Milkfish Production and Processing ... - WorldFish Center

get overgrazed; gradually increase the
water level to 75-100 cm.
f) Apply inorganic fertilizer (18-46-0
or16- 0-0) at 50 kg/ha divided in small
doses every 1 -15 days. Application
of fertilizer is done either by directly
broadcasting the fertilizer to the water
or placing the fertilizer on a submerged
platform placed 1 to 0 cm below the
surface. Planktons should bloom after
a few days which are characterized by
a rich green water.
g) Closely monitor plankton growth
and adjust fertilizer dosage and frequency
of application to keep secchi
disk reading between 0 and 0 cm.
Reapply fertilizer if plankton does not
bloom but if secchi reading is less than
0 cm stop fertilization and replace
about ¼ of volume of pond water.
A combination of regular water
exchange and fertilization will maintain
good plankton blooms. Water
transparency of less than 0 cm
indicates plankton over bloom and
leads to plankton die-offs. Plankton
die-offs reduce dissolved oxygen of
pond water.
h) Supplemental feeds such as commercial
fish feed, rice brand or bread crumbs
should be supplied if the plankton
prematurely collapsed due to poor
water condition or persistent inclement
weather.
i) Start harvest when natural food in
the rearing pond becomes in short
supply and/or the target size of 00g
to 50g is attained.
j) Harvest when fish are scarce in the
market to maximize profit. This is
usually during full moon nights when
not much fish are caught in the sea.
18.4 Stock Manipulation or
Multi-Size Group Method
The stock manipulation method aims to maintain
a balance between the fish population and
natural food supply by periodic stocking of
multi-size fish and partial harvesting. Under
this technique of periodic stocking and partial
Milkfish Production and Processing Technologies in the Philippines
harvesting, fish biomass in the pond fluctuates
between 50 kg/ha to a maximum of 750 kg/ha
until each harvest. The carrying capacity of
brackishwater pond is from 700 to 800 kg /ha.
Annual fish yield using this method is ,000
to ,000 kg/ha. This method was developed
and popularly practiced in Taiwan. The steps
involved are as follows:
a) Follow water and fertilization management
as well as care of stock in
the nursery and transition ponds as
outlined in Sections 1 , 14, 15).
b) Stock milkfish fingerlings of assorted
sizes (5 to 100g) at 4,000-5,000 per
hectare in the grow-out pond preferably
during the month of April.
c) Acclimate the fish to pond environment
before stocking:
• If salinity and temperature of transport
containers and nursery pond
are approximately the same, stock
the fish directly.
• If not let the transport containers
float in the nursery pond for 15 to
0 minutes to equalize the temperature
of the containers with the
pond water.
• If salinity difference between transport
containers and nursery pond
is above 5ppt, gradually add pond
water to transport containers until
salinity is equalized before releasing
the fish.
• Allow the fry to swim out of the
containers.
d) If the fingerlings come from the farm,
use “pasulang” or freshening method
in transferring fish from one compartment
to another rearing compartment
to minimize stress. Follow transfer
procedures stated in Extensive Method
(Section A. 7. ).
e) Stock milkfish fry at 5,000 to 8,000
per hectare from May to August.
f) Provide rice bran as supplemental
feed at 0 to 50 kg/ha daily or every
two days to avoid overgrazing of
natural food.
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