Nitrite concentrationsfluctuatedamong the different farms (Table 3).
Mortality associatedwith elevated nitrite concentrationwas observed in
only one case, where the concentration reached 40 mg/l during a short
period (www.danskakvakultur.dk) probably due to impaired biofilter
activity (Svobodova et al., 2005). Ammonia concentrations were kept
below 0.025 mg/l in all 8 farms. Consequently, no fish mortality was
ascribed to ammonia poisoning.