Toxidade aguda e crônica por amônia do camarão de água-doce Macrobrachium amazonicum, Heller, 1862

Abstract

Water quality is essential for the success of the aquaculture activity. In the case of freshwater shrimp farming, ammonia concentrations can increase considerably, even when the growing water is frequently renewed, increasing the risk of poisoning by this nitrogenous compound. Macrobrachium amazonicum has a relevant importance in ecology, in the chain, being widely fished and consumed in the Northeast region, this species has been used as a biomarker of the quality of water bodies and as a model organism for physiological, biochemical and molecular studies among the which we can mention: the evaluation of the effect of different salinities on larval survival and molting, the role of amino acids and salinity tolerance at different ontogenetic stages, the kinetic characterization of the (Na+ , K+ )-ATPase activity in adults and in different ontogenetic stages, the kinetic characterization of the K+ -phosphatase activity of (Na+ , K + )-ATPase under different salinity conditions, the ultrastructural characterization of the gills, the effect of medium salinity on the activity and expression of (Na+ , K+ )-ATPase and V(H+ )-ATPase, the effects of the presence of ammonia in the medium on different transporters and oxidative stress enzymes, the kinetic characterization of V(H+ )-ATPase activity at different ontogenetic stages, regulation of (Na+ , K+ )-ATPase activity by exogenous biogenic amines (Lucena et al., and regulation of (Na+ , K+ )-ATPase phosphorylation/dephosphorylation by exogenous biogenic amines. We investigated the ammonia lethality (LC50-96 h) in a hololimnetic population of the shrimp Macrobrachium amazonicum from the Paraná River / Paraguay Basin and the effects of a 'safe' ammonia concentration on the (Na+ , K+ )-ATPase activity of the gill. The mean lethal ammonia concentration during 96 h of exposure for this population was estimated to be 49.27 mg L-1 of total ammonia or 1.8 mg L-1 of non-ionized ammonia. This value is higher than that of populations from the Amazon River Basin and of M. rosenbergii and is comparable to those of marine crustaceans. The 'safe' level was calculated as 4.9 mg L -1 of total ammonia. Exposure of M. amazonicum to safe concentrations of ammonia (4.9 mg L-1 of total ammonia) for 10 days increased the activity of gill enzymes such as (Na+ , K + )-ATPase (1.3 times), V (H+ )-ATPase (2.5 times) and K+ -ATPase (2.5 times); these are the main enzymes that participate in the active excretion of ammonia. Western blotting of freshly captured gill microsomal homogenates from freshly captured shrimp showed a single immunoreactive band of ≈120 kDa, corresponding to the (Na+ , K+ )-ATPase α subunit. Shrimp exposed to ammonia also exhibited a weak diffuse band of ≈130 kDa. The affinity of gill (Na+ , K + )-ATPase for all modulators except NH4+ was not changed after exposure to ammonia; for NH4+ , the affinity increased 2.5 times in shrimp exposed to ammonia. Site-site interactions were observed for all modulators, except ATP, in freshly caught shrimp and exposed to ammonia. Although exposure to ammonia for 10 days did not cause mortality, lethargy or other manifestations, further studies are needed to establish the maximum acceptable toxic concentration of M. amazonicum ammonia for aquaculture purposes.