See these from SRAC
http://srac.tamu.edu/index.cfm?catid=13Water quality
Selection of a site for red drum
production must be based on the
knowledge that adults can survive in
either freshwater or saltwater. The
larvae require salinities of 25 to 35
ppt for at least their first 30 days. In
addition, red drum require water
with a calcium content greater than
100 ppm and a chloride content
greater than 150 ppm for good survival.
For optimum growth the calcium
content should be more than
150 ppm and the chloride content
greater than 1,000 ppm.
Temperature
Red drum cannot tolerate extended
periods of time when water temperatures
temperatures
are below 40°F. Selection of a
site must consider the normal minimum
(not average) low temperature
in an area. Heated water can be
used but it is not readily available in
most areas. Red drum will tolerate
low salinity water, but survival is
reduced in water below 50°F and
lower than 5 ppt salinity. Air
temperature directly affects water
temperature; therefore, if yearround
water temperature data are
not available, check the air temperature
data from the closest reporting
station. If available use the frequency
and duration of freezing temperatures
rather than average daily
temperatures. A few consecutive
days of freezing temperatures can
destroy an entire crop of red drum
in unheated outdoor raceways or ponds.