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 resources 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.
2011: Progress and activities:
The project has been running for almost a year now, and the first months have
included a kick-off meeting with all project participants as well as the appoint-
ment of a post doc. All work packages in the project are based on sampling during
feed experiments with rainbow trout fry. A large feed experiment is currently
running. Four trout fry diet codes are investigated, one conventional diet code
with and without probiotic and one organic diet code with and without probiotic.
The probiotic used is commercially available and is licensed for adding to fish diets.
During the experiment samplings aiming on molecular as well as traditional
bacteriological studies have been done regularly (among them a null point sampling
before feeding of the fry had begun), focusing on the intestine. Samples of
inner organs have also been taken for use in traditional bacteriological as well as
immunological studies. At fry sizes 1 g and 4 g experimental infection studies using
the fish pathogens Flavobacterium psychrophilum and Yersinia ruckeri, respectively, have been done with minor groups of fry that have been feed the different diet codes. The bacteriological investigations have been performed during
the experiment, while the other investigations (among them the molecular and
immunological studies) will be done, when the sampling has been finished. When
all studies are summarized, it will be possible to clarify if there are differences in
survival rates of trout fed either organic or conventional diet, and if the investigated organic diet code as well as the addition of probiotics will result in a healthier rainbow trout fry. The result will also give an indication on how to set up the next feed experiment.
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