World Aquaculture September 2018

64 SEP TEMBER 2018 • WORLD AQUACULTURE • WWW.WA S.ORG practical ingredients that fulfilled the nutritional requirements of seabream juveniles, low levels of marine-derived protein (19 percent), and high levels of plant-derived protein (pea protein concentrate, soybean meal, wheat gluten and corn gluten) (Table 2). The diet was supplemented with selected essential amino acids and inorganic phosphorus to avoid nutritional deficiencies. Two additional experimental diets were formulated based on the CTRL diet: a commercial blend of anise, citrus, and oregano essential oils 1 at 1.2 g/kg (diet Phyto C), and a similar blend in encapsulated form 2 at 0.2 g/kg (diet Phyto E). Triplicate groups of 20 seabream juveniles, with a mean initial body weight of 28 ± 2 g were fed one of the three experimental diets for 63 days. Fish were grown in 100- L circular plastic tanks supplied with flow-through seawater at 24 ± 2 C and dissolved oxygen levels above 7 mg/L, in a 12 h light - 12 h dark cycle. Maximization of Protein and Fat Retention and Reduction of Nitrogenous Losses Voluntary feed intake was not affected by the different dietary supplementations, suggesting that were no differences in feed palatability among diets due to the presence of the essential oils. The different dietary supplementations had similar effects on FBW, daily weight gain, SGR, VFI, FCR, and PER of seabream juveniles (Table 3). Moreover, the ADC of dry matter and protein was not affected by the different dietary supplementations. Protein and fat retention (Fig. 1) and N budget (Fig. 2) were calculated based on weight gain, feed intake, ADC, and whole- body composition. Both Phyto C and Phyto E diets significantly enhanced fat retention, whereas only Phyto E significantly enhanced protein retention. Daily nitrogen gain was similar among dietary treatments (0.37 to 0.38 g N/kg/day; P = 0.90), but metabolic and fecal nitrogenous losses were somewhat lower in fish fed Phyto E (metabolic loss: 0.81±0.01 g N/kg/day; fecal loss 0.09±0.01 g N/kg/day) than CTRL (metabolic loss: 1.00±0.09 g N/ kg/day; fecal loss 0.11±0.01 g N/kg/day) diet. Conclusion This research indicated that adding a commercially available blend of anise, citrus, and oregano essential oils to a low FM diet positively affected protein and fat retention, and reduced nitrogenous losses. No significant differences were observed on performance and digestive processes of juvenile seabream, regardless of whether the encapsulated formula was used or not, although the short experimental period may contribute to the lack of statistical differences. Dietary supplementation of a low FM diet with the phytogenic essential oils tested resulted in a non-significant but notable reduction of FCR values (Table 3). In absolute terms, the reduction ranged from 9 percent in the Phyto C diet to 12 percent in the Phyto E diet, bringing some economic advantages for farmers. The FCR observed in the present study, together with the similar feed intake among experimental treatments, significantly enhanced protein and fat retention in seabream fed the two supplemented diets (Fig. 1). Protein retention can be associated with increased growth and/or low FM diet, and fat retention can be associated with increased energy. The estimated parameters associated with dietary protein utilization suggest that protein retention in seabream fed Phyto C and Phyto E was driven by decreased nitrogenous metabolic and fecal losses (Fig. 2) rather than by improved protein deposition. Notes Rui Gonçalves, Scientist – Aquaculture at BIOMIN Rui.goncalves@biomin.net Vera Rodrigues, Rita Colen, Laura Ribeiro, Gonçalo Santos, Jorge Dias 1 Digestarom ® P.E.P. 1000 2 Digestarom ® P.E.P. MGE 150 FIGURE 1. Protein and fat retention in gilthead seabream fed the three experimental diets for 63 days. Bars are means ± s. d. (n = 3). Different letters above bars denote significant differences (Tukey’s HSD, P <0.05). CTRL – control diet (Rodrigues et al. 2018). FIGURE 2. Daily nitrogen (N) budget in gilthead seabream fed the three experimental diets for 63 days. Bars are means ± s. d. (n = 3). N gain = final carcass N content – initial carcass N content. Fecal N loss = crude N intake x (100 – ADC Nitrogen). Metabolic N losses = digestible N intake – N gain. Different letters within bars denote significant differences (Tukey’s HSD, P <0.05) among treatments for fecal N losses and metabolic losses. n.s. – non- significant (P >0.05) (Rodrigues et a l. 2018).