decomposition. High ammonia concentrations in larviculture tanks can result in mortality and poor performance even at sub lethal levels.
Different species are known to vary greatly in their tolerance to ammonia. Therefore, knowledge of the ammonia tolerance levels of candidate species is important for the culturist in order to optimize survival. The effect of ammonia on larvae was evaluated to provide basic information on safe levels for larviculture of M. vollenhovenii.
A 96 h static assay was performed on 1 day old M. vollenhovenii larvae. The nominal concentrations tested ranged from 2 to 16 mg NH4/L (0, 2, 4, 8 and 16 mg/L) with three replicate beakers per treatment dose. Water temperature was maintained at 26circC by use of a single water bath and a submersible heater. The salinity of the test water was adjusted to 16 ppt using a commercially available marine mix (Crystal Sea™, Baltimore, MD).
Ten one-day-old prawn larvae were individually counted into each of eighteen 200 ml glass beakers containing 200 ml of preconditioned water. Test concentrations of ammonia were obtained by first making a test solution of reagent grade ammonium chloride (NH4Cl) and then applying by pipette from the solution to the individual beakers.
Mortalities were observed under a magnifying glass and recorded every 24 hours. Ammonia concentrations were measured using a spectrophotometer to test accuracy of serial dilutions. Data were analyzed using Probit Analysis EPA edition.
There was no mortality in control treatments during the experiment. Neither was observed any mortality during the first 24 hours of exposure for all ammonia concentrations. After 96 h, all larvae exposed to the highest concentration tested (16 mg/L) died. The 96 h LC50 value was calculated to be 7.4 mg/L (Figure 1).
These results suggest that M. vollenhovenii exhibits a lower tolerance to ammonia when compared to other species of freshwater prawn including: Macrobrachium