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.
The physiological basis for the insensitivity
of catfish fry to rapid increases in
pH is unknown and a similar response
may occur in other fish or crustacean
species. In the absence of additional
information farmers should assume that
this response is common to all species of
fish and crustaceans and avoid transferring
animals to waters with higher pH.
This intolerance of catfish to abruptincreases in pH has important practicalconsiderations. Most newly hatchedcatfish fry are held for several daysin hatchery tanks supplied with flowthroughgroundwater with a pH near8.0. Fry are then transferred to a transporttank (usually filled with water fromthe same source used in the hatchery)and then stocked into a nursery pondfor further growth. Nursery pond pHcycles daily, and if fish are transferredto the nursery pond during the afternoonwhen pH is usually highest, manyfish may quickly die. The solution issimple: First measure the pH of thewater in both the transport tank and thepond, and then transfer fish only whenthe pH of the receiving water is verynear, or below, that of the transporttank water. Pond pH is usually lowest afew hours after dawn, so this is usuallythe best time to transfer fry.The physiological basis for the insensitivityof catfish fry to rapid increases inpH is unknown and a similar responsemay occur in other fish or crustaceanspecies. In the absence of additionalinformation farmers should assume thatthis response is common to all species offish and crustaceans and avoid transferringanimals to waters with higher pH.
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