Effect of feed ration on ammonium accumulation and survival of Dormitator latifrons

Objectives. Evaluate experimentally the effect of the food ration on the accumulation of total ammonia nitrogen and the survival of D. latifrons. Materials and methods. A completely randomized experimental design was implemented, without water replacement for 72 h; using 10 fish per replicate and three replicates per treatment, feed rations of 2, 4, 6, and 8% in relation to biomass and balanced shrimp feed with 35% protein. Water quality variables and survival were recorded every 24 h. Results. Total ammonia varied between 1.05 and 7.80 mg*L-1, while non-ionized ammonium varied between 0.33 and 2.27 mg*L-1. Total ammoniacal nitrogen (5.16±1.70 mg*L-1) and non-ionized ammonium (1.56±0.48 mg*L-1) were significantly (p<0.05) higher in the 2% ration; however, this ration showed the highest survival (56–100%). Survival was reduced in all treatments; rations of 6 and 8% have recorded mortality since 24 h. The average lethal dose (LD50%) at 72 h was estimated with a food ration of 5.54% with respect to biomass. Conclusions. Dormitator latifrons resists concentrations of non-ionized ammonium above 1 mg*L-1. In intensive cultures of D. latifrons, a food ration less than 4% of biomass should be used, with water replacements at least every 48 h to avoid mortalities.