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Lecture 20

Organismal Physiology_Lecture 20.docx

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Western University
Biology 2601A/B
Tamsen Taylor

Organismal Physiology Lecture No. 20: Water, Salt & Fish II th Tuesday November 20 , 2012 Introduction: -In terms of water salinity, freshwater is 0.05% salty, brackish water is 0.05-3%, saline water is 3-5%, and brine is >5%. The gram weight of solute is relatively constant in sea surface salinity. However, the arctic/Antarctic ocean is said to have slightly less than average salt content, much like the salt content of the Mediterranean is slightly greater than average. Ion ratios in salt water are also relatively stable. Hard water is defined as water of low salinity, often derived from the drainage of calcareous earth. Soft water has lower salinity and is derived from acidic igneous rock. The Situation For A Freshwater Teleost: -In freshwater teleosts that are hyperosmotic to the ambient water (like the ble-gill), the following processes are expected to happen: The salt and water content in freshwater and food are ingested through the mouth (don’t drink too much water like saltwater fish), water uptake by osmosis and salt loss by diffusion occurs across the gill surface (no external gills, they are covered by operculum), salt and water content is excreted through feces, large amounts of urine (very hypoosmotic to blood plasma) is excreted through urination, and the active uptake of Na and Cl from the water is done across the gill surface (through chloride cells). Gills As Exchange Organs & NaCl Uptake: -In addition to exchanging gaseous CO and O ,2gill sur2aces are used to take up salts from the environment and process a large volume at that, even though there is no
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