Association between trichodiniasis in eel (Anguilla anguilla) and water quality in recirculation systems
2000
Madsen, H.C.K. | Buchmann, K. | Mellergaard, S.
Association between various water quality parameters and the infection level of Trichodina jadranica in cultured eels were examined in nine recirculation farms in Denmark. Production units suffering from trichodiniasis (n = 4) had relatively high contents of organic dry matter (13-65 mg l-1), low concentrations of nitrate (150-500 mg NO3 l-1) and high pH (6.2-7.4) in the process water compared to farms without Trichodina problems (n = 5), which had a relatively low load of organic dry matter (9-16 mg l-1), high nitrate concentration (250-900 mg NO3 l-1) and a low pH (5.4-6.9). More detailed studies of the effect of water parameters on the infection level were conducted in two production units suffering from frequent outbreaks of trichodiniasis. In one production unit, the high and highly varying content of organic dry matter (21-83 mg l-1) was significantly and positively correlated (r = 0.37, p < 0.001) to the intensity of infection (1-150 trichodinids per fish) during a 19-day period. In the other production unit (with a low and stabile content of organic dry matter (2-7 mg l-1)), no correlation was seen neither between a high and highly varying concentration of nitrate (635-1104 mg NO3 l-1) and intensity of infection nor between a low and highly varying pH (5.45-6.39) and intensity of infection (2-300 trichodinids per fish) during a 17-day period. It is suggested that the infection pressure from trichodiniasis in farms with a relatively high load of organic dry matter (> 15-20 mg l-1) may be reduced by reducing the content of organic dry matter in the process water.
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