64 MARCH 2013 • WORLD AQUACULTURE • WWW.WAS.ORG ˘ Cultured fish may have different chemical and sensory qualities compared to their wild counterparts. Chemical properties of cultured fish are related to feed composition and the culture system, whereas wild species are under the influence of environmental conditions and the availability of a range of natural food sources. Many studies show that the chemical properties of cultured fish are similar to wild fish and cultured fish are accepted and even preferred by many consumers. Fish that have polyunsaturated fatty acids in abundance are very susceptible to oxidation during processing and storage, resulting in loss of quality. Rosemary (Rosmarinus officinalis) is a natural herb with antioxidant activity. Rosemary can be incorporated into feed to increase resistance to product oxidation. Although including rosemary in fish diets has positive results, the effects on chemical composition have not been well studied. The effects on the chemical composition of rainbow trout fed with rosemary incorporated with the feed were investigated. Study Methods A commercially available feed with 45 percent protein, 18 percent fat, and 3 percent fiber was used in this study. Feed was pulverized to a powder and divided into three groups with powdered rosemary added at 3, 5, or 7 percent. After the addition of rosemary, the powdered feed was re-pelleted for use. Rosemary was purchased from a vendor in Mısır Bazaar. Rainbow trout (60 g; n = 210) were obtained from a fish farm at the Istanbul University, Faculty of Fisheries, Sapanca Inland Fisheries Research Center, Sapanca/Sakarya, Turkey. Fish were reared (30 per tank) at 12 ºC in 2.5-m3 fiberglass tanks that were supplied with continuous water flow (20 L/min) that maintained the oxygen saturation of outflow water greater than 70 percent. Each experimental group had 2 replications. Seven tanks were used (1 control, 6 experimental). Fish were fed 1.5 percent of the total tank biomass twice daily for 45 days. Every 15 days, fish were weighed to calculate the necessary feed amount. Twenty fish from each tank were weighed after 45 days and transferred to a laboratory for analyses. Moisture content was determined by drying minced samples in an oven at 105 ± 2 ºC for 3 h (Mattissek et al. 1992). Ash content was obtained by heating the residue for 3 h at 550º C (AOAC 1998a). Fat was extracted according to an acid hydrolysis method (Weilmeier and Regenstein 2004). Total nitrogen content was determined by the Kjeldahl method and was converted to crude protein content by multiplying by 6.25 (AOAC 1998b). Amino acid analysis was determined using high performance liquid chromatography5 (HPLC) (Erkan et al. 2010). Fatty acid composition was determined by Thermo Trace gas chromatography (GC) with an auto sampler6 equipped with a flame ionization detector (Ichihara et al. 1996). Results Feed intake reduced with increased concentration of dietary rosemary. There were no obvious effects of dietary rosemary on proximate composition of rainbow trout (Table 1). There was a modest increase in protein content as dietary rosemary concentration increased. Total amino acid concentration decreased as dietary rosemary increased. This effect was consistent for essential and non-essential amino acids. Non-essential amino acids, especially aspartic acid and glutamic acid, are responsible for the taste and flavors of fish. These non-essential amino acids decreased in rainbow trout as dietary rosemary increased (Table 2). The trend was consistent across all amino acids. Fatty acid composition of fish fed diets with added rosemary is given in Table 3. There are no clear trends in fatty acid composition of fish fed diets with graded levels of rosemary, although there was a modest increase in total mono-unsaturated fatty acid (MUFA) as dietary rosemary increased. Based on the results of this study, we recommend that dietary rosemary should not exceed 3 percent to avoid changes to proximate and fatty acid composition that would affect lipid oxidation (rancidity) and flavor. The Effects of Dietary Rosemary on the Chemical Composition of Rainbow Trout Ferhat Çagiltay*1, Nuray Erkan2, Arif Selçuk3, Özkan Özden2 TABLE 1. Proximate composition (%) of rainbow trout cultured with various concentrations of dietary rosemary. PROXIMATE COMPOSITION CONTROL 3% 5% 7% Moisture 78.6±1.7 78.2±0.1 78.3±1.4 79.8±1.8 Ash 1.16±0.09 1.85±0.21 1.84±0.15 1.70±0.09 Protein 16.5±0.5 18.0±1.0 18.7±0.4 18.7±0.4 Fat 5.03±0.08 5.15±0.68 5.40±0.08 3.20±0.15
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