Use of eggshell as an alternative substrate for biofilters in recirculation aquaculture systems

One of the biggest challenges of recirculating systems (RAS) is keeping levels of toxic compounds, such as ammonia, low. This work sought to evaluate the use of eggshell as a biofilter substrate in the cultivation of juvenile Oreochromis niloticus. The experiment lasted 90 days, using four treatments: A) 100% expanded clay, A+CO) 50% expanded clay and 50% eggshell, PC) MBBR3 and NC) without substrate, with three replications each, storing 15 juveniles with an initial weight of 1.26±0.08g. Feeding occurred three times a day with commercial food offered until apparent satiety. The following parameters were monitored: pH, temperature (ºC), dissolved oxygen (mg L-1), electrical conductivity (µS cm-1) and total soluble solids (ppm); and zootechnical performance indices: survival rate (%), weight gain (g), specific growth rate (% day-1) and condition factor. Water samples were collected at the inlet and outlet of the biofilters on days 0, 30 and 60 of the experiment. Means were compared using the 5% Tukey test. All biofilters used maintained water quality parameters within those recommended for production, with emphasis on A+CO. The concentrations of ammonia at the inlet of the A+CO biofilter were lower than the others, providing lower levels of this substance in the system and high concentrations of nitrate. It was concluded that the biofilter composed of 50% expanded clay and 50% eggshell showed better efficiency in maintaining water quality compared to the others, revealing its potential as an alternative biological substrate.