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<br />" 19805
<br />
<br />Electrical Anesthesia
<br />
<br />69
<br />
<br />,
<br />
<br />(1) It was successful in immobilizing all
<br />sizes of chinook captured and had no notice-
<br />able side effects (several fish were dissected
<br />after shocking and no hemorrhaging in the
<br />muscle tissues or internal organs was de-
<br />tected), (2) The fish were handled only once.
<br />(3) Fish processing time was less than one
<br />minute, (4) Large anesthetic and recovery
<br />tanks were not needed. (5) Minimal deck space
<br />was needed to process the fish, thus a smaller
<br />vessel could be utilized. (6) Potential residual
<br />chemical effects on the fish and their predators
<br />were eliminated.
<br />
<br />Photographs of the basket and the electrical
<br />control box are shown in Fig. 1 and 2; basket
<br />construction and the wiring diagram is de-
<br />picted in Fig, 3 and 4. A rheostat and potenti-
<br />ometer' of 250-ohm rating were used to regu-
<br />late the voltage to the landing basket. These
<br />instruments provided excellent control of vol-
<br />tage in waters of 16-18%0 salinity near Ju-
<br />neau. However, in the more conductive waters
<br />of Icy Strait (24%0), little control of the voltage
<br />was realized, and the full voltage remaining in
<br />the 12 volt battery was automatically applied
<br />
<br />to the landi g basket regardless of where the
<br />controls we e set, We believe that voltage
<br />regulating nstruments of higher capacity
<br />would provi e better control of voltage in wa-
<br />ters of hig er salinity. Power drain on the
<br />batteries wa minimal; without recharge, they
<br />retained cha ges of over 10 volts at the end of
<br />the month-l ng study.
<br />
<br />Reference Cited
<br />
<br />Hartley, W, G. 1967, Electronarcosis of fish for han-
<br />dling. Pa s 251-255 in R. Vibert, ed., Fishing
<br />with elect icity, its application to biology and
<br />managem nt, contributions to a symposium.
<br />European Inland Fisheries Advisory Commis-
<br />sion, FAO Fishing News (Books) Ltd., London,
<br />England.
<br />
<br />Gary K. Gun trom and Mike Bethers, Alaska
<br />Department 0 Fish and Game, Island Center Bldg.,
<br />P,O. Box 20, ouglas, Alaska 99824
<br />
<br />..,.
<br />
<br />Practical Formulas for Computing Water Exchange Rates
<br />
<br />Reported data on water exchanges rates in
<br />aquaria and aquaculture systems are often
<br />confusing because different methods of ex-
<br />change result in different amounts of water
<br />replacement. For example, in a batch or dis-
<br />crete replacement, if half the volume of water
<br />is removed and then replaced with new water,
<br />the tank will have 50% new water. However,
<br />in a continuous flow system, if 50% new water
<br />is added gradually to a full tank and com-
<br />pletely mixed water is allowed to spill out,
<br />some new water will go out with the old water,
<br />and the tank will retain only 39% new water.
<br />This difference is usually not critical, and pub~
<br />lications may avoid the issue by stating "50%
<br />of tank volume was added per day," instead of
<br />the more ambiguous "50% of the water was
<br />exchanged."
<br />For some applications, it is important to
<br />
<br />Prog, Fish-Cult. 47(1), January, 19805
<br />
<br />know exactl how much water has been ex-
<br />changed. Ex mples include dilution of antibi-
<br />otics and oth r medications, and optimum di-
<br />lution of exc eted wastes.
<br />Sprague (1 69) plotted the times for replac-
<br />ing 50, 75, 9 , 95, and 99% of existing water
<br />against flow rates in continuous systems. A
<br />more compre ensive formula for determining
<br />dilution in t e Great Lakes is presented by
<br />Rainey (1967). Most aquarium and aquacul-
<br />ture systems re not as complex as Lake Erie,
<br />and a gener I formula can be derived from
<br />Rainey's equ tions for simple cases of con-
<br />tinuous flow ilution, Three arrangements of
<br />this formula re:
<br />
<br />1) F = 1_(lIe'fRJV) = 1_(e-TRJV)
<br />2) T = -In(I-F)'VIR
<br />3) R = -In(I-F)'Vrr
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