal to the weight of the fluid displaced Neutral Buoyancy (Weightlessness) • object displaces volume of water equal to its weight out of water • if density of...

BI451 Buoyancy in Fishes I. Buoyancy Archimedes Principle • an object completely or partly immersed in a fluid is “buoyed up” by a force equal to the weight of the fluid displaced Neutral Buoyancy (Weightlessness) • object displaces volume of water equal to its weight out of water • if density of object does not equal that of water it will rise or fall in water column • Positive buoyancy Specific gravity » density of object < density of water <1 » float • Negative buoyancy » density of object > density of water Four Strategies to Achieve Buoyancy in Fishes 1. Retention of Low-Density Compounds » fats, oils 2. Generation of ‘Lift’ during Forward Movement » ‘hydroplaning’ fins of sharks » heterocercal tail in sharks 3. Reduction of heavy (dense) tissues » reduce bone (SG 2.2) &/or muscle (SG1.06) density » cartilage (SG 1.1) 4. Use of gas bladders (swim bladders) » low density, gas filled space X-ray sb 1. Strategies to Achieve Buoyancy in Agnatha (i) Retention of low density compounds • Large fatty livers » lipids Specific Gravity = 0.9-0.92 (ii) Cartilaginous Skeleton Note: lack a gas bladder Petromyzon marinus 2. Strategies to Achieve Carcharinus plumbeus Buoyancy in Sharks (i) Retention of low density compounds • Body has SG = 1.026* » close to “neutral buoyancy” *SG of SW is 1.026. Most sharks are marine. • Large livers » lipids SG = 0.9-0.92 » squalene SG = 0.86 Note: lacks a gas bladder 2. Strategies to Achieve Buoyancy (ii) Generation of Lift in Sharks Carcharinus plumbeus • Heterocercal caudal fin • Pectoral Fins » Positions angle of attack • Streamlining to increase hydrodynamic efficiency » smaller fins (iii) Cartilaginous Skeleton (ancestral condition) Galeocerdo cuvier 3. Strategies to Achieve Buoyancy in (i) Retention of low density compounds • seldom seen in freshwater fishes Teleosts Lake trout (e.g. lake trout) • some marine fishes e.g. sablefish (Anoplopomatidae), rockfish (Scorpaeidae) (ii) Reduced skeletal-muscular system • deep sea fishes (< 1000 m depth) • no gas bladders • cartilaginous skeleton (SG = 1.1) derived condition • enlarged dilute, fluid filled cranial cavities » 50 % osmolarity of body fluids 3. Strategies to Achieve Buoyancy in Teleosts - The “Swimbladder” • “Gas Bladder” more appropriate terminology » fish do not use gas bladder to swim » seldom contains “air”. Composition different. • Arose from an ancestral lung in early jawed vertebrates Buoyancy • Many fish use gas bladders to achieve neutral buoyancy • Gas Bladder controls volume: weight ratio » positive buoyancy » negative buoyancy (Graham 1998) Evolution of the Gas Bladder Coelocanth? Lung/swimbladder but deepwater bottom fish ysostomous vs Physoclistous Gas Bl Gas Composition • varies amongst species • CO2, O2, N2 Gas Permeability • bladder wall relatively impermeable » guanine & hypoxanthine in submucosal layer Physostomous Gas Bladder (stoma = mouth) • Soft ray-finned teleosts (e.g. Salmonidae, Catistomidae, Cyprinidae, Anguillid Physoclistous Gas Bladder (“closed”) • Spiny ray finned teleosts. 2/3 of all fish. (e.g. Centrarchidae, Percidae) • Freed from the surface. Phystoclistous Phystostomous Lung: dual function Boyle’s Gas Law hysostomous vs Physoclistous Gas Bl Inflation of Physostomus Bladder • Gulping (swallowing) air at water surface » air diverted through “pneumatic duct” by increasing pressure in buccal cavity • Less effective in deep water due to high Pressure (P » P increases 1 atm for every 10 m descended » need large amounts of gas in deep waters to achieve neutral bouyancy Eel Air (From Pelster 1998. In Evans (ed). The Physiology of Fishes, 2 nd ed hysostomous vs Physoclistous Gas Bl Deflation of Physostomous Bladder by Reflux Pneumatic Sphincter • external pressure decreases  positive buoyancy • “Gass Puckreflex” (“gas spitting reflex”) » relax pneumatic sphincter  contraction of smooth muscle & elastic recoil of gas bladder wall + contraction of body wall  gas released into pneumatic duct  esophagus  negative buoyancy (sink) • Pneumatic Duct also has tissue which reabsorbs gas (O2) vented from gas bladder » well vascularized to “pick-up” resorbed gas (From Pelster 1998. In Evans (ed). The Physiology of Fishes, 2 nd ed). hysostomous vs Physoclistous Gas Bl Physoclistous Gas Bladder (“closed”) • Spiny ray finned teleosts (e.g. Centrarchidae, Percidae) Volume Control • Richly vascularized gas bladder = “Rete mirabile” (wonderful net) Galen 2nd century Capillary bed; highly vascularized structure » in both physostomous & physoclistous fishes • Gas Gland also in both but variable in size Physoclistous Gas Bladders missing pneumatic duct • Gas Gland - secretion of gas • Oval Patch - resorption of gas (From Pelster 1998. In Evans (ed). The Physiology of Fishes, 2 nd ed). GASGLAND & RETE Mirabile Slide 18 from respiration lecture 1. Counter Current Multiplier • maximizes O2 uptake by maintaining relatively stable PO2 gradient Fig. 12-8from Hill & Wyse VIEW slide 11 and 16 cardiovascu SALTING OUT Low salt High salt [N2] PN “Rete Mirabile” Arterial Capillary PO2 40 pH 7.82 PO2 281 pH 7.33 Venous Capillary PO2 44 pH 7.64 PO2 293 pH 7.1 FUNCTION of the GAS GLAND Rete Capillaries Afferent • Lactate  salting out of CO2, N2, O2 • H+  Three effects » ‘Root-off’ Effect » Bohr Shift » Combine with HCO3- to generate CO2 Efferent • Slow “Root-on” effect » ~ 10 seconds to restore Hb-O2 affinity » delay ensures PO2 sufficiently high to maintain efferent to afferent capillary PO2 gradient “Counter-Current Multiplier” Counter Current Multiplier Effect • Can achieve gas partial pressures up to 300 atmospheres. • Diffusion of gases from venous (efferent) to arterial (afferent) capillaries ensures very high gas partial pressures at swim bladder • Multiplication proportional to length of retial capillaries » longer capillaries the more gas unloaded » correlation with deeper living fishes. Why? e.g. Anguilla anguilla - Root-OFF » PO2 = 40-281 mm Hg » pH = 7.82 to 7.33 (Root-off)