Total replacement of fish oil by soybean or linseed oil with a return to fish oil in turbot (Psetta maxima)

Abstract

The aim of the study was to investigate the replacement of fish oil by vegetable oils and the effects of a washout with a return to fish oil on growth performances and lipid metabolism. Three experimental fish meal based, isonitrogenous (crude protein content: 57.5%) and isolipidic (crude lipid content: 16.5%) diets, were formulated containing either 9% of added fish oil (FO), soybean oil (SO) or linseed oil (LO). Each diet was distributed to triplicate groups of 25 marketable size turbot (initial body weight of 579 g) grown in seawater at a water temperature of 17°C. Fish were fed once a day to visual satiety. At the end of the growth trial which lasted 13 weeks, all groups of turbot were fed FO diet for 8 weeks. The growth of turbot was high, but the incorporation of vegetable oils in the diets resulted in a slight decrease in growth as compared to those fed the fish oil based diet. Feed and protein efficiency and whole body composition were not affected by dietary lipid sources. Total lipid content was low in the muscle of turbot (below 2%), ventral muscle being fatter than dorsal muscle. Liver and muscle fatty acid (FA) composition reflected dietary FA composition. Liver and muscle of fish fed SO diet were rich in 18:2n-6 whereas those of fish fed LO diet were rich in 18:3n-3. Liver and muscle of fish fed SO and LO diets had lower levels of 20:5n-3 and 22:6n-3 in comparison to those of fish fed FO diet. In turbot, hepatic lipogenic enzyme activities were low and not influenced by dietary lipid source. At the end of the second period, after transfer to FO based diets, muscle FA composition of fish fed previously SO and LO diets was still different to those of fish fed the FO diet. The values of 18:2n-6 and 18:3n-3 respectively were lower than the values found at the end of the growth period but higher than those of fish fed the FO diet. An increase of FA levels, characteristic of fish oil, was observed in the liver and muscle of fish previously fed vegetable oils. Data obtained show that replacement of fish oil by vegetable oils is possible without any significant impact on growth performance of turbot, that dietary lipids are an effective vector to influence the nutritional quality of finished product and that a duration of 8 weeks is not sufficient to bring the FA profile of turbot of this size back to that of fish fed fish oil over the whole period.

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“…This result is consistent with a previous study on European sea bass in which it was suggested that LA was quickly deposited into fish tissues, but when supplied in surplus, it was also readily utilized for β-oxidation for energy production. Similar observations were also made for different species (Bell et al, 2001;Regost et al, 2003;Caballero et al, 2004).…”

“…This has also been observed in marine carnivorous species such as red sea bream, Pagrus major (Huang et al, 2007); turbot, Psetta maxima (Bell et al, 1994;Regost et al, 2003) and European sea bass (Mourente et al, 2005a). Accordingly, in the present study some fillet fatty acid concentrations were very closely correlated with dietary fatty acid concentrations, recording R 2 values higher than 0.8 (such as 14:0, 18:2n-6, 20:5n-3 and 22:6n-3), as previously reported (Bell et al, 1998;Bell et al, 2001;Bell et al, 2002).…”

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“…It appeared that while dietary fatty acids influence fillet fatty acids, DHA was selectively retained in the muscle compared to other fatty acids. Higher levels of DHA in fish fillets in comparison to the concentration present in the diet was also observed in Atlantic salmon (Bell et al, 2001, rainbow trout, Oncorhynchus mykiss (Caballero et al, 2002) and turbot, Psetta maxima (Bell et al, 1994;Regost et al, 2003). The possible mechanisms underlying this selective deposition include the high specificity of fatty acyl transferase for DHA.…”

Nutritional and Fatty Acids Profile Analyses of Commonly Consumed Fresh Water Fish Species in Pakistan

“…These findings are in accord with the findings of Guil-Guerrero et al (2011), High prevailing quantity of SFAs may be due to less efficiency of fish species in utilizing the SFAs as core energy source which resulted in the rise of SFAs (Nath and Banerjee, 2012). Regost et al (2003) stated that De novo synthesis and diets are the two sources of fatty acids in muscles. If the fish feed mostly on the diet mainly insects and other aquatic then the saturated fatty acids contents rises and if they feed on the plant and algae sources then it contain mostly unsaturated fatty acids.…”

“…Total PUFAs varied from 7.8% (W. atto) to 22.61% (L. rohita) with γ-linolenic acid (GLA, C18:3ώ6), α-linolenic acid (ALA, C18:3ώ3) and cis-8, 11, 14 Eicosatrienoic (hGLA, C20:3ώ6)as prevalent FAs in W. atto and C. marulius and Linoleic acid (LA, C18:2ώ6), γ-linolenic acid (GLA, C18:3ώ6), cis-8, 11, 14 Eicosatrienoic (hGLA, C20:3ώ6), Docosahexaenoic acid (DHA, C22:6ώ3) in L. rohita and A. anguilla respectively. This divergence arose among these species due to various factors such as state of their reproductive cycle, organ source, habitat, size, season and sex (Regost et al, 2003). Table 2, showed the amount of PUFAs present in the oil of four species.…”