Total nitrogen and total phosphorus concentration in water increased with the
progress of rearing. Throughout the study, soluble reactive phosphorus concentration
remained much lower than total phosphorous concentration, suggesting that a
large portion of water phosphorus was contained in suspended solids as well. In
addition, SRP concentration remained high throughout the rearing, the highest
concentration observed was 1100 mg/l. The result is in contrast to the report of Boyd
(1990) who mentioned that dissolved orthophosphate concentration are usually not
greater than 5/20 mg/l, and seldom exceed 100 mg/l even in highly eutrophic water. In
the present study water nutrient concentration was linearly correlated with the
cumulative feed input (data not shown). Obviously, being a closed system nutrient
kept on accumulating within the system over time; this might be an advantage of the
closed system as the high nitrogen and phosphorus accumulated within the system
could support the growth of natural food organisms contributing ultimately to the
shrimp growth. This view is in agreement with the report of Allan et al. (1995) who
observed that prawn grow faster in prepared ponds where meiofauna is abundant.
Chlorophyll-a concentration increased with the progress of rearing, and at the end
of the study chlorophyll-a reached as high as 808 mg/l which was higher than the
range reported previously for shrimp ponds (Lin, 1986; Martin et al., 1998).
Moreover, in the present study, chlorophyll-a concentration remained relatively high
(/94 mg/l) in all the treatments from fourth week of the rearing till the end of the
study, indicating that the system never became nutrient limiting, and thus, in turn,
sustained high phytoplankton biomass. Seemingly, dissolve nutrients together with
the high light intensity, and warm temperature supported active growth of
phytoplankton; which helped to condition the water quality in the tank by the
production of oxygen and uptake of dissolved nutrients (Krom and Neori, 1989).
Total nitrogen and total phosphorus concentration in water increased with theprogress of rearing. Throughout the study, soluble reactive phosphorus concentrationremained much lower than total phosphorous concentration, suggesting that alarge portion of water phosphorus was contained in suspended solids as well. Inaddition, SRP concentration remained high throughout the rearing, the highestconcentration observed was 1100 mg/l. The result is in contrast to the report of Boyd(1990) who mentioned that dissolved orthophosphate concentration are usually notgreater than 5/20 mg/l, and seldom exceed 100 mg/l even in highly eutrophic water. Inthe present study water nutrient concentration was linearly correlated with thecumulative feed input (data not shown). Obviously, being a closed system nutrientkept on accumulating within the system over time; this might be an advantage of theclosed system as the high nitrogen and phosphorus accumulated within the systemcould support the growth of natural food organisms contributing ultimately to theshrimp growth. This view is in agreement with the report of Allan et al. (1995) whoobserved that prawn grow faster in prepared ponds where meiofauna is abundant.Chlorophyll-a concentration increased with the progress of rearing, and at the endof the study chlorophyll-a reached as high as 808 mg/l which was higher than therange reported previously for shrimp ponds (Lin, 1986; Martin et al., 1998).Moreover, in the present study, chlorophyll-a concentration remained relatively high(/94 mg/l) in all the treatments from fourth week of the rearing till the end of thestudy, indicating that the system never became nutrient limiting, and thus, in turn,sustained high phytoplankton biomass. Seemingly, dissolve nutrients together withthe high light intensity, and warm temperature supported active growth ofphytoplankton; which helped to condition the water quality in the tank by theproduction of oxygen and uptake of dissolved nutrients (Krom and Neori, 1989).
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