Prebiotics in Finfish: An Update - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 378

14.7 MORONIDAE
14.7.1 European sea bass
The European sea bass is the second most important fish species in the Mediterranean region
with an estimated production volume of over 70,000 tonnes in 2011 (FAO FIGIS 2013). To
our knowledge, MOS is the only prebiotic which has been tested on the European sea bass at
present (Table 14.5). The effect of two levels of MOS supplementation (2 and 4 g kg −1 )was
evaluated on European sea bass juveniles (35 g) ina9weekstudywhichshowedthatMOS
did not affect body proximate composition, fatty acid composition, growth parameters (except
SGR which was increased), blood serum alternative complement activity, lysozyme activity
or intestinal histology (Torrecillas et al . 2007). However, differences were reported in liver
lipid vacuolization and head kidney (HK) macrophage phagocytic activity. Furthermore, MOS
supplementation was able to improve disease resistance against enteric Vibrio alginolyticus
infection when fish were challenged by either cohabitation with infected fish or direct bacterial
inoculation of the gut. In the cohabitation trials, the presence of V.alginolyticus in sea bass HK
was 33% for the control group but only 8% and 0% for fish fed 2 and 4 g MOS kg −1 , respec-
tively. In the trials with direct gut inoculation with V . alginolyticus the number of infected
fish in the control group was double the level of the MOS groups within 48 h. Furthermore,
the number of the infected fish in the MOS groups remained the same at 24 and 48 h post
infection. A later trial, using multiple sub-experiments with European sea bass fed diets with
2, 4 and 6 g MOS kg −1 , revealed that MOS supplementation improved FCR, reduced hepatic
lipogenic enzymes activity, lowered hepatic lipid vacuolization and improved hepatocyte mor-
phology (Torrecillas et al . 2011a). Body proximate analysis revealed significant reduction in
crude lipids as well as moisture content. HK leukocyte phagocytic activity was also increased
in fish fed 4 and 6 g MOS kg −1 after 30, 45 and 60 days of feeding. In addition, intestinal
morphological analyses showed a dose-dependent enhancement in the number of the acid
mucin producing goblet cells, which may have been related to the improved bacterial resistance
observed in the previous study (Torrecillas et al . 2007) and in later studies whereby a signif-
icant reduction of intestinal V. anguillarum translocation, after in vivo and ex vivo exposures,
was observed in European sea bass (Torrecillas et al . 2011b; 2012; 2013). In addition Torrecil-
las et al . (2011b) observed improved intestinal morphology in the anterior intestine, posterior
intestine and rectum (fold height and surface area) as well as elevated acid mucin producing
goblet cells, higher infiltration of mixed leukocyte populations (mainly eosinophilic granulo-
cytes), and increased intestinal mucus lysozyme activity in MOS fed fish. Torrecillas et al .
(2012) reported that European sea bass fed 4 g MOS kg −1 displayed improved disease resis-
tance against Vibrio anguillarum and improved innate immune response and decreased stress
(confinement) induced changes on the posterior gut microbiota. In addition improved growth,
SGR and FCR were observed in MOS fed fish. More recently, Torrecillas et al . (2013) inves-
tigated the intestinal epithelial barrier health status of European sea bass fed 4 g MOS kg −1
in an 8 week study. Significant higher weight gain, total length, CF and SGR were reported
with MOS feeding. Furthermore, in the posterior intestine, prostaglandins production, choles-
terol/sterols, polar lipid fraction (due to phosphatidylethanolamine and phosphatidylcoline
increase), goblet cell levels and eosinophilic granulocyte levels increased with MOS feeding.
However, lipid class analysis of the posterior intestine revealed a reduction in the total neutral
lipid fraction, particularly due to a reduction in triacylglycerol content.