Intensive aquaculture productie in multistakeholder environment (KB-12-001.01-006)

Ragworms (Nereis virens) are a rich source of high quality protein and polyunsaturated fatty acids.  They are suspected to contain special bioactive compounds including antimicrobial agents with positive effects on the gut microflora and health of fish fed ragworms.  Previous studies conducted at IMARES have shown better growth, increase in hematocrit and haemoglobin levels and  in sole fed ragworms compared to commercial diets (Kals et al., submitted).  To test the effect of ragworm on fish gut health, several experiments were conducted both in vivo and in vitro to study the effects of ragworms on fish growth, physiology, gut and system microbial composition.

 

The first studies have demonstrated that ragworms contain mainly four bacteria types: Shewanella sp, Vibrio sp  (no Vibrio vulnificus), Flavobacterium sp and Acinetobacter sp / lwoffi.  Nevertheless, the whole worm homogenate, its mucus and faeces do not inhibit the growth of pathogenic Vibrio’s (V. vulnificus en V. anguillarum) in vitro.

 

To test whether the form of iron has an effect of the prevalence of pathogenic vibrio’s, the growth of 3 vibrio species was investigated in vitro in basal broth and basal agar supplemented with inorganic and organic form of iron.  V. vulnificus, V. scophthalmi and V. fisheri grow faster in organic source of iron than in inorganic form of iron.  The gowth in later media was comparable to that in basal iron-free culture media (control).

 

The effect of different iron concentrations in diet on the growth of (pathogenic) bacteria in sole guts has been further investigated in vivo in sole fed commercial diets and diets with different concentration of inorganic iron.  Gut homogenates are being processed using high throughput sequencing techniques to characterise the gut microbial community composition in sole. Data is expected to be available at end of January 2014.

The results will be introduced into a PPS-project or used for a direct industrial funded project.