Nannochloropsis gaditana and Crypthecodinium cohnii, two microalgae as alternative sources of essential fatty acids in early weaning for gilthead seabream

In this study, the feasibility of the use of heterotrophic dinoflagellate Crypthecodinium cohnii and phototrophic eustigmataceae Nannochloropsis gaditana as a partial or total substitute for fish oil in weaning diets of gilthead sea bream is evaluated. 20 day old larvae were fed with the following microdiets: a control diet based on fish oil, two diets with 11% dry weight of N. gaditana or with 8% of C. cohnii as substitutes for fish oil (diets N and C, respectively), and one last diet that combined N. gaditana (5.5%) and C. cohnii (5.5%) with fish oil (5.5%, diet N+C). At the end of the experiment (after 17 days of treatment), the survival did not differ among the groups, but the total length growth and dry weight of the larvae fed with fish oil and C. cohnii were superior to that of those fed with N. gaditana (p < 0.05). The analysis of fatty acids confirmed that C. cohnii and N. gaditana were used as a source of fatty acids essential in the microdiets of the larvae of gilthead sea bream. The results of this study revealed that the eicosapentaenoic acid (EPA; 20:5n-3) provided by N. gaditana allows the survival of the larvae, and that the docosahexaenoic acid (DHA; 22:6n-3) provided by C. cohnii is necessary in weaning diets in the gilthead sea bream in order to maintain the optimal growth of the larvae

Selenium inclusion decreases oxidative stress indicators and muscle injuries in sea bass larvae fed high-DHA microdiets

The objective of the present study was to determine the effect of Se inclusion in high-DHA and vitamin E microdiets (5 g DHA/100 g dry weight and 300 mg vitamin E/100 g dry weight; 5 g DHA/100 g dry weight and 300 mg vitamin E/100 g dry weight supplemented with Se) in comparison with a control diet (1 g DHA/100 g dry weight and 150 mg vitamin E/100 g dry weight) on sea bass larval growth, survival, biochemical composition, malonaldehyde (MDA) content, muscle morphology and antioxidant enzymes (AOE), insulin-like growth factors (IGF) and myosin expression. For a given DHA and vitamin E dietary content, Se inclusion favoured larval total length and specific growth rate, and reduced the incidence of muscular lesions, MDA contents and AOE gene expression. In contrast, IGF gene expression was elevated in the 5/300 larvae, suggesting an increased muscle mitogenesis that was corroborated by the increase in mRNA copies of myosin heavy chain. The results of the present study denoted the beneficial effect of Se not only in preventing oxidative stress, as a glutathione peroxidase cofactor, but probably due to other as yet unknown physiological functions

Modulation of the expression of components of the stress response by dietary arachidonic acid in European sea bass (Dicentrarchus labrax) larvae

This study reports for the first time in European sea bass, Dicentrarchus labrax (L.), larvae, the effect of different levels of dietary arachidonic acid (ARA; 20:4n-6) on the expression of genes related to the fish stress response. Copies of mRNA from genes related to steroidogenesis (StAR (steroidogenic acute regulatory protein), c-Fos, and CYP11β (11β- hydroxylase gene)), glucocorticoid receptor complex (GR (glucorticoid receptor) and HSP (heat shock proteins) 70 and 90) and antioxidative stress (catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX)) were quantified. Eighteen day-old larvae were fed for 14 days with three experimental diets with increasing levels of ARA (0.3, 0.6 and 1.2% d.w.) and similar levels of docosahexaenoic (DHA; 22:6n-3) and eicosapentaenoic (EPA; 20:5n-3) acids (5 and 3%, respectively). The quantification of stress-related genes transcripts was conducted by One-Step TaqMan real time RT-PCR with the standard curve method (absolute quantification). Increase dietary levels of ARA induced a significantly (p<0.05) down-regulation of genes related to cortisol synthesis, such as StAR and CYP11β and up-regulated genes related to glucocorticoid receptor complex, such as HSP70 and GR. No effects were observed on antioxidant enzymes gene expression. These results revealed the regulatory role of dietary ARA on the expression of stress-related genes in European sea bass larvae

Nannochloropsis gaditana and Crypthecodinium cohnii, two microalgae as alternative sources of essential fatty acids in early weaning for gilthead seabream

In this study, the feasibility of the use of heterotrophic dinoflagellate Crypthecodinium cohnii and phototrophic eustigmataceae Nannochloropsis gaditana as a partial or total substitute for fish oil in weaning diets of gilthead sea bream is evaluated. 20 day old larvae were fed with the following microdiets: a control diet based on fish oil, two diets with 11% dry weight of N. gaditana or with 8% of C. cohnii as substitutes for fish oil (diets N and C, respectively), and one last diet that combined N. gaditana (5.5%) and C. cohnii (5.5%) with fish oil (5.5%, diet N+C). At the end of the experiment (after 17 days of treatment), the survival did not differ among the groups, but the total length growth and dry weight of the larvae fed with fish oil and C. cohnii were superior to that of those fed with N. gaditana (p < 0.05). The analysis of fatty acids confirmed that C. cohnii and N. gaditana were used as a source of fatty acids essential in the microdiets of the larvae of gilthead sea bream. The results of this study revealed that the eicosapentaenoic acid (EPA; 20:5n-3) provided by N. gaditana allows the survival of the larvae, and that the docosahexaenoic acid (DHA; 22:6n-3) provided by C. cohnii is necessary in weaning diets in the gilthead sea bream in order to maintain the optimal growth of the larvae

