Lipid digestion capacity in gilthead seabream (Sparus aurata) from first feeding to commercial size.

To characterise the progression of lipid digestion capacity in gilthead seabream across life cycle, the activities of bile salt-activated lipase (BAL) and phospholipase A2 (PLA2) were determined in the digestive tracts of cultured gilthead seabream from first feeding to marketable size (49 µg to 300 g). Four trials were undertaken with gilthead seabream of different ages, fed on diets with fishmeal and fish oil as the main dietary protein and lipid sources and 21-25% lipid contents. Larvae of 4 days after hatching (dah) to 9 dah were fed rotifers with different fatty acid profiles: control (2.8% eicosapentaenoic acid, EPA; 1.6% docosahexaenoic acid, DHA; 5.4% n-3 long-chain polyunsaturated fatty acids, n-3 LC-PUFAs; and 0.2% arachidonic acid, ARA), low EPA (1.38% EPA, 1.6% DHA, 3.9% n-3 LC-PUFA and 0.4% ARA) or low LC-PUFA (0.7% EPA, 1.0% DHA, 1.8% n-3 LC-PUFA and 0.0% ARA) (% dry weight). Larvae fed the low-LC-PUFA diet showed a significantly lower growth at 10 dah. BAL activities were significantly higher in larvae fed the control diet than in those fed low-EPA and low-LC-PUFA diets at 9 dah. BAL activity increased with age across life cycle (49 µg to 300 g). PLA2 activity could not be detected in larvae but increased with age in juvenile and adult gilthead seabream (86 g to 295 g), similar to BAL. Results suggested a correspondence between the stimulation of lipid digestion capacity and growth performance in gilthead seabream by dietary essential fatty acids, particularly by EPA when DHA requirements are met in the diet especially in the very early stages of life cycle, when the progression of BAL and PLA2 activities could be used as indicators of the nutritional status of cultured gilthead seabream larvae. Finally, regarded that PLA2 activity was not detected in 4-dah to 44-dah gilthead seabream larvae, future works are suggested to assess the dietary effect on PLA2 activity and the PLA2 activity pattern along the larval stage of this species using a more sensitive detection method.

Fatty Acid Profile of Neutral and Polar Lipid Fraction of Wild Eggs and Hatchlings from Wild and Captive Reared Broodstock of Octopus vulgaris.

The culture of Octopus vulgaris is constrained by unsolved problems in paralarvae rearing, mainly associated to the unknown nutritional requirements of this species in early stages. In this article we studied the fatty acid profile (total, neutral, and polar lipid fractions) in wild eggs and wild hatchlings, collected in Gran Canaria (SW) (Spain) with artificial dens, in comparison to hatchlings obtained in captivity from broodstock fed on trash fish species. Total lipids were 11.5-13.5% dw, with the polar fraction representing a 70.6-75.5% of total lipid, with lower values in wild hatchling in comparison with captive ones. Docosahexaenoic acid (DHA) was the main component in neutral and polar fatty acid profile in all samples, underlying its importance in this species. Decreasing levels of saturates and arachidonic acid (ARA) from wild eggs to hatchlings, mainly associated to the polar fraction, suggest their use during embryonic development. In hatchlings, increasing levels of oleic acid in the neutral fraction and eicosapentaenoic acid (EPA) in the polar fraction, suggests their importance in hatchlings quality. Wild hatchlings showed in the polar fraction higher oleic acid and ARA, and lower DHA/ARA and EPA/ARA ratios in comparison with captive hatchlings, suggesting a difference in paralarvae nutritional status. These results suggest the importance of n-3 highly unsaturated fatty acids (HUFA), oleic acid, and ARA, presented in the adequate lipid fraction, in the diet of broodstock and paralarvae of O. vulgaris.

Physiological pathways involved in nutritional muscle dystrophy and healing in European sea bass (Dicentrarchus labrax) larvae.

