Agriculture Reference
In-Depth Information
14.2.1 Atlantic salmon
In a recent study, Dimitroglou et al . (2011b) evaluated the effect of dietary MOS (4g kg −1 )
on sea cage reared Atlantic salmon smolts (∼47 g) fed diets containing high levels of soy pro-
tein concentrate, extracted soy protein and sunflower meal in a 14 week experiment. Growth
performance parameters were not affected by MOS supplementation; however, body pro-
tein composition was significantly increased. Additionally, histological analyses revealed that
glycogen deposition in liver tissue increased in the MOS fed fish and the absorptive surface
area of the anterior intestine was increased. Scanning electron microscopy revealed that the
microvilli density was also significantly higher in the anterior intestine in the MOS fed fish
when compared to the control fed fish. Similar results were observed in the posterior intestinal
region using transmission electron microscopy, where microvilli length increased from 1.10
± 0.18 μm in the control group to 1.41 ± 0.19 μm in the MOS fed fish. Furthermore, the total
counts of sea lice ( Lepeophtheirus salmonis ) and salmon lice ( Caligus elongates ) attached
to fish, and total numbers of fish infected by lice, were significantly lower in the MOS fed
fish. At present it is not fully understood how dietary MOS supplementation can affect lice
infection, but it is hypothesized that it may relate to MOS induced mucus secretion on the fish
epidermis where a higher volume of mucus or altered mucus quality may prevent or retard lice
attachment. In any case, further research is warranted.
14.2.2 Brook trout ( Salvelinus fontinalis )
To the authors' knowledge only one prebiotic study has been published on brook trout (Sara
etal . 2010). Although no indication of statistical significance was indicated, from this 35 week
study it was reported that dietary inclusion of MOS (2 g kg −1 ) improved specific growth rate
(SGR), feed conversion ratio (FCR) and survival, reduced the percentage of neutrophils and
basophils, and increased the percentage of lymphocytes.
14.2.3 Rainbow trout
Staykov et al . (2005) reported higher growth gain and improved FCR of rainbow trout (∼30 g)
reared in net cages and raceways with the inclusion of dietary MOS (2 g kg −1 ). In addition, the
authors demonstrated increased serum lysozyme and complement activities of fish fed MOS
in net cages and raceways.
In a later study on rainbow trout (initial weight ∼14 g), Sealy et al . (2007) concluded that
inclusion of GroBiotic ® -A (a mixture of partially autolysed brewer's yeast, dairy ingredient
components and dried fermentation products) at 20 g kg −1 had no negative impacts on weight
gain, FCR, carcass composition, immune gene expression or non-specific immune responses.
However, dietary GroBiotic ® -A improved survival of fish after experimental challenge with
infectious haematopoietic necrosis virus. In contrast to this study, two studies on rainbow trout
(∼11 g) by Azari et al . (2011a; 2011b) reported that the inclusion of GroBiotic ® -A signifi-
cantly improved SGR, condition factor (CF) and protein efficiency ratio (PER). Furthermore,
the carcass protein level was significantly higher and the lipid content was significantly lower
in fish fed high levels (15, 20, 25 and 30 g kg −1 ) of GroBiotic ® -A. At the end of the 12 week
feeding trial the allochthonous gut microbiota was investigated. The aerobic bacterial levels
(g −1 ) were unaffected but a significant increase in the anaerobic and lactic acid bacteria (LAB)
levels were observed. Unfortunately, no further identification was carried out.
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