Abstract

This study assessed the effects of three levels of water exchange during the start-up of recirculating aquaculture systems (RAS) on the growth and protein productive value (PPV) of pikeperch (Sander lucioperca) and on water quality parameters. The experiment was conducted in twelve independent RAS stocked with pikeperch (average body weight 247.4 g). The start-up phase of the RAS was described via the accumulating feed burden (AFB). Different water exchange levels were tested in quadruplicates as low AFB (final AFB of 1000 mg L−1 achieved through a water exchange of 1000 L per kg feed), medium AFB (final AFB of 1958 mg L−1 achieved through a water exchange of 500 L per kg feed) and high AFB (final AFB of 4422 mg L−1 achieved through a water exchange of 200 L per kg feed). Fish were fed daily at 0.9% biomass (BM) with a commercial diet (ALLER Metabolica) and individual body weight was assessed after 14, 35 and 56 feeding days. Protein productive value was significantly affected by water exchange rate after 2 months, while no differences in end weight were observed and no mortalities occurred during the experiment. A segmented linear regression analysis was used to identify the AFB induced effect on the fish approximated by the use of the specific growth rate (SGR). Pikeperch exhibited positive growth up to AFB values of 4000 mg L−1 but the threshold value for an AFB induced effect on SGR was identified at 1953 ± 613 mg L−1. As expected, the following water quality parameters showed a linear correlation with AFB: nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), total ammonia-nitrogen (TAN), total organic carbon (TOC), total carbon (TC) and total suspended solids (TSS) over the course of the experiment. Analysis of heavy metals and trace elements showed a linear correlation between AFB and phosphorus, arsenic, copper and potassium at the end of the experiment. The study quantified the functional relationship between AFB and water quality, as well as SGR. Additionally the present study was able to calculate the concentration of individual water quality parameters concomitant to the identified optimal AFB in order to provide reference points for future experiments as well as an approximation for commercial RAS for NO3-N, NO2-N, TAN, TOC, TC and TSS.

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