Ammonia toxicity as a criterion for the evaluation of larval quality in the prawn Macrobrachium rosenbergii

The feasibility of a short-term ammonia toxicity test as an evaluation crit erion for larval quality was assessed in three trials. In each one, Macrobr achium rosenbergii larvae originating from the same spawn were nutritionall y differentiated in two groups by feeding them either a nutrient-rich (Arte mia nauplii enriched for 24 h with n-3 highly unsaturated fatty acids (HUFA ) and ascorbic acid (AA)) or a nutrient-poor diet (Artemia nauplii starved for 24 h). Throughout their development. larvae from both treatments were e xposed during 24 h to six concentrations of total ammonia (NH4+ + NH,) and a control (no ammonia added). Based on mortality rates, the median lethal c oncentration for 50% of the population (LC50) was estimated. As expected fr om earlier work, larvae fed the optimal diet presented higher n-3 HUFA and AA contents as well as higher growth and metamorphosis rates. From the mome nt the effect of diet quality was analytically detectable in the tissues of the larvae, the ammonia test was able to distinguish both groups of larvae . Differences in ammonia tolerance were observed as early as larval stage 4 and remained evident throughout larval development. The short-term ammonia toxicity test proved to be a valuable, sensitive and reproducible criterio n for the establishment of larval quality. (C) 2000 Elsevier Science Inc. A ll rights reserved.