RESUMO
Nitrogen compounds, particularly ammonium, nitrite and nitrate, are a major problem in shrimp production systems. These compounds can accumulate in the aquatic environment and reach harmful or even lethal levels. Thus, monitoring the levels of nitrogenous compounds such as ammonia and studying their effects on the animals are essential. One tool used for this purpose is acute toxicity testing based on the evaluation of LC50 values. Furthermore, tools that can help improve the performance of aquatic organisms in culture are needed. The present study aimed to evaluate the effect of salinity on the toxicity of total ammonia to postlarvae of the freshwater prawn Macrobrachium rosenbergii. For this purpose, acute toxicity testing (LC50-96h) was performed using 540 postlarvae with a mean weight of 0.13 g and a mean total length of 2.47 cm, divided into 54 experimental units of two liters each. A completely randomized design in a 3×6 factorial scheme was used, combining three salinities (0, 5, and 10 g.L-1) and six total ammonia concentrations (0, 8, 16, 32, 64, and 128 mg.L-1), with three replicates per combination. The LC50 values for M. rosenbergii postlarvae at 24, 48, 72, and 96 h and their respective confidence intervals (95%) were estimated using the trimmed Spearman-Karber method. The results showed that salinities of 5 or 10 g.L-1 did not reduce the acute toxicity of total ammonia.
Assuntos
Amônia , Palaemonidae , Animais , Amônia/toxicidade , Salinidade , Nitritos , NitratosRESUMO
Adapting existing laying facilities to meet animal welfare certifications is not a simple task. It causes higher expenses to producers, who are often hesitant to accept the need for changes. Considerations of their financial situation make them insecure to make assertive decisions in this area, as they seek to maintain the economic efficiency of laying poultry. This study aims to analyze the economic viability of laying systems (conventional cages and Cage-Free) with different housing densities. The data source was a systematized literature review. Five articles were found containing reports on systems. Further data sources were the lineage handbook and a survey with companies specializing in poultry farming. An analysis of economic viability was performed in the multiple scenarios. Densities in each system were used to compose different scenarios: Conventional: 1,500 cm²/bird, 750 cm²/bird, and 398 cm²/bird; and Cage-Free:7 birds/m² and 13 birds/m². The scenarios were evaluated in terms of Net Present Value, Internal Rate of Return, Modified Internal Rate of Return, Discounted Payback Method, Profitability Index, Equivalent Uniform Annual Value, and Monte Carlo Simulation. The best scenario was the Conventional, with 398 cm²/bird, presenting a higher NPV. The Cage-Free system, with seven birds per square meter, had a lower NPV compared to conventional systems. All scenarios had satisfactory chances of success. The risks of negative or null financial return were low according to Monte Carlo simulations. Conventional and Cage-Free production are economically viable when using densities of 1,500 cm²/bird, 750 cm²/bird, or 398 cm²/bird (conventional), and 7 birds/m², or 13 birds/m² (Cage-Free).(AU)