Biblioteca Central de la Universidad Nacional del Santa

ABSTRACT Evaluated the variation of the concentration of total ammoniacal nitrogen (NAT) in two recirculation systems of water with crops of Oreochromis niloticus "nilotica tilapia" in laboratory. Were installed two water recirculation systems to 100%, one with biofiltro (experimental treatment) and the other without biofiltro (treatment control); each system consisted of three aquariums in 100 liters of capacity, which were filled by vessels communicating together one with another, using as a lifting force atmospheric pressure, gravity and difference of levels. In the first aquarium of both treatments were placed 60 juveniles of "nilotica tilapia" of 4,8 ± 0,1 g of average weight, which were fed to satiety; a solids separator was installed in the second aquarium of the experimental treatment and a thermostat was placed on both treatments and third experimental treatment aquarium installed a biofiltro and in both treatments a degasifier (broadcasters stones). The study lasted two weeks, registering quality parameters of water as oxygen (mg l-1), temperature (°C), pH, concentration of total ammoniacal nitrogen (NAT) (mg l-1), ammonia (mg l-1) and nitrate (NO3 mg l-1), which were measured three times a day (9:00 am, 12:00 and 18:00 hours) at the output of the aquarium water where they were fish and in the degasifier. It was concluded that there is significant difference (p < 0,05) between the experimental treatment, where the toxic metabolites excreted by fish (NAT, NH3-N) maintained low levels (0,05 and 0,001 mg l-1); with regard to the treatment control where levels were increased (3,70 and 0,007 mg l-1). Key words: Oreochromis niloticus, water recirculation systems, concentration of total ammoniacal nitrogen.