Probiotic Applications in Cold Water Fish Species - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 234

bathed in probiotic suspensions (∼10 7 cells ml -1 ) for 10 minutes, 7 days prior to the pathogen
challenge. The challenge was conducted by bathing salmon in suspensions containing 10 7 cells
ml -1 of A . salmonicida , V . anguillarum , Vibrio ordalii or Y . ruckeri for 10 minutes. The probi-
otic treatment led to a significant reduction in mortalities after challenge with A . salmonicida
(18% mortality in the probiotic treated fish versus 100% in the control). The probiotic effect
was less clear in the challenge studies using V . anguillarum and V . ordalii and no probiotic
effect was observed in the Y . ruckeri challenge where all of the probiotic treated and the con-
trol fish died. Gildberg et al . (1995) carried out a probiotic study on Atlantic salmon juveniles
where Lb . plantarum , later reclassified as Carnobacterium divergens , was incorporated into
feeds at 2.5 × 10 9 cells g -1 . The results of a cohabitation challenge with fish infected with
A . salmonicida revealed a clear tendency towards increased mortality of fish fed diets sup-
plemented with C . divergens . Prior to the challenge, C . divergens completely dominated the
culturable autochthonous gut microbiota of fish fed C . divergens ; however, in surviving fish
at the end of the challenge A . salmonicida outcompeted C . divergens as the population level
of LAB (presumed C . divergens ) was reduced. In contrast to the lack of protecting effect of
C . divergens reported by Gildberg et al . (1995), Robertson et al . (2000) reported a protective
effect of Carnobacterium inhibens , isolated from the GI tract of Atlantic salmon (Jöborn et al .
1999), towards A . salmonicida , V . ordalii and Y . ruckeri challenges. However, C. inhibens was
not effective against V . anguillarum .
The European Union has imposed restrictions on scientists in the use of experimental ani-
mals including fish in in vivo studies (Revision of the EU Directive for the Protection of
Animals Used for Scientific Purposes, Directive 86/609/EEC, 8 September 2010) and, in light
of this imposition, in vitro and ex vivo methods have been suggested as alternatives. With
regards to ex vivo methods, three papers have used an intestinal sac method to evaluate adher-
ence of probiotics in the GI tract of Atlantic salmon (Ringø et al . 2007a; Salinas et al . 2008;
Kristiansen etal . 2011). Ringø etal . (2007a) and Salinas etal . (2008) evaluated the interactions
between LAB ( C . divergens and Lb . delbrueckii subsp. lactis , respectively) and pathogens in
the intestine and concluded that the LAB used was able to outcompete the pathogen to some
extent. In a more recent study, Kristiansen etal . (2011) showed that C . divergens adhered to the
epithelium or mucus in the proximal intestine of Atlantic salmon but this effect was not appar-
ent in the distal part of the intestine. However, by using this method one should bear in mind
that the method is restricted to short term experiments as the viability of intestinal tissue is
limited once it is excised from the host and permanent adherence merits further investigations.
9.3 GADIDAE
9.3.1 Atlantic cod ( Gadus morhua )
Atlantic cod is an important economic commodity in international markets, and declining
stocks over the last decades have motivated the commercial development of cod aquacul-
ture, mainly in Norway but also in the UK, Iceland and Canada to some extent (Lauzon
2010). However, biological and technological constraints have hampered the expansion of
cod culture (FAO 2009; Rana 2007). Health and disease management at early cod stages has
relied on the use of antibiotics since vaccination is first conducted on 1 g juveniles (Lauzon
2010). The need for faster growing and healthy juveniles has prompted the search for novel
prophylactic methods.