Relevância da alcalinidade, pH e dióxido de carbono na sobrevivência e crescimento de Litopenaeus vannamei (Boone 1931) em sistema de bioflocos
Resumo
Os cultivos de organismos aquáticos em sistemas sem renovação de água que utilizam altas densidades de estocagem, forte aeração e biota predominantemente aeróbia e heterotrófica, formadora de flocos microbianos são chamados de tecnologia de bioflocos (BFT). Estes sistemas são considerados biosseguros e permitem elevar a produtividade do cultivo devido ao suplemento nutricional fornecido pelos bioflocos. Como não há renovação de água ao longo do cultivo e a água pode ser reutilizada por vários ciclos de produção, ocorre a redução dos níveis de alcalinidade e de pH , podendo também ocorrer um acúmulo de dióxido de carbono (CO2), proveniente dos processos respiratórios dos camarões e dos bioflocos. Alterações na qualidade de água de cultivo geram estresse e reduzem o crescimento e a capacidade de resposta do sistema imunológico, podendo afetar a sobrevivência dos camarões. Este trabalho busca aprimorar as técnicas de cultivo de Litopenaeus vannamei em sistemas de bioflocos sem renovação de água, compreendendo e corrigindo as concentrações de dióxido de carbono, alcalinidade e pH. Para tal, foram realizados cinco experimentos na estação marinha de aquacultura da Universidade Federal do Rio Grande (EMA-FURG-Brasil) e um na Universidad Nacional Autónoma do México (UMDI-Sisal-UNAM): 1. Determinação do nível letal do pH ácido e básico (pH50-96h) e avaliação do efeito subletal do pH nos parâmetros de estresse oxidativo em juvenis de L. vannamei; 2. Determinação da concentração letal e do nível de segurança de dióxido de carbono para juvenis de L. vannamei; 3. Verificação das concentrações de CO2 em diferentes densidades de cultivo e de sólidos em suspensão quando ocorre falha no sistema de aeração e se aplica peróxido de hidrogênio (H2O2) como fonte de oxigênio em sistema BFT; 4. Avaliação do efeito do CO2 no consumo de oxigênio de juvenis de L. vannamei cultivados em sistema BFT; 5. Avaliação do efeito de diferentes concentrações de alcalinidade nos parâmetros de qualidade da água, na formação dos bioflocos e no desempenho zootécnico de L. vannamei cultivados em sistema BFT; 6. Determinação da melhor dosagem de hidróxido de cálcio (Ca(OH)2) nos parâmetros de qualidade da água e desempenho zootécnico de L. vannamei cultivados em sistema BFT. Nas condições experimentais descritas no capítulo 1, o pH50 96 h de pH ácido e básico foram de 4,04 e 9,58 para juvenis de L. vannamei. Quanto ao ensaio de estresse oxidativo constatamos que os camarões expostos tanto ao pH 4,5 como ao pH 9,5 apresentaram desequilíbrio na atividade das enzimas antioxidantes. Já no Capítulo 2 encontramos os valores de CL50 e limites de confiança 95% em 24, 48, 72 e 96 h foram de 130,05 (104,2-162,1), 77,2 (73,8-80,02), 69,65 (65,47-74,32), 59,12 (53,08-66,07) mg/L de CO2, respectivamente. Assim, o nível de segurança calculado para L. vannamei foi de 5,9 mg/L de CO2. No capítulo 3 verificamos que as concentrações de CO2 se incrementaram com os incrementos de biomassa e de sólidos suspensos totais com o passar do tempo, alcançando valores subletais de CO2 para os camarões. No capitulo 4 foi verificado um incremento no consumo de oxigênio de juvenis nas concentrações de até 60 mgCO2/L e uma redução no consumo de oxigênio nas concentrações de 95, 150 e 300 mgCO2/L seguido de sintomas de anestesia e mortalidade. No Capítulo 5 foi possível formar bioflocos com valores de alcalinidade superiores a 70 mgCaCO3/L e pH superior a 7,38. Contudo, as melhores taxas de nitrificação e melhor desempenho zootécnico ocorreram nos tratamentos com maior alcalinidade. No capítulo 6 para a correção da alcalinidade, pH e CO2 pode ser aplicado dosagens de 0,05 g/L de hidróxido de cálcio ou aplicações diárias entre 10 e 20% da quantidade de ração ofertada aos camarões. Os resultados obtidos poderão auxiliar no dia a dia dos produtores de camarões em sistemas BFT.
