Re:Grounding electrodes

     I am a fisheries biologist, and in freshwater we use electrofishing 
     gear to collect fish--sending the appropriate current through the 
     water temporarily stuns fish and brings them to the surface, where 
     they are easily collected.
     The following paragraph is from a reference, "Fisheries Techniques" 
     edited by Larry Nielsen and David Johnson, which may help to answer 
     the following APD posts:
     >> The fish will have a very very low resistance, a lot lower than the
     >> water.  
     >Would you state for the record the actual resistance of the fish in
     >question and the resistance of the water?  
     from page 150 of "Fisheries Techniques"...
     "Because a fish has resistance, a given current density at one end 
     will result in a lowered density at the other, producing a voltage 
     gradient in the fish.  Voltage gradients of 0.1 to 1.0 volts/cm are 
     most effective for stunning fish; these gradients can be maintained in 
     freshwaters of normal conductivity (100-500 micromhos/cm) by adjusting 
     circuit voltage to produce a current of 3-6 amperes.  At high 
     conductivities, water becomes less resistive than fish and the current 
     tends to flow around them, resulting in little or no voltage effect; 
     this is the reason that electrofishing is not used in brackish or salt 
     water.  At low conductivities (less than 100 micromhos/cm), the water 
     is more resistant than fish, but the electrical field is limited to 
     the immediate area of trhe electrode.  When this occurs,a fish may not 
     be affected until it touches the electrode--then it suddenly receives 
     a high voltage gradient and dies".
     It goes on to say distilled water has a conductivity of 0.5-4.0 
     micromhos/cm, most freshwater bodies are between 50-1,500 micromhos/cm 
     and saltwater is 500 times more conductive than freshwater.
     From this discussion, it appears some aquaria have water more 
     conductive than the fish, while others are not, depending on the 
     mineral content.