Hydromineral Balance read pp' 8995 in text

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Hydromineral Balance read pp. 89-95 in text Two
issues - Osmotic regulation total salt
balance determines movement of water Water
moves through semi-permeable membranes such that
salt concentration is same inside and out

• Ionic regulation
• Specific ions like sodium Na, Cl-, Mg, SO4-2

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Osmoregulation 4 strategies (table 7.1 and
Fig. 7.3)

• Osmoconformer
• No regulation
• Hagfish
• stenohaline tolerates only a narrow range of
  salinity
• occupies deep marine habitats
• Use Urea and TMAO to increase osmotic pressure
• Marine Chondrichthyes
• Regulate salt concentration at 1/3 sea water
• Store Urea
• manufacture Trimethylamine Oxide (TMAO)
• Excrete NaCl- through rectal gland
• Active transport process

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Coelacanth stores urea in blood has rectal
gland Only living boney fish that does
this gives insight into early boney fish
evolution
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• More stratgegies for Osmoregulation
• Hypo-osmotic
• Marine Actinopterygians and Lamprey
• Problem is that they lose water over membranes
• So they drink seawater
• brings in too much Na Cl-
• Excrete these salts in gills
• Chloride cells site of active transport
• energetically expensive
• See box 7.2 and Fig. 6.2
• Sea water also has lots of Mg2 and SO42-
• Kidneys are site of active transport
• Fish kidneys cannot produce concentrated urine

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• Hyperosmotic regulation
• Freshwater actinopterygians, FW elasmobranchs,
  and lamprey
• Problem is water entering body
• Produce dilute urine Up to 1/3 of body mass
  per day
• Take up salts from food and gills
• gills contain chloride cells for active
  transport into body
• Na and Cl-

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Ionic Regulation Hagfish Maintains high
Na transports Mg2 and SO42- in
urine Elasmobranchs rectal gland to excrete
Na and Cl- Marine teleosts Na Cl- with
gills Mg2 and SO42- with kidneys
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Ionic regulation in Freshwater Teleosts Kidneys
help with some retention of monovalent and
divalent ions Gills exchange of Na for NH4
exchange of Cl- for HC03- Good for ionic
regulation Elimination of nitrogenous
wastes Maintains acid-base balance Acid rain
poses problem
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Diadromus fishes Catadromus moves from marine
to FW to marine eels often tropical Anadromus
moves from FW to Marine back to
FW salmonids lampreys striped
bass American shad often temperate zone
Problems for osmoregulation Diadromus fishes
show changes in membrane permeability Active
transport of ions changes direction These
changes are mediated through hormone
changes Salmonid smolts studied best increased
photoperiod results in increased thyroxin that
increases cortisol resulting in an increase in
Chloride cells Prolactin is a similar
freshwater hormone results in reduced loss of
Na over gills
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When FW fish is place in SW, it loses weight,
begins drinking sea water, and makes chloride
cells Energetically costly