IntroductionHomeostasisThermal regulation hormones – endocrine systemEnzymes osmoregulatory processes Occasionally marine organisms just “pick up

and move” if environmental conditions are unfavorable

DefinitionsHomeostasis = maintaining steady state

equilibrium in the internal environment of an organisms

Solute homeostasis = maintaining equilibrium with respect to solute (ionic and neutral solutes) concentrations

Water homeostasis = maintaining equilibrium with respect to the amount of water retained in the body fluids and tissues

Definitions, continuedOsmotic concentration Total concentration of all solutes in an

aqueous solutionmeasured in units of osmolalosmolals = 1 mole of solute/liter of water

milliosmolals = 1/1000th of one osmolal

Osmoregulation in different environments

Challenge to homeostasis depends onsteady state concentration of solutes in the

body fluids and tissues as well asconcentration of solutes in the external

environment marine systems: environment concentration = 34 -

36 parts per thousand salinity = 1000 mosm/l freshwater systems: environment concentration < 3

ppt salinity = 1 - 10 mosm/l Estuaries: vary with tides and precipitation

Hypertonic vs Hypotonic

Osmoregulatory StrategiesHypoosmotic – saltwater fish Hyperosmotic – freshwater fishIsosmotic: regulation of specific ionsIsosmotic: nearly isoionic, osmoconformers

Cells swell or shrink

Body fluid osmotic concentrations

Osmoregulation in different environments

Each species has a range of environmental osmotic conditions in which it can function:stenohaline - tolerate a narrow range of salinities in

external environment - either marine or freshwater ranges

euryhaline - tolerate a wide range of salinities in external environment - fresh to salineshort term changes: estuarine - 10 - 32 ppt

intertidal - 25 - 40

long term changes: diadromous fishes

Salmon migrating from sea to river

300px-Jumping_Salmon fish migration wikipedia

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External Medium, mOsm/Kg

Body Fluid, mOsm/Kg

Shore Crab

Decorator crab

Isosmotic Line

Freshwater Fish

Marine Fish

Fiddler Crab

Hyperosmotic regulator

Osmoconformer

Hypo-osmotic regulator

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Invertebrates SW

Invertebrates FW

Sharks SW

Sharks FW

Teleost Fish SW

Teleost Fish FW

Amphibia

Reptiles, Birds, Mammals

Body Fluid, mOsm/Kg

Ions Urea & TMAO

SeawaterBrackish waterFresh water

Osmoregulators and osmosconformers

Marine fish face two problems: they tend to lose water and gain ions.

Freshwater fish face two problems: they tend to lose ions and gain water.

Salt Excreting Glands Marine birds and

reptiles cannot make a concentrated urine.

Birds use nasal glands that release salt excretions into the nasal passages.

Sea turtles have modified tear ducts that secrete salt into the orbit of the eye.

Nitrogenous WastesAmmoniaUreaUric acid

What about rapid ion flux?

EuryhalineShort-term fluctuations in osmotic state of

environment, e.g. in intertidal zone or in estuaries

salinity can range from 10 to 34 ppt with daily tidesthese fish have both kinds of chloride cells

when salinity is low, operate more like FW fishes when salinity is high, operate like marine fishes kidneys function only under low salinity conditions

European eel & shore crab

EuryhalineDiadromous fishes - spend part of life in salt

water, part in freshwater catadromous (migrate seaward) anadromous (migrate up river)hormone-mediated changes associated with

metamorphosis – convert from FW adaptations to SW or vice

versa, depending on direction of migration

How to reduce stress in stressed fish?Minimize the osmotic challenge by placing

fish in conditions that are isosmoticadd salt to freshwater, e.g. in transporting fish

or when exposing them to some other short-term challenge

dilute saltwater for same situation with marine species

Temperature effects on fishTemperature exhibits the greatest influence

on fishAffects metabolismAffects digestionSignals reproductive maturation and

behavior

Fish are conformers (well, sort of...)Body temperature is that of the environmentEach species has particular range of

temperatures that they can tolerate and that are optimal

Big difference between what you can tolerate and what you thrive in...

Hot FishesSome fish can maintain body temperature greater

than ambient - tunas, billfishes, relatives (nearly endothermic)

Use retia (similar to rete mirable) in swimming muscles to conserve heat, exchange O2, etc.

Red muscle is medial rather than distalBillfishes have warm brains - heat organ from

muscles around eye

Freezing Resistance

I10-33-Antarcticfish universe-review.ca/

Solutions in Antarctic FishAnti-freeze compounds (AFP)Peptides and glycopeptidesBoth rich in alanineMolecules adsorb (attach to) surface of ice intefere with ice crystal growth – disrupt matrixProtects cell membranesIce can rupture cells

Antifreeze