Abstract
SummaryThe expanding aquaculture industry plays an important role in feeding the growing human population and with the expansion, sustainable bacterial disease control, such as probiotics, becomes increasingly important. Tropodithietic acid (TDA)‐producing Phaeobacter spp. can protect live feed, for example rotifers and Artemia as well as larvae of turbot and cod against pathogenic vibrios. Here, we show that the emerging live feed, copepods, is unaffected by colonization of the fish pathogen Vibrio anguillarum, making them potential infection vectors. However, TDA‐producing Phaeobacter inhibens was able to significantly inhibit V. anguillarum in non‐axenic cultures of copepod Acartia tonsa and the copepod feed Rhodomonas salina. Vibrio grew to 106 CFU ml−1 and 107 CFU ml−1 in copepod and R. salina cultures, respectively. However, vibrio counts remained at the inoculum level (104 CFU ml−1) when P. inhibens was also added. We further developed a semi‐strain‐specific qPCR for V. anguillarum to detect and quantify the pathogen in non‐axenic systems. In conclusion, P. inhibens efficiently inhibits the fish larval pathogen V. anguillarum in the emerging live feed, copepods, supporting its use as a probiotic in aquaculture. Furthermore, qPCR provides an effective method for detecting vibrio pathogens in complex non‐axenic live feed systems.
Highlights
Aquaculture provides high-quality protein for approximately three billion people worldwide and with the estimated increase in the human population combined with overfishing, this number is likely to increase (WWF and ZSL, 2015; FAO, 2016)
We show that the emerging live feed, copepods, is unaffected by colonization of the fish pathogen Vibrio anguillarum, making them potential infection vectors
Vibrio grew to CFU mlÀ1 and CFU mlÀ1 in copepod and R. salina cultures, respectively
Summary
Aquaculture provides high-quality protein for approximately three billion people worldwide and with the estimated increase in the human population combined with overfishing, this number is likely to increase (WWF and ZSL, 2015; FAO, 2016). Larvae of several commercially important species including cod, halibut and turbot are fed using live feed due to the lack of suited artificial feed formulations. Marine fish larvae have been fed using rotifers and Artemia, copepods are more representative of the natural diet (Turner, 2004). Copepods have several advantages over traditional aquaculture live feed including desirable amino acid profiles, a high fatty acid content and swimming patterns that promote feeding in fish larvae (Støttrup et al, 1986; Støttrup and Norsker, 1997; Bell et al, 2003; Turingan et al, 2007). Substituting rotifers with copepods (Acartia tonsa) in the initial larval feeding stage has a long-term positive effect on survival, growth and viability of Atlantic cod and ballan wrasse fish larvae (Øie et al, 2017). The use of copepods as live feed in larval rearing has not been cost-effective; new approaches to copepod breeding are improving the cost balance (Abate et al, 2016), making copepods a relevant live feed in commercial aquaculture
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