The potential muscle regeneration after nutritional dystrophy caused by high dietary DHA contents in fish and the physiological pathways involved are still unknown. To better understand this process, an experiment was conducted for 3 weeks in 14 day-old European sea bass larvae using different DHA ratios (1 or 5%). After this period, part of the larvae fed 5% DHA diet was switched to 1% DHA diet ("wash-out") for another 2 weeks. Larvae fed 5% DHA diet showed altered oxidative status as indicated by the highest TBARS values, antioxidant enzymes (AOE) expression and incidence of muscular lesions. Accordingly, "washed-out" larvae showed lower dry weight and α-TOH content. IGF-I gene expression was elevated in 5% DHA larvae at 35 dph, suggesting increased muscle mitogenesis that was corroborated by the increase in myosin heavy chain expression. It can be concluded that high dietary DHA contents alter the oxidative status and cause muscular lesions in European sea bass larvae, with morphological and molecular aspects of mammalians muscular degenerative disease.

Vitamin C enhances vitamin E status and reduces oxidative stress indicators in sea bass larvae fed high DHA microdiets.

Docosahexaenoic acid (DHA) is an essential fatty acid necessary for many biochemical, cellular and physiological functions in fish. However, high dietary levels of DHA increase free radical injury in sea bass (Dicentrarchus labrax) larvae muscle, even when vitamin E (α-tocopherol, α-TOH) is increased. Therefore, the inclusion of other nutrients with complementary antioxidant functions, such as vitamin C (ascorbic acid, vitC), could further contribute to prevent these lesions. The objective of the present study was to determine the effect of vitC inclusion (3,600 mg/kg) in high DHA (5% DW) and α-TOH (3,000 mg/kg) microdiets (diets 5/3,000 and 5/3,000 + vitC) in comparison to a control diet (1% DHA DW and 1,500 mg/kg of α-TOH; diet 1/1,500) on sea bass larvae growth, survival, whole body biochemical composition and thiobarbituric acid reactive substances (TBARS) content, muscle morphology, skeletal deformities and antioxidant enzymes, insulin-like growth factors (IGFs) and myosin expression (MyHC). Larvae fed diet 1/1,500 showed the best performance in terms of total length, incidence of muscular lesions and ossification degree. IGFs gene expression was elevated in 5/3,000 diet larvae, suggesting an increased muscle mitogenesis that was confirmed by the increase in the mRNA copies of MyHC. vitC effectively controlled oxidative damages in muscle, increased α-TOH larval contents and reduced TBARS content and the occurrence of skull deformities. The results of the present study showed the antioxidant synergism between vitamins E and C when high contents of DHA are included in sea bass larvae diets.

Regulation of growth, fatty acid composition and delta 6 desaturase expression by dietary lipids in gilthead seabream larvae (Sparus aurata).

The Delta6 and Delta5 desaturases and elongases show only very limited activity in marine fish, and little is known of the possibility of enhancing Delta6 desaturase gene expression in these fish. The use of plant oils in marine fish diets is limited by their lack of n-3 highly unsaturated fatty acids (HUFA) despite an abundant content of the 18C fatty acid precursor linoleic and alpha-linolenic acids. The objective of the present study was to determine the ability of larval gilthead seabream to utilize vegetable oils and assess the nutritional regulation of Delta6 desaturase gene expression. Seventeen-day-old gilthead seabream larvae were fed during a 17-day period with one of four different microdiets formulated with either sardine fish oil (FO), soybean, rapeseed or linseed oils, respectively, or a fifth diet containing defatted squid meal and linseed oil. Good larval survival and growth, both in terms of total length and body weight, were obtained by feeding the larvae either rapeseed, soybean or linseed oils. The presence of vegetable oils in the diet increased the levels of 20:2n-9 and 20:2n-6, 18:2n-9, 18:3n-6, 20:3n-6 and 20:4n-6, in larvae fed rapeseed and soybean oils in comparison to those fed FO. In addition, a sixfold increase in the relative expression of Delta6 desaturase-like gene was found in larvae fed rapeseed and soybean oils, denoting the nutritional regulation of desaturase activity through its gene expression in this fish species. However, feeding linseed oil did not increase the expression of the Delta6 desaturase gene to such a high extent.