The role of exopolymers in hatcheries: an overlooked factor in hatchery hygiene and feed quality

Extracellular Polymeric Substances (EPS),1 or exopolymers, play vital roles in the productivity of commercial hatcheries, yet have received little attention in aquaculture outside of their role in the biofilters of recirculating systems. Hatcheries have long dealt with EPS in microalgal cultures or larval rearing systems when quantities manifest themselves visually as biofilms or mucilaginous aggregates. The same polymers in lesser, visually undetectable quantities have the ability to attract commensal bacteria and sequester micronutrients, which can be essential in hatcheries for hygiene, stability of rearing environments, and the production of microalgae for live feeds. EPS may also serve an important role in nutrition both directly in the particle selection of filter feeders, and indirectly through their contribution to microflora in the larval gut of both fish and invertebrates. EPS have been well-studied in marine ecosystems, but their presence in hatcheries has until recently been largely overlooked, perhaps on account of their invisibility using normal microscopy and their extremely small size, both factors which may explain why they are sometimes also referred to as transparent exopolymeric substances (TEPs). This review examines recent literature for ways in which EPS affect hatchery processes, with suggestions as to how further research and development of biosensor technologies for EPS have the potential to improve production processes.