Effect of nitrogen compounds on juvenile Pink Shrimp Camarão-Rosa Farfantepenaeus brasiliensis (Latreille, 1817) (Crustacea: Decapoda)
Aquaculture grows rapidly when compared to other sectors of animal food production. In Brazil, the consumption of shrimp from farms has grown a lot in recent years. Trying to diversify Brazilian shrimp production and reduce the environmental risks caused by the use of exotic species in coastal environments, the Marine Aquaculture Station of the Federal University of Rio Grande has been conducting studies to develop a technological production package for the native species Farfantepenaeus paulensis and F. brasiliensis in alternative systems in the Lagoa dos Patos estuary. This will make it possible to make better use of natural productivity in estuarine areas, enabling lower costs and allowing artisanal fishermen and small farmers to access a new source of income.The development and mastery of aquaculture techniques have caused intensification in the creation of different species, with a tendency to increase the generation of nitrogen compounds in these cultivation systems. Nitrogen compounds occur naturally in the aqueous medium, which can cause mortality or affect the growth of aquatic organisms. The most abundant nitrogenous forms in cultivation nurseries are ammonia, nitrite and nitrate. Ammonia is the end product of protein catabolism in most aquatic organisms. In the aqueous medium, ammonia is present in ionized and non-ionized form, with the sum of the two constituting total ammonia. The most toxic chemical form is non-ionized ammonia, due to its ability to diffuse through cell membranes,and also because the effect of ionized ammonia is less pronounced. Nitrite is the intermediate compound in the bacterial nitrification of ammonia to nitrate (in oxidizing media), or product of nitrate denitrification (in reducing environments). This can turn out to be quite toxic, according to its concentration in the environment and the stage of development in which the cultivated organisms are found, and can cause mortality in larvicultures and cultivation systems. Nitrate, being the final product of nitrification, can accumulate in large quantities, mainly in closed cultivation systems. This substance can cause lethal or sublethal effects for different organisms, or even act synergistically with other nitrogen compounds. From these statements,it is extremely important to study its toxic effects for the development of different species. For this, laboratory experiments were carried out in order to evaluate the effects of nitrogen compounds on juveniles of F. brasiliensis. The median lethal concentrations and safety levels of ammonia, nitrite and nitrate for the species were determined through short-term toxicity tests. Nitrogen products proved to be potentially toxic, in concentrations lower than the proposed safety level. Analyzing the growth and survival of juveniles exposed to nitrogen, the shrimp F. brasiliensis was susceptible to the compounds in concentrations equivalent to the levels of safety proposed for the species. For oxygen consumption,juveniles of pink shrimp exposed to nitrogen concentrations with 200% of the safety level expressed the highest consumption. In turn, the food consumption of juveniles of F. brasiliensis was influenced by the tested compounds (nitrite and nitrate).