This intolerance of catfish to abrupt
increases in pH has important practical
considerations. Most newly hatched
catfish fry are held for several days
in hatchery tanks supplied with flowthrough
groundwater with a pH near
8.0. Fry are then transferred to a transport
tank (usually filled with water from
the same source used in the hatchery)
and then stocked into a nursery pond
for further growth. Nursery pond pH
cycles daily, and if fish are transferred
to the nursery pond during the afternoon
when pH is usually highest, many
fish may quickly die. The solution is
simple: First measure the pH of the
water in both the transport tank and the
pond, and then transfer fish only when
the pH of the receiving water is very
near, or below, that of the transport
tank water. Pond pH is usually lowest a
few hours after dawn, so this is usually
the best time to transfer fry