Prebiotics in Finfish: An Update - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 381

prebiotics have been tested in sea bream (Cerezuela et al . 2008; Dimitroglou et al . 2010a;
2011a; Gültepe et al . 2011; Tapia-Paniagua et al . 2011; Cerezuela et al . 2012; 2013a; 2013b)
(Table 14.6). Cerezuela et al . (2008) fed gilthead sea bream (∼175 g) two levels of inulin
inclusion, 5 and 10 g kg −1 , for both 1 and 2 weeks. The results showed a significant inhibition
of leukocyte phagocytosis and respiratory burst activities after 1 week but levels returned to
control levels at week 2. An in vitro study, where HK leukocytes were incubated with inulin,
showed no significant effects on leukocyte peroxidase, phagocytic, respiratory burst or natural
cytotoxic activities. Based on these findings, the authors suggested that gilthead sea bream
leukocytes do not have inulin receptors and inulin supplementation seems to be inappropriate
in gilthead sea bream rearing.
On the other hand, the use of MOS supplementation (2 and 4 g kg −1 ) in gilthead sea bream
(∼105 g) showed alterations of circulating leukocyte proportions as well as increased total
leukocyte levels within 2 weeks of feeding (Dimitroglou et al . unpublished data). Serum
lysozyme and alternative complement activity remained unaffected however. Microbial anal-
ysis revealed that MOS supplementation reduced the aerobic culturable intestinal microbial
load without altering the relative abundance of the identified bacterial species. A longer
nutrition study, supplementing MOS (2 and 4 g kg −1 ) into diets using either fishmeal (FM)
as the sole protein source, or partial replacement of FM with soybean meal (SBM), showed
that body proximate composition, growth parameters and feed conversion were unaffected by
MOS (Dimitroglou et al . 2010a). The hepatosomatic index (HSI) was significantly reduced
by the addition of MOS in diets where FM was the protein source. Histological evaluation
of liver showed no significant changes in glycogen deposition among experimental groups
but the posterior intestinal mucosal fold (villi) absorptive surface was significantly improved
by MOS in the fish fed the FM based diets. Electron microscopy revealed that dietary MOS
had a pronounced effect at the ultrastructural level, as microvilli density was increased with
MOS supplementation in both FM based and SBM based diets. Microbial analysis using
PCR-DGGE demonstrated that the effect of dietary MOS on the allochthonous microbial
populations was more distinctive in FM based diets, characterized by increased species
diversity, richness and reduced similarity, compared to the SBM fed fish, where species
diversity and richness remained unaffected and similarity between treatments was higher. It
was suggested that the presence of SBM oligosaccharides could have influenced the impact
of MOS on the intestinal microbial community.
In a 12 week feeding trial, Gültepe et al . (2011) investigated the effects of two levels (2 and
4gkg −1 ) of dietary MOS on the growth performance and digestive capacity of gilthead sea
bream (initial weight ∼170 g). The results showed that MOS significantly increased growth
performance, feed utilization and ADCs of protein and carbohydrate. However, no significant
effect was observed on lipid digestibility. Later, Gültepe et al . (2012) evaluated MOS (2 and
4gkg −1 ) supplementation on haematological parameters and histological evaluation of the
liver of gilthead sea bream. Administration of MOS did not affect the haematological param-
eters investigated (RBC, WBC, Thr, Ht, Hb, MCH, MCHC and MCV) and did not influence
liver histology. All samples displayed normal characteristics: homogeneous-sized hepatocytes
with slightly vacuolated cytoplasm and large, spherical, centrally located nuclei.
In a study with gilthead sea bream, Cerezuela et al . (2012) revealed that inclusion of 10 g
inulin kg −1 stimulated serum complement activity and phagocytic ability. However, these
effects were not observed at higher inclusion levels. Furthermore, inclusion of 10 g inulin kg −1
had no effect on the expression of immune-related genes in the head kidney (HK). A challenge