Oxidative status and histological changes in sea bass larvae muscle in response to high dietary content of docosahexaenoic acid DHA

In previous studies, we observed dystrophic alterations in muscle of 48-day-old sea bass fed imbalanced docosahexaenoic acid (DHA) and vitamin E diets. To understand the whole pathological process associated with oxidative stress, a histological study was performed by feeding 14-day-old sea bass larvae with microdiets containing different ratios of DHA/vitamin E (1/150, 5/150 and 5/300) for a period of 21 days. Larvae fed diet 1/150 showed no lesions in contrast to larvae fed diets 5/150 and 5/300 where the highest incidence of muscle lesions and thiobarbituric acid reactive substances (TBARS) content was observed. Semithin sections revealed focal lesions consisting of degenerated fibres with hypercontracted myofilaments and extensive sarcoplasm vacuolization affecting both red and white muscle. Ultrathin sections of degenerating muscle fibres showed diffuse dilatation of sarcoplasmic reticulum, disorganized myofilaments and autophagic vacuoles containing myelin figures and dense bodies. Additionally, some macrophages were observed among injured fibres as numerous satellite cells. Results from the study agree with those obtained from previous work, proving the pathological potential of free radicals in sea bass larvae musculature. Moreover, high vitamin E inclusion could not completely protect cell membranes from free radicals action

Fish oil replacement by different microalgal products in microdiets for early weaning of gilthead sea bream (Sparus aurata, L.)

The aim of this study was to determine if algal products rich in DHA or ARA are able to completely replace fish oil in microdiets for marine fish larvae, gilthead seabream and if extra supplementation with EPA may further enhance larval performance. For that purpose, 20day-old gilthead seabream larvae of 5.97 +/- 0.4mm mean total length and 0.12 +/- 0.001mg mean dry body weight were fed with five microdiets tested by triplicate: a control diet based on sardine oil; a diet containing AquaGrow (R) DHA (diet DHA) to completely substitute the sardine oil; a diet containing AquaGrow (R) ARA (diet ARA); a diet containing both products, AquaGrow (R) DHA and AquaGrow (R) ARA to completely substitute the fish oil; and, a diet containing both products, AquaGrow (R) DHA and AquaGrow (R) ARA, together with an EPA source. Temperature, air and salinity activity tests were also performed to detect larval resistance to stress. At the end of the experiment, final survivals did not differ among groups. The microorganism produced DHA was able to completely replace fish oil in weaning diets for gilthead seabream without affecting survival, growth or stress resistance, whereas the inclusion of microorganism produced ARA did not improve larval performance. Moreover, addition of EPA to diets with total replacement of fish oil by microorganism produced DHA and ARA, significantly improved growth in terms of body weight and total length. The results of this study denoted the good nutritional value of microorganisms produced DHA as a replacement of fish oil in weaning diets for gilthead seabream, without a complementary addition of ARA. However, dietary supplementation of EPA seems to be necessary to further promote larval performance

Stress response in sea bream (Sparus aurata) held under crowded conditions and fed diets containing linseed and/or soybean oil

The physiological response to stressors in fish, including hormonal profiles and associated tissue responsiveness, is less documented. The aim of this study was to evaluate feeding gilthead sea bream (Sparus aurata) with diets containing linseed oil (LO) and soybean oil (SO) as substitutes to fish oil (FO) and their effect on fatty acid profile of head kidney and the consequent effect on stress response to a crowding challenge. Fish were fed 8 experimental diets with different levels of substitution 0% (FO), 70% (70LO, 70SO, 20LO50SO and 50LO20SO) and 100% (100LO, 100SO and 50LO50SO) over a period of 8 months. At the end of the feeding trial, samples of head kidney were collected for biochemical analysis and the fish were challenged by a crowding test. During the challenge, samples of plasma for cortisol analysis were collected at 0 h, 2 h, 5 h, 24 h, 48 h and 1 week in order to study acute and chronic stress responses. Results showed that fish fed vegetable oils (VO) had significantly decreased ARA, EPA, DHA and n-3 HUFA, while LA, LNA and total C18 PUFAs were significantly increased. The basal cortisol levels were significantly increased in fish fed 70LO, 100LO, 50LO20SO and 50LO50SO. The physiological response to crowding was significantly affected by the diet. After 2 h of crowding, all the treatments showed higher cortisol, with fish fed 100LO had significantly the highest response registering 131.38 pg/ml. After 5 h and 24 h, plasma cortisol was reduced in all treatments except in 50LO20SO. After 48 h of crowding, the plasma cortisol was increased in all treatments with the maximum value seen in fish fed 100LO (72.12 pg/ml). These levels were decreased in fish fed FO, 70LO, 100LO and 50L050SO after 1 week of crowding, but remained higher in fish fed 70SO, 100SO, 20LO50SO and 50LO20SO. In conclusion, fish fed LO diets showed the same response pattern as the control but with higher intensity regaining the basal levels after 1 week as the control, while fish fed SO had a slow response but changed the pattern characterized by a lower response at the beginning and longer recuperation without regaining the control value even after 1 week