Aquatic bacterial communities: Forces and dynamics behind their formation and impact in embryo and larval culture.

Abstract

The majority of successful aquaculture has come from a relatively small number of species; however, still many economical important species remain underdeveloped. In particular, egg hatching and survival of larvae have proven to be bottlenecks to the complete and sustainable aquaculture of many species. The European eel is one such yet underdeveloped species, both as human food source and as object needing conservations measures after a dramatic decline in glass-eels (juveniles) over the last 40 years (Dekker, 2008). During their early life stages in the wild, they are exposed to oceanic environments low in microbial activity (Sjöstedt et al., 2014) while in aquaculture, they are vulnerable to bacterial infections (Sørensen et al., 2014) due to an immature adaptive immune system (Suzuki et al., 2000; Swain et al., 2009) well known especially for marine fish larvae (Hansen & Olafsen 1999). A stable and healthy microbial community within these aquaculture systems is therefore a prerequisite for a suitable European eel production environment. Eel therefore provide an excellent model for investigating the effects of microbial communities on fish egg hatching and larval survival. Aquaculture microbial community is significantly stabilized utilizing RAS technology (Recirculating Aquaculture Systems) (Attramadal et al. 2013). RAS enable stable microbial systems over time, by the constant feedback of nutrients released from organisms providing a selection and stabilization force of the microbial community (Attramadal et al. 2013). Although a well-balanced community is known to be of pivotal importance for the system, little is known regarding the forces that drive stability and how to reach a healthy state (Blancheton et al., 2013). By using microbiological and chemical analysis techniques, we compare pelagic eel embryonic and larval bacterial communities in response to water cleaning treatments such as ultrafiltration (500kd), UV and ozonation as well as biological maturation to create different types of aquatic environments. The aim is to understand the dynamics of aquatic microbial communities and the forces that drive them. This knowledge is of pivotal importance to enhance offspring survival during the early life stages of sensitive marine fish species. Using the European eel as a model species, we utilize state-of-the-art chemical and microbiological techniques, to endeavour scientific adaptability of complex aquatic microbial communities and aim ultimately to improve sustainability of aquaculture.