pH value of the rearing water was also used as a water quality criterion
in 41 trials, and the minimum pH ranged between 7.54 and 8.03.
The larval hatching date ranged from 28 April to 18 September. The
numbers of larvae stocked in the seed production tankswere calculated
based on the brood weights of ovigerous females, according to the
equation proposed by Hamasaki (1996). The stocking density was
7800–69,400 larvae kL−1 (n = 111; average = 28,000 kL−1). The
number of surviving larvaewas estimated using the volumetric method
until themegalopal stage, according to themethod described by Kogane
et al. (2007). The larvae moulted during the night, and the surviving
larvae were counted on the next day after moulting. Counts were
made during the hour after dusk in the fourth zoeal and megalopal
stages, because the larvae were not distributed homogeneously in the
tank during the day-time. The juvenile crabs were harvested mainly at
the first crab stage, although 40.3% of the trials included second stage
crabs. The number of harvested crabs was estimated using a weighing
methodwhereby the total harvestedweightwas converted to the number
of crabs based on the average number of crabs per unit weight,
which was counted in small samples of harvested crabs during each
trial. The number of newly hatched larvae and harvested juvenile
crabs was estimated in all trials. The numbers of surviving larvae at all
larval stages were estimated based on 52 trials (26 trials each year during
2009 and 2010) conducted in six hatcheries, and the numbers of
surviving fourth-stage zoeae and megalopae were estimated based on
58 trials (31 and 27 trials during 2009 and 2010, respectively)
conducted in eight hatcheries.
pH value of the rearing water was also used as a water quality criterion
in 41 trials, and the minimum pH ranged between 7.54 and 8.03.
The larval hatching date ranged from 28 April to 18 September. The
numbers of larvae stocked in the seed production tankswere calculated
based on the brood weights of ovigerous females, according to the
equation proposed by Hamasaki (1996). The stocking density was
7800–69,400 larvae kL−1 (n = 111; average = 28,000 kL−1). The
number of surviving larvaewas estimated using the volumetric method
until themegalopal stage, according to themethod described by Kogane
et al. (2007). The larvae moulted during the night, and the surviving
larvae were counted on the next day after moulting. Counts were
made during the hour after dusk in the fourth zoeal and megalopal
stages, because the larvae were not distributed homogeneously in the
tank during the day-time. The juvenile crabs were harvested mainly at
the first crab stage, although 40.3% of the trials included second stage
crabs. The number of harvested crabs was estimated using a weighing
methodwhereby the total harvestedweightwas converted to the number
of crabs based on the average number of crabs per unit weight,
which was counted in small samples of harvested crabs during each
trial. The number of newly hatched larvae and harvested juvenile
crabs was estimated in all trials. The numbers of surviving larvae at all
larval stages were estimated based on 52 trials (26 trials each year during
2009 and 2010) conducted in six hatcheries, and the numbers of
surviving fourth-stage zoeae and megalopae were estimated based on
58 trials (31 and 27 trials during 2009 and 2010, respectively)
conducted in eight hatcheries.
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