The influence of fish culture in floating net cages on microbial indicators of water quality

This work was carried out to analyse the microbiological parameters of the water quality of a reservoir used for the irrigation and culture of tilapia (Oreochromis niloticus) in floating net cages. The physico-chemical parameters, counts of mesophilic total aerobic bacteria, total and thermotolerant coliforms and fecal streptococci, and the presence of Escherichia coli in samples of water collected in three sites of the reservoir (pre-culture site, culture site, post-culture site) were analysed. The levels of ammonia (0.047-0.059 mg/L), nitrite (0.001-0.021 mg/L) and total phosphorus (0.050-0.355 mg/L) in the water did not show significant differences (p > 0.05) between sampling sites. The levels of total bacteria in the water varied between 1.3 x 104 and 67.3 x 104 CFU/100 mL. The MPN values of thermotolerant coliforms (< 930 MPN/100 mL) were within values recommended for water used for fish culture and/or irrigation. The presence of E. coli and fecal streptococci were verified in 48% and 56% of analysed samples, respectively. The site with floating net cages showed more samples contaminated with E. coli and fecal streptococci than other sampling points

The influence of fish culture in floating net cages on microbial indicators of water quality

This work was carried out to analyse the microbiological parameters of the water quality of a reservoir used for the irrigation and culture of tilapia (Oreochromis niloticus) in floating net cages. The physico-chemical parameters, counts of mesophilic total aerobic bacteria, total and thermotolerant coliforms and fecal streptococci, and the presence of Escherichia coli in samples of water collected in three sites of the reservoir (pre-culture site, culture site, post-culture site) were analysed. The levels of ammonia (0.047-0.059 mg/L), nitrite (0.001-0.021 mg/L) and total phosphorus (0.050-0.355 mg/L) in the water did not show significant differences (p > 0.05) between sampling sites. The levels of total bacteria in the water varied between 1.3 x 104 and 67.3 x 104 CFU/100 mL. The MPN values of thermotolerant coliforms (< 930 MPN/100 mL) were within values recommended for water used for fish culture and/or irrigation. The presence of E. coli and fecal streptococci were verified in 48% and 56% of analysed samples, respectively. The site with floating net cages showed more samples contaminated with E. coli and fecal streptococci than other sampling points

Response surface analysis on the effect of temperature and pH on Growth and proteolytic activity of thermophilic Bacillus sp

Proteolytic activity and cell biomass of thermophilic Bacillus sp. strain were evaluated at various levels of initial pH and temperature by applying response surface methodology. The mineral medium containing yeast extract (0.01%) and starch (1%) was used throughout the experiment. The results of statistical analysis revealed the polynomial model with high coefficient of determination (R² = 0.8) for the biomass and total proteolytic activity of the strain studied. This model showed a satisfactory adjustment of the statistic model with the experimental data. The p values showed that the temperature and pH had significant effect on biomass and proteolytic activity (P<0.05) of strain tested. The highest proteolytic activity (2.333 U/ml/h) of the Bacillus sp. was predicted at 41º C and pH 4.8. The high biomass values were observed at broad range of temperature and pH.<br>Atividade proteolítica total e biomassa de uma linhagem de Bacillus sp. termofílico foram analisados em vários níveis de pH inicial e temperatura utilizando a metodologia de superfície de resposta. O meio mineral com extrato de levedura (0.01%) e amido (1%) foi utilizado no experimento. Os resultados de análise estatística da metodologia de resposta de superfície definiram um modelo polinomial para a biomassa e atividade proteolítica da linhagem de Bacillus sp. com alto coeficiente de determinação (R² = 0.8), mostrando um ajuste satisfatório do modelo estatístico obtido com os dados experimentais. Os valores de p mostraram que a temperatura e pH tiveram efeito significante em biomassa e atividade total (P <0.05) da linhagem testada. A atividade proteolítica mais alta (2.368 U/ml/h) da linhagem de Bacilus sp. foi prevista pelas curvas de superfície de resposta em temperatura a 41º C e pH igual a 4.8. Os valores de biomassa altos foram previstos para ampla faixa de temperatura e pH