Influence of probiotics and feed on organic rainbow trout health

The aim of OPTIFISH is to optimize growth and survival for organic cultured rainbow trout, the
dominant fish species produced in Denmark. A minor part of the rainbow trout is produced as
organic fish. Currently there is no production of organic fry, as the classification organic only can be
given to fish that have been treated with antibiotics no more than twice in a lifetime. This is hard to
achieve as recurrent disease outbreaks, especially with the bacterium Flavobacterium psychrophilum,
are seen during the fry stage. A further challenge known from salmon culture is that diets with high
plant contents cause enteritis and injury to the intestine, which will affect the absorption of nutrients,
affecting the overall health status and welfare of the fish. The result is a higher risk of disease
following exposure to pathogenic microorganisms. OPTIFISH will investigate how organic diet types
with varying amounts of fish and plant sources as well as with or without probiotics (lactic acid
bacteria) will affect the intestine, the intestinal microbial flora and survival rates of rainbow trout
following exposure to pathogens. The use of probiotics for fry are assumed to result in a higher health
level. The overall result will be a sustainable production with an optimal utilization of the available
organic ressources as well as the scope for the industry that they by using the optimal diet type will
achieve a robust and healthy fish, something that can be achieved not only in organic but also in
traditional farming. A robust and disease-free fry is the most important factor for a higher production
in organic aquaculture in the future.