Lutein enrichment of the rotifer Brachionus sp. using freeze‐dried Muriellopsis sp. cells

Rotifers, used in aquaculture as feed for early larval stages, are poor in carotenoids compared with copepods, the natural most common prey item of marine fish larvae. A minimal sufficient level of carotenoids in fish larvae may be essential for a correct development. The freshwater microalga Muriellopsis sp. has been identified as a potential source of the carotenoid lutein with possible application in aquaculture. Lutein is a potent antioxidant, with potentially beneficial effects as a carotenoid for fish larvae. This study describes the lutein enrichment of the rotifer Brachionus sp. when incubated with homogeneously dispersed suspensions of freeze‐dried, lutein‐rich Muriellopsis sp. in seawater. A short enrichment time (2 or 2.5 h) resulted in a higher lutein content of the rotifers than a long enrichment time (13.5 or 24 h). Although the concentration of lutein in enriched rotifers, 0.06–0.16 mg (g dry weight)^?1 was low compared with its content in Muriellopsis sp. [about 3 mg (g dry weight)^?1], it was in the range reported for natural copepod populations. Therefore, we conclude that freeze‐dried biomass of Muriellopsis sp. can be used to enrich rotifers with lutein, providing an adequate level of this carotenoid for marine fish larvae.     

Effects of inulin and fructooligosaccharides on growth performance,body chemical composition and intestinal microbiota of farmed rainbow trout (Oncorhynchus mykiss)

The objectives of the present study were to investigate the effects of inulin and fructooligosaccharides (FOS) on growth performance, whole body and fillet chemical composition and intestinal microbiota of rainbow trouts reared under fish farming conditions. Trouts fed inulin‐ or FOS‐containing diets (5 and 10 g kg^?1) exhibited significant (P = 0.030) body weight gain improvements compared with controls. An increase in gross energy (P = 0.044) and Ca content (P = 0.034) in the whole body of trouts was observed for prebiotic treatments. A decrease in crude protein content (P = 0.009) and a tendency to increase total lipid and gross energy contents (P = 0.090 and P = 0.069, respectively) were detected in the fillet tissue for prebiotic treatments. These results clearly indicate that inulin and FOS improved the intestinal absorption of Ca and that the increased amount was predominantly incorporated into bone tissue. Inulin reduced (P = 0.027) the intestinal population of Vibrio spp. in the distal region to such an extent that no viable counts were detected. The presence of Flavobacterium spp. was not detected in any group, and the numbers of Aeromonas spp., Pseudomonas spp. and Gram‐positive bacteria were not affected (P > 0.05).     

Maslinic acid,a natural triterpene,and ration size increased growth and protein turnover of white muscle in gilthead sea bream (Sparus aurata)

Maslinic acid (MA) is a pentacyclic triterpene used, at experimental level, as an additive to stimulate growth, protein‐turnover rates and hyperplasia in fish. In this experiment we have studied the effects of feeding with MA at daily fixed ration of 10 g kg^?1 of body mass, on growth, protein‐turnover rates and nucleic acid concentration in white muscle of gilthead sea bream grown in a local fish farm. The experimental groups contained 0 (control), 50 (MA₅₀) and 100 (MA₁₀₀) mg MA per kg of diet. Two groups were provided feed ad libitum (control AL and MA₁₀₀AL), while three were given a fixed ration (control R, MA₅₀R, and MA₁₀₀R). We have determined the following: growth rate; nucleic acid and protein levels; relative and absolute protein‐accumulation (K_G, A_G), synthesis (K_S, A_S) and degradation (K_D, A_D) rate, protein‐synthesis capacity (C_S), protein‐synthesis efficiency (K_RNA), protein‐synthesis rate per DNA (K_DNA) and protein‐retention efficiency. At the end of the experiment, higher body weights and muscle growth rates were found in both groups of fish fed with 100 mg MA per kg of diet. Feed‐efficiency rate, protein‐efficiency ratio and protein productive value, were higher in the MA₁₀₀AL group than in control AL. Fractional and absolute protein‐synthesis and degradation rates in white muscle of MA₁₀₀AL and MA₁₀₀R fish were higher than in the control, resulting in a higher protein‐accumulation rate and tissue growth. Total DNA content, indicated cell hyperplasia, was higher in MA₁₀₀AL and MA₁₀₀R than its respective controls. Studies of optical and electronic microscopy corroborated these results. These findings indicate that MA added to the diet can stimulate the growth, white‐muscle protein‐turnover rates and tissue hyperplasia in gilthead sea bream.     

Identifying mangrove areas for fisheries enhancement; population assessment in a patchy habitat

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