Dietary protein source affects lipid metabolism in the European seabass (Dicentrarchus labrax).

The study was undertaken to evaluate the effects of dietary protein sources on lipogenesis and fat deposition in a marine teleost, the European seabass (Dicentrarchus labrax). Four isonitrogenous (crude protein (CP, Nx6.25), 44% DM) and isoenergetic (22-23 kJ/g DM) diets were formulated to contain one of the following as the major protein source: fish meal (FM), one of two soy protein concentrates (SPC) and corn gluten meal (CGM). Apparent digestibility coefficients of the diets and raw ingredients, as well as soluble nitrogen (ammonia and urea) and phosphorus excretion were measured. Growth rates of seabass fed plant protein-based diets were significantly lower than those fed fish meal based diet. The protein utilisation was strongly correlated to the dietary essential amino acids index. Measurements of N excretion (ammonia and urea nitrogen) confirmed these data. Daily fat gain at the whole body level ranged between 1.1 to 1.7 g/kg BW, with the highest values being recorded in fish fed the fish meal based diet. Levels of plasma triglycerides and cholesterol were lower in fish fed soy protein diets than in those fed the diet solely based on fish meal. Soy protein rich diets decreased the activities of selected hepatic lipogenic enzymes (glucose 6-phosphate dehydrogenase, malic enzyme, ATP-citrate lysase, acetylcoenzyme A carboxylase and fatty acid synthetase). Highest lipogenic enzyme activities where found in fish fed the fish meal diet, except for fatty acid synthetase which was increased in seabass fed the corn-gluten meal based diets. Overall data suggest that dietary protein sources affects fat deposition and the lipogenic potential in European seabass.

The partial substitution of digestible protein with gelatinized starch as an energy source reduces susceptibility to lipid oxidation in rainbow trout (Oncorhynchus mykiss) and sea bass (Dicentrarchus labrax) muscle.

We evaluated the influence of dietary gelatinized starch and protein on the fatty acid composition of muscle in rainbow trout and European sea bass and on the susceptibility of flesh to lipid peroxidation. The possibility that flesh peroxidation could be accounted for by lipogenesis and the deposition of fat was also explored. The inclusion of gelatinized starch in the diet of rainbow trout improved growth with respect to that observed in fish fed crude starch (P<.001). This was especially noticeable at the lowest concentration of dietary protein tested (P = .037); suggesting that gelatinized starch may partially replace protein in the production of energy without inducing a negative effect on growth. However, in European sea bass, the gelatinization of starch and dietary protein concentration showed no significant effect on final body weight. The intramuscular neutral lipid concentration of the sea bass was reduced by the gelatinization of dietary starch (P = .034). The highest dietary protein concentration increased the proportion of saturated fatty acids in the neutral (P = .0742) and polar (P = .0033) lipid fractions. The dietary inclusion of high levels of protein in rainbow trout led to a lower concentration of total (n-3) (P = .0457) and (n-6) (P = .0522) fatty acids and a higher concentration of total monounsaturated fatty acids (P = .0006). The inclusion of gelatinized starch led to a lower concentration of (n-3) fatty acids (P = .0034) and a higher concentration of saturated fatty acids (P = .0007). The polar fraction was hardly affected by the same treatment. A significantly lower susceptibility of the dorsal muscle to oxidation was observed in groups of European sea bass fed gelatinized starch (P<.01). A similar trend was observed in rainbow trout, although differences were not significant. The findings suggest that the digestible protein concentration of nutrient-dense diets for rainbow trout and European sea bass can be reduced with a beneficial effect on tissue lipid oxidation and no negative effects on growth and muscle composition.

Dietary fish oil and digestible protein modify susceptibility to lipid peroxidation in the muscle of rainbow trout (Oncorhynchus mykiss) and sea bass (Dicentrarchus labrax).

The effects of dietary fish oil and digestible protein (DP) levels on muscle fatty acid composition and susceptibility to lipid peroxidation were studied in two representative fish species for human nutrition, from fresh and seawater, rainbow trout (Oncorhynchus mykiss) and European sea bass (Dicentrarchus labrax). In rainbow trout, higher concentrations of dietary fat and DP led to higher weight gain (g/d) (P = 0.001 and P = 0.043 respectively). Additionally, an interaction effect was observed in this species, since the effect of DP was only evident when the dietary fat concentration was low (P = 0.043). A similar tendency was also observed in European sea bass, although with less marked differences among nutritional treatments. Trout fed on diets with a higher concentration of dietary fat had higher concentrations of intramuscular total and neutral lipids in the dorsal muscle (P = 0.005). Increased levels of dietary DP led to significantly lower concentrations of polar lipids in the dorsal muscle of both rainbow trout (P = 0.005) and European sea bass (P = 0.006). In the neutral fraction of intramuscular lipids of dorsal muscle the concentration of n-3 fatty acids was positively affected by the dietary fat concentration in both rainbow trout (P = 0.04) and sea bass (P = 0.001). Muscle homogenates from trout and sea bass fed on diets rich in fish oil showed a significantly higher susceptibility to oxidation than muscle homogenates from fish fed on low-fat diets (P = 0.001). The higher DP concentration also increased susceptibility to oxidation. Moreover, in rainbow trout an interaction effect was observed where the pro-oxidant effect was of higher magnitude when the dietary concentration of both nutrients, fat and protein, was high (P = 0.004).