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.

2013: Progress and activities:

The aim of OPTIFISH is to optimize growth and survival for organic cultured rainbow trout, the domi-nant fish species produced in Denmark. A minor part of the rainbow trout is produced as organic fish. Until 2013, there has been no production of organic fry but only production of organic trout from the size 25 g and onwards. The reason for that is that the classification organic only can be given to fish that have been treated with antibiotics up to a certain number of times in a lifetime. This is hard to achieve as recurrent disease outbreaks, especially with the bacterium Flavobacterium psychrophi-lum, 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 nutri-ents, 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. OPTIFISH has since project start become even more relevant for the aquaculture industry, as the EU regulation EEC 710/2009 is claiming organic fish to be organically produced since day 1 (and not first from size 25 g as it currently is for trout), as from January 1st 2016 the latest, with a gradually transition from the current situation to the 100 % organic status.

OPTIFISH has been focused on diet experiments with rainbow trout fry. All investigations have been depending on sampling in connection with those diet experiments.

The first diet experiment where four diets (a commercial available diet with and without probiotics as well as an organic diet with and without probiotics) were investigated has been finished. The used probiotic is commercially available (Bactocell®) as well as approved as an additive for fish diets. In the organic diets fish oil was exchanged with rape seed oil, and pea protein was added, in comparison with the commercial available diet. During the experiment regular sampling was done (including a sampling before first-feeding) for molecular and immunological studies as well as traditional bacteriological examination, focusing on the intestine. Additionally, sampling of inner organs for traditional bacteriology as well as potential immunological studies was done. At fry sizes 1 g and 4 g (50 and 92 days after first feeding, respectively), minor groups of fish from the different diet groups were experimentally infected with Flavobacterium psychrophilum and Yersinia ruckeri, respectively.

Both are well recognized pathogens in rainbow trout fry. Mortalities were registered and sampling for traditional bacteriology as well as molecular microbiology and immunology were continued during the infection experiments. The results of the laboratory analyzes showed that the intestine was colonized by bacteria before first-feeding, but the amount of bacteria increased significantly in connection with first-feeding. A chance in the composition of the bacteria was seen in connection with feeding. There did not seem to be a difference in the groups depending on the addition of probiotics to the feed but it seemed to be depending on the fish having had either the conventional or the organic diet. The immunological analyses showed the same result. The experimental infection studies showed no difference in mortalities between the diet groups, but the molecular analyses (qPCR) showed a lower amount of pathogenic bacteria in the intestine of fish fed the organic diets.

In summing up the results of this diet study it seemed that there was advantages connected to the investigated organic diet, but as several diet factors were different (both oil and protein contents) between the organic and conventional diets, it was not possible to pinpoint precisely which diet factor that caused this. Therefore, it was decided to focus the second diet study on 5 diet types (4 organic diets where only one ingredient was changed between the diets and 1 conventional diet (same diet as in first diet study). One of the organic diets was an organic version of the conventional diet, whereas as the other three diets had rape seed oil instead of marine fish oil, added pea protein, and both rape seed oil and pea protein, respectively, the last diet being the same as the organic diet evaluated in the first diet experiment.

Again regular sampling was done during the experiment. Experimental infection challenges were done on small groups of the fish, Flavobacterium psychrophilum at day 110 after first feeding (average fish weight 1 g) and Yersinia ruckeri at day 160 after first feeding (average fish weight 4 g). Overall there were no differences in survival between the groups of fish after the challenges with either F. psychrophilum or Y. ruckeri. Samples were taken of fish intestines, water and the diets for sequencing analyses, as well as samples of fish intestines for gene expression studies and histology and samples for traditional bacteriology.

Currently, samples are still being processed, but at this stage most of the sequencing results are available. It seems that the diet type has a high influence on the bacterial flora in the fish intestines, and it seems to be the pea protein that is the reason for the changes.

When all results are summarized it is expected that it will be elucidated if there are differences in survival among fry after being fed diets of either organic or conventional origin, and it will show if any of the organic diets investigated results in a more healthy rainbow trout fry. It will also be elucidated, if the OPTIFISH project results can lead to a more 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.

2012: Progress and activities:

OPTIFISH is more than halfway through the project period and is focusing on diet experiments with rainbow trout fry. All investigations in the different working packages of the project are depending on sampling in connection with those diet experiments. The first diet experiment where four diets (a commercial available
diet with and without probiotics as well as an organic diet with and without probiotics) were investigated has been finished. The used probiotic is commercially available as well as approved as an additive for fish diets.

During the experiment regular sampling was done (including a sampling before first-feeding) for molecular
and immunological studies as well as traditional bacteriological examination, focusing on the intestine. Additionally, sampling of inner organs for traditional bacteriology as well as possible immunological studies was done. At fry sizes 1 g and 4 g, minor groups of fish from the different diet groups were experimentally
infected with Flavobacterium psychrophilum and Yersinia ruckeri, respectively.

Both are well recognized pathogens in rainbow trout fry. Mortalities were registered and sampling for traditional bacteriology as well as molecular microbiology and immunology were continued during the infection experiments. The diet experiment was terminated primo 2012. Thereafter the laboratory analyses on the samples have been done. The results from the experiment have shown that the intestine is colonized by bacteria before first-feeding, but the amount of bacteria increases significantly in connection with first-feeding. A chance in the composition of the bacteria was seen in connection with feeding. It did not seem that there was a difference in the groups depending on the addition of probiotics to the feed but it seemed to be depending on the fish having had either the conventional or the organic diet. The immunological analyses showed the same result. The experimental infection studies showed no difference in mortalities between the diet groups, but the immunological analyses showed a lower amount of pathogenic bacteria in the intestine of fish fed the organic diets.

In summing up the results of this diet study it seems that there might be advantages connected to the investigated organic diet, but as several diet factors were different (both oil and protein) between the organic and conventional diets, it was not possible to pinpoint precisely which diet factor that caused this. Therefore, it was decided to focus the second diet study (started up November 2012) on 5 diet types (4 organic diets where only one ingredient was changed between the diets) and 1 conventional diet (same diet as in first diet study)). Again regular sampling will be done during the experiment. When all results are summarized it is expected that it will be elucidated if there are differences in survival among fry after being fed diets of either organic or conventional origin, also after infection, and it will show if any of the organic diets investigated results in a more healthy rainbow trout fry.

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 appointment 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.

Project leader

Lone Madsen
Danmarks Tekniske Universitet
Bülowsvej 27
1870 Frederiksberg C

Tel: (+45) 35 88 68 26
E-mail:loma@vet.dtu.dk

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Find publications from the project in Organic Eprints