Production rate (17/58 kg/ha per day) observed in this study could be
reasonably compared with production rate of most of the commercial systems (Chen
and Wang, 1990; Lumare et al., 1993). In the present study, shrimp production
increased significantly with the stocking density, this is in agreement with the report
of Allan and Maguire (1992).
Shrimp survival rate observed in the present study was lower than that reported by
Liao (1987); however, there was no significant difference in shrimp survival rates
among the treatments. This suggested that increasing stocking density up to 50
shrimp per m2 in closed system had not affected shrimp survival; and lower survival
rate observed in the present study as compared with the report of Liao (1987) could
be ascribed to any other reason rather over crowding. This contention is in
agreement with the observation of Allan and Maguire (1992) who reported that
increasing stocking densities from 5 to 40 shrimps/m2 had no effect on survival of P.
monodon. Moreover, in the present study the exceptionally low survival rate (35 and
38%) was observed in two tanks could not be related to any of the water quality
parameter measured. This is to mention here that TAN and NO2-N concentration in
those tanks remained relatively low (TANB/0.81 mg/l; NO2-NB/0.09), and therefore,
could not explain the low survival rate.
FCR value observed in this study could be reasonably compared with the previous
reports on P. monodon culture (Chen et al., 1989; Lumare et al., 1993). Sandifer et al.
(1991) reported that intensive shrimp ponds typically have a feed conversion ratio of
2.0 or above. The low FCR value obtained in this study may be ascribed to the strict
control of feeding by trays as well as the build up of benthic population over time
might have supported shrimp growth. This study showed the potential of closed
system in producing shrimp with low FCR, as in the closed system nutrient and
organic matter released to the system could be accounted well for the production of
natural food organisms. Reymond and Lagardere (1990) reported that in low
stocking density culture systems meiofauna may constitute an important part of the
feeding. Avnimelech et al. (1994) also emphasized that in ponds operated with high
water exchange rate, a large fraction of the feed and the organic matter accumulating
in the pond is drained and often wasted.