Merrifield, D., Dimitroglou, A., Bradley, G., Baker, R. T. M., & Davies, S. J. (2010) Probiotic applications for rainbow trout (Oncorhynchus mykiss Walbaum) I. Effects on growth performance, feed utilisation, intestinal microbiota and related health criteria. Aquaculture Nutrition, 16, 504-510.
Over the years many pathogens have caused large losses in aquacultural fish stocks; with the gastrointestinal tract suggested as the main source of entry for many fish pathogens. This has created the idea for probiotic use in combating these pathogens, by strengthening the defensive barrier of the indigenous gut microbiota. As well as helping control disease, probiotics have been shown to contribute to digestive function, have been implicated in development/maturation of gut and immune systems and have been shown to promote growth. These properties have been demonstrated in fish including trout, with a majority of probiotic interest being focused on lactic acid bacteria (LAB) and Bacillus species. However, although several studies have shown health promoting properties relating to the use of probiotics, there is a lack of information concerning beneficial effects on juvenile rainbow trout. Therefore the aim of this study was to investigate the effects of three probiotic species: Enterococcus faecium, Bacillus subtilis and Bacillus licheniformis, on juvenile rainbow trout growth, performance, feed utilisation, intestinal colonisation and related health parameters.
In this study the fish were fed a selection of the three probiotic species, either E. Faecium (EF), B. subtilis and B. licheniformis (2B) or all three of the above (EF + 2B). The fish were fed equal diets and the aquarium water was changed regularly. At the end of the trial three fish per tank were euthanized and their intestines were removed, homogenised and plated onto duplicated agar plates. Furthermore, blood was taken from three fish from each tank to measure the volume percentage of red blood cells (haematocrit levels) and the number of leukocytes present. The results showed efficient utilisation of feed in all treatment groups with an increase in fish biomass by 300%. B. subtilis and B. licheniformis were shown to be more effective in enhancing growth and body composition of rainbow trout and were not found in the control fish. However, high levels of all three probiotic species were found in respective samples. Haematocrit levels were found not to have changed throughout the probiotic treatments; although a significant increase was found in leukocyte numbers from group 2B + EF, whereas no change was found in the groups fed Bacillus spp. or E. faecium separately.
The current study was successful in demonstrating the ability of all probiotic species to survive transit through the digestive tract and colonise the intestine of rainbow trout. It also shows the potential benefits of probiotic utilisation in aquaculture. I believe the future prospects of probiotic use to be highly beneficial, especially as an alternative to antibiotic use. I believe this is also supported by previous studies indicated that the presence of E. Faecium resulting in the reduction of intestinal microbiota such as E.coli, Staphylococcus aureus and Clostridium spp. However, I agree with the authors that further research should be carried out in this area to help understand the full extent of benefits associated with probiotic use.
3 comments:
it is a shame this study did not perform the experiment on juveniles and adult rainbow trout to actually see if the age made a difference! it is generally accepted that the addition of probiotics to a gut that has already developed a microbial community is unlikely to have lasting effects and therfore probiotics should be added when the fish have just hatched.
Yeah maybe it could have been beneficial, however I think they didn't because they said that a lot of research has been carried out on that already and maybe it would have been a waste of time. especially if what you say is true about the probiotics not working on adult fish, although in the end I guess that is just another variable which they didn't want to investigate.
yes i suppose but i dont know of any experiments that have actually made the direct comparison in the same study and therefore confirmed any difference between adult and juvenile. An experiment that looked at how long the pronbiotics remained in the gut after treatment in adult compared to juveniles would be good, shame the dissertations are done now :)
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