Fingerlings and marketable size rainbow trout (Oncorhynchus mykiss): Proximate composition, cholesterol content and fatty acid profile in fillets

Abstract

Rainbow trout (Onchorhynchys mykiss) is well known fish species in the nature. Changes in proximate composition of fish meat are associated with age and size of fish. Cholesterol content in animal tissues is associated with feeding method and quality of food, in spite of regulatory mechanism of cholesterol synthesis and absorption. Objective of this study was determination and comparison of proximate composition, cholesterol content and fatty acid profile of fingerlings and marketable size rainbow trout from aquaculture. Samples of fingerlings (average mass of 99 g and length of 18.6 cm) and marketable size rainbow trout (average mass of 229 g and length of 23.3 cm) were collected in August 2010, in the fishpond 'Ribnik', Mrkonjic city, Republic Srpska - Bosnia and Herzegovina. Fingerlings and marketable size rainbow trout were fed complete mixture of similar composition for both fish categories (fish products, oils and fats, cereal products and oil seeds). Obtained results showed that there was no statistically significant difference (p> 0.05) in the content of total lipids (3.81%, fingerlings and 4.17%, marketable size trout) and ash (1.27%, fingerlings and 1.29%, marketable size trout). Higher protein content was determined in marketable size trout fillets (18.69%), as well as lower water content (75.40%) compared to their content in fingerlings (17.72% proteins and 77.11% water). Cholesterol content was 82.59 mg/100g (fingerlings) and 70.12 mg/100g (marketable size trout). Statistically significant differences (p 0.05) in content of total n-6 fatty acids in fingerlings (16.76%) and marketable size fish (17.58%). Higher quantities of n-3 PUFA in fingerlings (17.17%) and commercial trout (19.20%) and lower quantities of n-6 PUFA (16.76% in fingerlings and 17.58% in marketable size trout) resulted in favourable n-3/n-6 ratio (1.02 in fingerlings and 1.09 in commercial trout). Content of eicosapentaenoic acid (EPA, C20:5 n-3) and docosahexaenoic acid (DHA, C22:6 n-3) was 2.78% and 8.21% in fingerlings and 3.36% and 9.29% in marketable size fish, respectively. Content of EPA+DHA in total fatty acids was 10.99% in fingerlings and 12.65% in marketable size rainbow trout. By consumption 200 g of this fish intake of desirable fatty acids, EPA and DHA, is 0.84 g in fingerlings, and 1.06 g in marketable size rainbow trout, which is in accordance with recommendation of the American Heart Association for persons with cardiovascular disease (daily intake: in total 1g EPA and DHA). Trout growth was accompanied by increase of the protein content, decrease of the water content and increase in content of PUFA especially n-3 essential fatty acids. Due to significant content of proteins and unsaturated fatty acids and lower amounts of fat, rainbow trout can be considered as one of the most valuable food stuffs in human nutrition.