Osmoregulation

Many adaptations of marine organisms have to do with maintaining HOMEOSTASIS. The living machinery inside most organisms is sensitive and can operate properly only within a narrow range of conditions. Living things have therefore evolved ways to keep their internal environments within this range regardless of the external conditions

What physical factor of seawater can disrupt homeostatsis? SALINITY

You’d think that fish would never be thirsty; if he needs a drink, he just opens his mouth. But some fish never drink a drop! Let’s explore that !

Let’s review Osmosis- page 72 What is osmosis? What is a concentration gradient? Is osmosis “passive” or “active”? What is isotonic, hypotonic and hypertonic?

Fish are a good example of the problems of maintaining proper water and salt concentrations Freshwater fish can’t live in salt water and salt water fish can’t live in freshwater

salt water 35 ppt fresh water 0-5 ppt The problem of osmolarity:

salt water 35 ppt fresh water 0-5 ppt FISHES The problem of osmolarity: Hyper-osmotic Hypo-osmotic

Freshwater fish live in a HYPOTONIC environment The flesh of the fish contains more salt than does the water Diffusion and osmosis work to equalize salt concentrations Water will move from the freshwater into the fish’s tissues in order to balance the salt concentrations by osmosis

Freshwater fish DO NOT “drink” They take in water when they eat and move water across their gills To balance water, freshwater fish excrete large amounts of urine

salt water 35 ppt fishes are either: stenohaline - tolerant of limited range of osmolarity euryhaline - tolerant of wide range (where is this useful?) fresh water 0-5 ppt FISHES The problem of osmolarity: Hyper-osmotic Hypo-osmotic

How do MARINE fish osmoregulate? The tissues of marine fish have much lower in salt than they surrounding HYPERTONIC ocean Osmosis would dry them out, sending water OUT of their bodies Marine fish must drink ALL THE TIME in order to keep enough water in their body

Marine fish kidneys Retaining water would be an essential function of marine fish kidneys They also have CHLORIDE CELLS in their gills. These cells actively sequester salts from the blood and then pump the sodium and chloride out into the seawater

SHARKS are the exception… Sharks produce and retain a huge amount of a chemical called urea Urea is a soluble waste that animals normally get rid of This increases the solute concentration in the shark’s tissues at levels higher than in the seawater so water will diffuse into the shark’s body. This is their source of freshwater

Exception to the “shark” rule Bull shark Can live in both saltwater and freshwater Most sharks would die of water toxicity in freshwater Bull shark’s kidneys can adjust to the salinity

STENOHALINE Most fish are stenohaline They are restricted to either salt or fresh water and cannot survive in water with a different salt concentration than to that which they are adapted

SEMELPAROUS Salmon are semelparous Born in freshwater and move to saltwater and then return to freshwater Function of kidneys and gills

Osmotic conformers or Osmotic regulators? Osmoconformers- match their body osmolarity to their environment actively or passively. Most marine invertebrates (molluscs, worms) and hagfish are osmoconformers, although their ionic composition may be different from that of seawater. Ex. Sharks (to a limit) BULL SHARK, certain octopus

OSMOCONFORMERS Therefore, sharks are osmoconformers This means they maintain an osmotic balance with their environment A salt gland near the anus will excrete excess salt

Ocmoregulators- regulate their body osmolarity, which always stays constant Osmoregulators actively (requries energy) control salt concentrations despite the salt concentrations in the environment. Ex. Freshwater and marine fish, crab

BOZEMANBIOLOGY: osmoregulation sgHqMhttp:// sgHqM

STOP

1. osmo-conformers (hagfishes) maintain isosmotic conditions 2. salt supplementers (marine elasmobranches and coelacanths) high urea content and TMAO (trimethylamine oxide) low permeability to Na+, Cl- excrete excess Na+, Cl- How fish deal with being osmotic misfits

1. osmo-conformers (hagfishes) 2. salt supplementers (marine elasmobranches and coelacanths) 3. hyposmotics (marine teleosts) tend to lose water, replace by drinking gill cells pump in water, not salts How fish deal with being osmotic misfits

1. osmo-conformers (hagfishes) 2. salt supplementers (marine elasmobranches and coelacanths) 3. hyposmotics (marine teleosts) 4. hyperosmotics (freshwater fishes) excrete large volumes of water gill chloride cells pump in salts often euryhaline (striped bass, tilapia, drum) How fish deal with being osmotic misfits

anadromous - Pacific salmon, lamprey, shad Diadromous fishes fresh water salt water

anadromous - Pacific salmon, lamprey, shad Diadromous fishes fresh water salt water metamorphosis – cued to photoperiod, lunar cycle behavioral change (drinking) changes in kidney function

anadromous - Pacific salmon, lamprey, shad landlocked species (potamodromous) - reversion of salt-water tolerance Diadromous fishes fresh water

anadromous - Pacific salmon, lamprey, shad landlocked species (potamodromous) - reversion of salt-water tolerance catadromous - eels Diadromous fishes Credit: ICES salt water fresh water