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FEATURE

ENHANCING PERFORMANCE Phosphorus digestibility and retention in gilthead seabream

I

by S. Zwart1, M.E. Castellón2 and S. Deguara2 Aliphos Rotterdam B.V., Zevenmanshaven Oost 139, 3133 CA Vlaardingen (The Netherlands) 2 AquaBioTech Group, ‘Central Complex’, Naggar Str., Targa Gap, Mosta MST 1761 (Malta).

1

ntensive fish farming is a source of organic and inorganic nutrients such as nitrogen and phosphorus, which can cause eutrophication in natural aquatic ecosystems (Porrello et al., 2003). Phosphorus is an essential nutrient in feeds for the proper growth and feed performance in fish (Pimentel Rodrigues and Oliva-Teles, 2001). Generally, fish feeds that are based on fishmeal as the main ingredient provide a total Phosphorus content that surpasses the minimal requirements needed to obtain optimal growth (Pimentel Rodrigues and Oliva-Teles, 2001). New feeding and formulation strategies aim to reduce the environmental impacts of aquaculture activities by minimizing the nutrient loading entering the natural waters. One of these approaches consists in a full or partial substitution of fishmeal with other ingredients with the addition of inorganic Phosphorus salts, as necessary, an approach which has led to a reduction in the excretion of Phosphorus with no negative effect on growth (Hernández et al., 2005). The present study was undertaken to analyse the effect of two different commercially available inorganic Phosphorus sources, Aliphos® Monocal (monocalcium phosphate, MCP) and Windmill® Aquaphos (monoammonium phosphate, MAP), on the performance and phosphorus digestibility and retention in gilthead sea bream, Sparus aurata.

Materials and methods

To compare the effect of the two commercial phosphate sources

Figure 1a

Figure 1b

on the feed utilization and growth of gilthead sea bream, 3 fishmeal-free diets were studied in a recirculation aquaculture system (RAS) available at the AquaBioTech Innovia facilities (Malta). The control diet (diet CD) was not supplemented with any additional phosphorus source while the other diets were supplemented with either of the two commercially available products, MCP (diet MCPD) and MAP (diet MAPD) to achieve an estimated digestible phosphorus content of 0.45% and Ca to digestible P ratio of 1.40. Yttrium oxide was added to the diets as an inert marker to enable the determination of the apparent digestibility coefficient (ADC) of Phosphorus. During the growth trial, 85 2.8g (initial weight) gilthead sea bream were fed at a fixed regime four times a day; each one of the three treatments was administered in triplicate. All fish were weighed in bulk at the beginning and end of the trial whilst 50 fish were weighed every 2 weeks until the end of the trial. For the determination of the apparent Phosphorus digestibility coefficient (ADC) of the diets, 40 fish, of 17g average weight, were placed into the tanks in triplicate and the collection of faeces was carried out by stripping.

The Results

By the end of the experiment, gilthead sea bream fed the diet MAPD showed a significantly better specific growth rate and lower feed conversion rate than fish fed with MCPD or CD (Figure 1a). Phosphorus retention by fish fed MAPD was significantly higher in comparison with the other two diets (Figure 1b); the Phosphorus available in MAP was found Figure 1a: Results to be much better retained than of specific growth rate (SGR) and the Phosphorus in MCP (58% feed conversion vs. 31%). ratio (FCR) (a) and Phosphorus retention Dietary Phosphorus ADC was and Phosphorus ADC significantly different between (b) of fish fed with the treatments; fish fed MAPD experimental diets. Figure 1b: Phosphorus showed a significantly higher retention and Phosphorus ADC, followed by Phosphorus ADC values obtained for each one that of fish fed MCPD (Figure of the diets 1b); the Phosphorus available in

16 | January 2017 - International Aquafeed

JAN 2017 - International Aquafeed magazine