The Biofloc technology (BFT) is the system of production of aquatic organisms in high stocking densities without water renewal, using strong aeration and predominantly aerobic and heterotrophic biota that form microbial flakes. These systems are considered biosafe and raise cultivation productivity due to the nutritional supplement provided by the bioflocs. As there is no renewal of water along the cultivation and the water can be reused for several cycles of production, the levels of alkalinity and pH are reduced and carbon dioxide (CO2) derived from the respiration of shrimp and bioflocs can be accumulated. Changes in the quality of cultivation water can generate stress and reduce immune system responses and the growth and survival of the shrimp. Thus, this study aimed to improve cultivation techniques of Litopenaeus vannamei in biofloc systems without water renewal by means of comprehension and correction of carbon dioxide, alkalinity and pH levels. To this end, five experiments were performed at the Marine Aquaculture Station, Federal University of Rio Grande (EMA - FURG - Brazil) and one experiment was performed at the National Autonomous University of Mexico (UMDI-Sisal-UNAM): 1. Determination of the lethal concentration of acid and basic pH (pH50-96h) and assessment of the sublethal effect of the pH on oxidative stress parameters in juveniles of L. vannamei; 2. Determination of the lethal concentration and the safety level of carbon dioxide for juveniles of L. vannamei; 3. Verification of the CO2 concentrations and suspended solids at different stocking densities when there is a failure in the aeration system and hydrogen peroxide (H2O2) is applied as a source of oxygen in the BFT system; 4. Evaluation of the effect of CO2 in the oxygen consumption of L. vannamei juveniles reared in the BFT system; 5. Evaluation of the effect of different levels of alkalinity in the parameters of water quality, in the formation of bioflocs and in the zootechnical performance of L. vannamei reared in the BFT system; 6. Determination of the optimum dosage of calcium hydroxide (Ca(OH)2) in the parameters of water quality and growth performance of L. vannamei cultivated in the BFT system. Under the experimental conditions described in Chapter 1, the pH50 96 h results of acid and basic pH for L. vannamei juveniles were 4.04 and 9.58. As for the oxidative stress test, we found out that the shrimp exposed to both pH 4.5 and pH 9.5 presented an imbalance in the activity of antioxidant enzymes. In Chapter 2, LC50 values with 95% confidence limits in 24, 48, 72 and 96 h were 130.05 (104.2-162.1), 77.2 (73.8-80.02), 69.65 (65.47-74.32), 59.12 (53.08-66.07) mg/L of CO2, respectively. Thus, the calculated safety level for L. vannamei was 5.9 mg/L of CO2. In Chapter 3 we noted that CO2 levels increased with the increments of biomass and total suspended solids over time, reaching sublethal levels of CO2 for the shrimp. In Chapter 4 an increase in oxygen consumption of immature fish was observed at concentrations up to 60 mgCO2/L and a reduction in the oxygen consumption at the concentrations of 95, 150 and 300 mgCO2/L, followed by anesthesia symptoms and mortality. In Chapter 5 bioflocs were formed in alkalinity and pH levels greater than 70 mgCaCO3/L and 7.38, respectively. However, the best rates of nitrification and zootechnical performance occurred in the treatment with the highest levels of alkalinity. In Chapter 6, 0.05 g/L of calcium hydroxide or daily doses of 10 and 20% of the amount of feed offered to the shrimp were applied to correct the alkalinity, pH and CO2. The results obtained could assist the daily routine of shrimp farmers using BFT systems.
