Probiotic Applications in Cold Water Fish Species - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 235

Applications of potential probiotics in cod rearing have been beneficial in many different
ways (Table 9.3). Microbiota control and changes in its composition have resulted following
probiotic treatments at larval and juvenile stages. Addition of an autochthonous LAB strain
(initially identified as Lb. plantarum , but later reclassified as Carnobacterium divergens )into
the rearing water of 5 days post hatching (dph) cod larvae at an initial dose of 10 5 colony
forming units (CFU) ml -1 influenced the gut bacterial composition and resulted in strain col-
onization, accounting for 70% of the cultivable microbiota (9 days post-treatment), as well as
the reduction of opportunistic bacteria (Strøm and Ringø 1993).
At early larval stages, the GI tract is poorly developed. The microbiota established may
therefore reflect that of the environment and live feed which often carries high bacterial load
(Olafsen 2001; Chapter 16 ). Hence, early and frequent probiotic treatments should be applied
for maximum effect. The regular addition of two bacterial strains ( Arthrobacter sp. and Entero-
coccus sp.) via rearing water (10 5-7 CFU ml -1 ) from early post-fertilization of cod through the
larval stage contributed to gut microbiota control and lower Vibrio levels, as well as enhanced
larval survival, growth, development and vitality (Lauzon et al . 2010a; 2010b; 2010c). Indeed,
enhancement of the gut microbiota in the probiotic-treated groups (36 dph) was suggested to
have played a role in better feed utilization of cod larvae, enabling their faster weight gain
despite the same feeding ration given to all groups. The presence of the potential probiotics in
cod larval gut was confirmed 8 days post-treatment (Lauzon et al . 2010c). Further, the prop-
erties of the two prospective probiotics, isolated at the cod hatchery, were confirmed in an
intervention study of early cod juveniles (Lauzon et al. 2010d). Dry feed coated with sin-
gle or mixed probiotics was administered for 54 or 27 days, respectively. Microbiological
stability of the probiotics added to the feed was demonstrated. Juveniles administered the
Enterococcus -probiotic feed grew faster and had lower gut Vibrio loads than control juveniles.
Overall, the results suggest that both probiotics, especially the Enterococcus strain, modified
the gut microbiota and contributed to enhanced juvenile growth and survival. During a larval
study involving the application of a commercial product (Remus ® , Avecom), via supplemen-
tation of rearing water and enriched rotifers, up-regulation of proteins related to growth and
development as well as down-regulation of stress-related proteins were detected in cod larvae
(Sveinsdottir et al . 2009).
Cod juvenile trials dealing with administration of probiotics via feeding were initiated more
than a decade ago and aimed mainly at assessing their disease reducing potential. Gildberg
et al . (1997) investigated the effect of C. divergens administered to Atlantic cod juveniles via
feeding (10 7-9 CFU g -1 ) for six weeks, and reported some protection upon challenging with
V. anguillarum at the midterm and observed C. divergens among the intestinal microbiota
of surviving fish. A similar feeding experiment conducted for three weeks by Gildberg and
Mikkelsen (1998) showed a significantly reduced cumulative mortality 12 days post-challenge
while the effect was lost 4 weeks post-infection. Nevertheless, colonization of the probiotic in
the cod intestine was again observed.
More recently, the emphasis has been towards the elucidation of the different properties
of probiotic strains. The ex vivo study of Martinsen et al . (2011) indicated the modulating
effect of an autochthonous probiotic strain of Carnobacterium maltaromaticum on the cod
midgut microbiota following exposure (10 7 CFU ml -1 ) for 30-60 min, as well as its abil-
ity to outcompete V. anguillarum .The in vitro study of D'Alvise et al. (2012) showed the
ability of Phaeobacter gallaeciensis BS107 (10 7 CFU ml -1 ), a producer of the antibacterial
compound tropodithietic acid (TDA), to reduce cod larval mortality in challenge trials with