Reda Saleh

ABSTRACT 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, 20 day‐old gilthead seabream larvae of 5.97 ± 0.4 mm mean total length and 0.12 ± 0.001 mg mean dry body weight were fed with five microdiets tested by triplicate: a control diet based on sardine oil; a diet containing AquaGrow® DHA (diet DHA) to completely substitute the sardine oil; a diet containing AquaGrow® ARA (diet ARA); a diet containing both products, AquaGrow® DHA and AquaGrow® ARA to completely substitute the fish oil; and, a diet containing both products, AquaGrow® DHA and AquaGrow® 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.

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.

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.

ABSTRACT The inclusion of complementary antioxidative factors, such as selenium (Se), could counteract the high oxidation risk in early weaning diets high in polyunsaturated fatty acids (PUFA). The present study investigated the effects of graded levels of Se derived yeast with krill phospholipids (KPL) on skeletal development, survival, stress resistance, oxidative status and biochemical composition of seabream larvae. Seabream larvae were completely weaned at 16 dph and fed five microdiets for 30 days with different levels of Se: 2SE, 4SE, 6SE, 8SE and 12SE (1.73, 3.91, 6.41, 8.47, 11.65 mg kg− 1 dietary dry weight, respectively). Increases in Se up to 11.65 mg kg− 1 dietary dry weight significantly improved survival rate (54%) and stress resistance, but did not affect larval growth. Seabream larvae fed diets supplemented with 12SE (11.65 mg kg− 1) showed a gradual increase in this mineral according to dietary Se levels, denoting the progressive absorption of this nutrient. The degree of larval lipid oxidation, as indicated by malondialdehyde (MDA) content and antioxidant enzyme (AOE) gene expression, was significantly lower in larvae fed 8SE and 12SE diets compared to those fed 2SE and 4SE diets. Furthermore, a reactive response as a result of Se inclusion was observed by the increase in osteocalcin, osteonectin, osteopontin, alkaline phosphatase and matrix gla protein gene expression in larval tissues, suggesting a well skeletal development. These results denoted the high efficiency of Se as an antioxidant factor and the importance of the inclusion of adequate levels (11.65 mg Se kg− 1 diet) in early weaning diets.

The aim of the present study was to determine the influence of different levels of dietary phospholipids (PL) on the development of gilthead sea bream (Sparus aurata) larvae. Larvae were fed from 17 to 31 day post hatching (dph) five formulated microdiets with different levels of krill phospholipids (PL) (0, 1, 2, 4 and 6 PL %). Highest growth, survival and resistance to stress was found in larvae fed 6% dietary PL although without significant difference with larvae fed 4 % PL, (8.68±0,24 & 8.43±0.34 mm in TL and 47.92±1.54 & 47.71±4.34 % survival rate, for 6 and 4 % PL respectively). Biochemical composition of larvae (31 dph) fed 4 and 6 % dietary PL showed significantly higher total lipid content, and total n-3HUFA,