Abstract
Gilthead sea bream (Sparus aurata) was raised in six individual recirculating aquaculture systems (RAS) whose biofilters’ performance was analyzed. Fish were fed with three different diets (a control diet, a fishmeal-based diet (FM), and a plant meal-based diet (VM)) and with three different feeding strategies (manual feeding to apparent satiation, automatic feeding with restricted ration, and auto-demand feeding). For every combination of diet and feeding strategy, the mean oxygen consumption, ammonia excretion, and ammonia removal rate were determined. Fish fed with the VM diet consumed the most oxygen (20.06 ± 1.80 gO2 consumed kg−1 day−1). There were significant differences in ammonia excretion depending on the protein content and protein efficiency of the diet, as well as depending on feeding strategy, which in turn affected ammonia removal rates. Fish fed by auto-demand feeders led to the highest mean ammonia removal rate (0.10 gN-TAN removed m−2 biofiltration area day−1), while not leading to peaks of high ammonia concentration in water, which preserve fish welfare and growth.
Highlights
In recirculating aquaculture systems (RAS), in which the hydraulic residence time is as large as possible, ammonia is usually removed by nitrifying biofilters, adopted from wastewater treatment (Liao and Mayo 1972)
Since there is no general recommendation on fish feeding strategy and fish diet for maximizing biofilter performance, this paper aims to evaluate daily nitrogen variations based on the selection of three specific diets and three feeding strategies with the objective to determine differences on nitrification rates
This article reports an essay of marine water fish production (Sparus aurata in this case) in a pilot-scale RAS with appropriately sized biofilters fed with experimental diets compared to a control diet, with focus on biofilter efficiency
Summary
In recirculating aquaculture systems (RAS), in which the hydraulic residence time is as large as possible, ammonia is usually removed by nitrifying biofilters, adopted from wastewater treatment (Liao and Mayo 1972). Several factors that affect nitrification performance include reactor-specific parameters (filter media, hydraulic loading) as well as water quality parameters such as temperature, influent ammonia concentration, pH, or organic matter (Eding et al 2006). The effect of these factors on nitrification rate has been investigated by several authors, with or without including live fish on their experiments (Zhu and Chen 1999; Godoy-Olmos et al 2016, 2019). Several authors have stated 1⁄2-order substrate-dependent kinetics (Salvetti et al 2006; Díaz et al 2012; von Ahnen et al 2015), and whereas the quantification of the effects of other parameters has been reported as well, their effect is somewhat less influential (Lyssenko and Wheaton 2006)
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