Cod larvae. (Photo: Nofima)
Scientists find new way to protect cod from vibriosis pathogen
Friday, August 24, 2012, 15:20 (GMT + 9)
A new study shows that Phaeobacter gallaeciensis is harmless and beneficial for the early life stages of cod. In this sense, it concluded that it is a promising probiont in marine larviculture and that tropodithietic acid (TDA) production likely contributes to its probiotic effect.
The study, called 'Phaeobacter gallaeciensis Reduces Vibrio anguillarum in Cultures of Microalgae and Rotifers, and Prevents Vibriosis in Cod Larvae,' was published in the latest issue of the journal PLOS ONE.
The study demonstrates that Phaeobacter gallaeciensis is good for the early life stages of cod and also that it is highly efficient at preventing infections with the fish pathogen V. anguillarum. The probiotic effect can be achieved at the low temperature (7°C) used for the cod embryos and yolk sac larvae.
Based on these findings, researchers hypothesize that P. gallaeciensis can be used in marine larviculture to control the ambient, potentially harmful microbiota in cultures of rotifers and microalgae and against vibriosis in fish larvae.
Previous studies showed that a Phaeobacter sp. can protect turbot larvae against vibriosis at higher temperatures (18°C). Non-infected larvae showed some level of initial mortality, which may have been due to opportunistic bacteria introduced with the embryos.
Both challenged and unchallenged cod larvae exposed to P. gallaeciensis had a significantly lower initial mortality, indicating that P. gallaeciensis may control the inherently occurring microbiota.
The present study takes a system approach to preventing bacterial disease in aquaculture animals, aiming at microbial control throughout the environment of the fish and the lower levels of the production.
Scientists determined that cultures of two aquaculture-relevant algae and of the rotifer B. plicatilis can be colonized by P. gallaeciensis without compromising their growth, and that P. gallaeciensis will strongly reduce or eliminate the pathogen V. anguillarum.
Therefore, the authors of the study stated that introducing P. gallaeciensis at this level is thus very promising, since live feed is a common source of pathogens. These findings corroborate the hypothesis from a previous study that algae and rotifers in aquaculture can be grown together with probiotic Roseobacters to prevent the proliferation of disease.
Further, using probiotic bacteria offers the advantage that nutrients are consumed, niches are occupied and the rapid re-growth of pathogens is prevented.
By Natalia Real