Cyclical fluctuations in ammonia and nitrite-nitrogen resulting from the feeding of turbot, scophthalmus maximus (L.), in recirculating systems

Daily and weekly cyclical fluctuations in ammonia (NH₄N µg litre^-1) and nitritenitrogen (NO₂N µg litre^-1) were shown to occur in marine recirculating systems containing juvenile turbot, Scophthalmus maximus (L.). A stepwise multivariant regression analysis, computed for the prefeeding morning base levels, showed that ammonianitrogen concentration in the fish tanks was related to inflow ammonianitrogen concentration, water flow rate, water temperature, mean fish weight and fish biomass. Influent ammonia concentration and water flow rate were by far the most important variables accounting for 68·0% and 16·7% of the variation in the regression respectively. The fluctuations, which occurred at concentrations thought to be tolerated by the fish, were attributed to the amount and timing of feeding. The significance of the existence of such fluctuations was discussed together with the importance of their amplitude and frequency. © 1987.