L. Vannamei Case Study

2.6.6. Levels of total ammonia nitrogen, nitrite, nitrate and phosphate in the water samples The mean TAN levels in the present study in all the sampling stations were below the recommended level of 0.1 to 1.0 mg/L prescribed by Boyd (1990). However, when the level recommended (< 0.2 mg/L) by Chavez (2009) is taken as a standard, it was found to that 35% of the study period, TAN levels were above the acceptable limit in the feeder canal and the pond 3. Ferreira et al. (2011) has recommended 0.2 mg/L as the acceptable level of TAN for the culturing of L. vannamei. Though the mean TAN levels of the sampling sites were within this limit, the TAN levels went above the recommended level often in all the sampling stations showing that both the source water and the water of shrimp ponds were not suitable for the culturing of L. vannamei. It is a well documented fact that the
vannamei. The range of phosphate levels seen in the feeder canal and shrimp ponds of the present study were much higher than that recorded by Sahu et al. (2013) in P. monodon culture ponds of eastern India. Phosphorous a nutritive element occurs as orthophosphate in water and is essential for aquatic life (Esteves, 1998; Ferreira et al., 2011). Rise in salinity increases the release of phosphate into the water column (Pereira Cardozo et al., 2011; Gireeshkumar et al., 2013). In water, inorganic phosphate levels are dependent on both external sources and also from the release of trapped in sediments (García and de Iorio 2003). Nitrate and phosphate demonstrated an insignificant negative correlation was salinity in the feeder canal and Pond 4 and a similar observation was recorded by Martin et al. (2008) in the Cochin estuary. In other sites (Ponds 1, 2 and 3), salinity showed an insignificant inverse relationship with