The Biofloc technology (BFT) is the system of production of aquatic organisms in high stocking densities without water renewal, using strong aeration and predominantly aerobic and heterotrophic biota that form microbial flakes. These systems are considered biosafe and raise cultivation productivity due to the nutritional supplement provided by the bioflocs. As there is no renewal of water along the cultivation and the water can be reused for several cycles of production, the levels of alkalinity and pH are reduced and carbon dioxide (CO2) derived from the respiration of shrimp and bioflocs can be accumulated. Changes in the quality of cultivation water can generate stress and reduce immune system responses and the growth and survival of the shrimp. Thus, this study aimed to improve cultivation techniques of Litopenaeus vannamei in biofloc systems without water renewal by means of comprehension and correction of carbon dioxide, alkalinity and pH levels. To this end, five experiments were performed at the Marine Aquaculture Station, Federal University of Rio Grande (EMA - FURG - Brazil) and one experiment was performed at the National Autonomous University of Mexico (UMDI-Sisal-UNAM): 1. Determination of the lethal concentration of acid and basic pH (pH50-96h) and assessment of the sublethal effect of the pH on oxidative stress parameters in juveniles of L. vannamei; 2. Determination of the lethal concentration and the safety level of carbon dioxide for juveniles of L. vannamei; 3. Verification of the CO2 concentrations and suspended solids at different stocking densities when there is a failure in the aeration system and hydrogen peroxide (H2O2) is applied as a source of oxygen in the BFT system; 4. Evaluation of the effect of CO2 in the oxygen consumption of L. vannamei juveniles reared in the BFT system; 5. Evaluation of the effect of different levels of alkalinity in the parameters of water quality, in the formation of bioflocs and in the zootechnical performance of L. vannamei reared in the BFT system; 6. Determination of the optimum dosage of calcium hydroxide (Ca(OH)2) in the parameters of water quality and growth performance of L. vannamei cultivated in the BFT system. Under the experimental conditions described in Chapter 1, the pH50 96 h results of acid and basic pH for L. vannamei juveniles were 4.04 and 9.58. As for the oxidative stress test, we found out that the shrimp exposed to both pH 4.5 and pH 9.5 presented an imbalance in the activity of antioxidant enzymes. In Chapter 2, LC50 values with 95% confidence limits in 24, 48, 72 and 96 h were 130.05 (104.2-162.1), 77.2 (73.8-80.02), 69.65 (65.47-74.32), 59.12 (53.08-66.07) mg/L of CO2, respectively. Thus, the calculated safety level for L. vannamei was 5.9 mg/L of CO2. In Chapter 3 we noted that CO2 levels increased with the increments of biomass and total suspended solids over time, reaching sublethal levels of CO2 for the shrimp. In Chapter 4 an increase in oxygen consumption of immature fish was observed at concentrations up to 60 mgCO2/L and a reduction in the oxygen consumption at the concentrations of 95, 150 and 300 mgCO2/L, followed by anesthesia symptoms and mortality. In Chapter 5 bioflocs were formed in alkalinity and pH levels greater than 70 mgCaCO3/L and 7.38, respectively. However, the best rates of nitrification and zootechnical performance occurred in the treatment with the highest levels of alkalinity. In Chapter 6, 0.05 g/L of calcium hydroxide or daily doses of 10 and 20% of the amount of feed offered to the shrimp were applied to correct the alkalinity, pH and CO2. The results obtained could assist the daily routine of shrimp farmers using BFT systems.
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Citação
FURTADO, Plinio Schmidt. Relevância da alcalinidade, pH e dióxido de carbono na sobrevivência e crescimento de Litopenaeus vannamei (Boone 1931) em sistema de bioflocos. 2014. 167 f. Tese (doutorado) - Programa de Pós-Graduação em Aquicultura, Instituto de Oceanografia, Universidade Federal do Rio Grande, Rio Grande, 2014.