BIOLOGY 457/657 PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS

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BIOLOGY 457/657PHYSIOLOGY OF MARINE ESTUARINE
ANIMALS

• February 18, 2004
• Osmoregulation in Marine Vertebrates

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A COMPARISON OF VERTEBRATE INVERTEBRATE
OSMOREGULATION
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VERTEBRATE OSMOREGULATION OVERVIEW
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VERTEBRATE OSMOREGULATION

• Two Major Vertebrate Groups
• Fish Amphibians (evolved in water)
• Reptiles, Birds, Mammals (evolved in air to
  these animals, seawater is a desert)
• It is thought that the first modern vertebrates
  evolved in freshwater, because their solute
  levels are low. However, some primitive fishes
  have solute concentrations very similar to
  seawater.
• Modern fishes must have returned to the ocean
  from freshwater. Some fish alternate between
  habitats
• Anadromous breed in FW, live as adults in SW
• Catadromous breed in SW, live as adults in
  estuaries

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OSMOREGULATION IN FISHES
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FISHES I CYCLOSTOMES

• Cyclostomes (Class Agnatha) are jawless,
  primitive fish.
• Hagfishes (marine) are isosmotic, using FAA to
  adjust ?.
• Lampreys (freshwater or anadromous)
• are like teleosts, with excellent Na
• transport systems Kt (Na) 0.13
• mM in gill tissue.

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FISHES II ELASMOBRANCHS

• Elasmobranchs (Class Condrichthyes sharks
  rays) are generally marine, with a few freshwater
  species (e.g. Amazon ray, bull sharks of Lake
  Nicaragua)
• Their inorganic solute
• concentrations are similar
• to those of teleosts (bony
• fishes). The deficit is
• made up using organic solutes.

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ELASMOBRANCHS (2)

• The shark kidney actually reabsorbs urea, back
  into the blood. Shark proteins are highly
  tolerant of elevated urea.
• Total osmoticity is usually slightly gt 1000 mOsm,
  so water continually enters by osmosis (for
  metabolism and urine formation)
• Freshwater elasmobranchs excrete urea, reduce
  drinking, and increase salt uptake (perhaps by
  the gills or digestive tract).

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CLASS CROSSOPTERYGII

• The lobe-fin fishes, represented today only by
  the coelacanth (genus Latimeria), are ancestral
  to all terrestrial vertebrates.
• Physiologically (with regard to osmoregulation),
  they are like the elasmobranchs.

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CLASS TELEOSTII (Bony Fishes)

• All teleosts have similar blood osmolality, about
  25 to 40 of seawater. Many species occupy both
  fresh and salt water.
• The Osmotic Problem

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MARINE FISHES

• Are hyposmotic
• LOSE water
• through the gills,
• body surface, and
• in wastes.
• DRINK seawater
• (a flounder drinks
• about 1 of its
• mass per hour)
• Are hypoionic
• GAIN salts across gills, body surface, and in
  food.
• EXCRETE salts (Na, Cl-) across gills. Other ions
  (K, Ca, Mg, SO4) are excreted by the kidney
  in the hypotonic urine, by tubular secretion.

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MARINE FISHES

• Chloride Cells Sites of ion transport in fish
  gills.
• Cations (Na, K) are cotransported with Cl- ions
  at the basal surface. Cl- passive passes out of
  anion channels at the apical surface, and Na
  follows through leaky tight junctions between
  cells.

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FRESHWATER FISHES

• Are hyperosmotic, and gain water in food, across
  the gill, and across the body surface.
• Excrete a dilute, copious urine (up to 400
  ml/kg/day).
• Are hyperionic, and lose salts in urine and by
  diffusion.
• Import salts in diet and by active transport at
  the gill.

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EURYHALINE FISHES

• Example Xiphister (blenny)
• (Must shift between modes)

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CLASS AMPHIBIA

• Most amphibians are freshwater or terrestrial,
  but a few are euryhaline. Most are
  ammonicotelic, but some euryhaline species are
  ureotelic. Euryhaline species actually
  osmoconform at elevated salinities, using ions or
  urea.

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CLASS REPTILIA

• Reptiles are essentially terrestrial, but some
  species live in freshwater, marine, or estuarine
  habitats. All are uricotelic. However, the
  estuarine diamondback terrapin (Malaclemys)
  actually uses urea as an osmotic effector!
• Marine species (turtles, crocodiles, snakes,
  iguana) produce an isotonic urine and excrete
  salt using extrarenal salt glands.

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CLASS REPTILIA

• SALT GLANDS
• Marine Iguana nasal gland, sneezes
• Snakes, Turtles - supraorbital gland, drain
  secretions into the orbit (turtles) or oral
  cavity (snakes)
• Crocodiles sublingual salt glands, drain into
  oral cavity

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CLASS AVES

• Like reptiles, birds are essentially terrestrial
  animals, but have many successful marine species
  (and are more diverse than any other
  air-breathing vertebrate). All reproduce on
  land. Urine is hypotonic or isotonic. All are
  uricotelic.
• Marine birds have a large extrarenal
• pair of salt glands external to the
• skull, producing a concentrated solution of NaCl.

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CLASS AVES

• Salt-gland secretion by a herring gull. The
  gland uses a countercurrent mechanism to
  concentrate salt in the secretion, and can
  transport salt at up to 20x the rate (per gram of
  tissue) as a human kidney.

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CLASS MAMMALIA

• All marine mammals are secondarily evolved from
  terrestrial ancestors. They form a diverse group
  of animals pinnipeds, sirenians, otters, and
  cetaceans.
• Many marine mammals gain water from their food
  (e.g. other vertebrates, teleosts). Their
  kidneys can produce urine that is hypertonic NOT
  ONLY to the blood, BUT ALSO to seawater.

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CLASS MAMMALIA
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CLASS MAMMALIA