A group of international researchers have examined the use of a commercial yeast-based feed additive in the production of rainbow trout as a way to improve fish health and production. The team reported the results in the journal Aquaculture Research.
They evaluated yeast-based probiotic, composed of Saccharomyces cerevisiae and Saccharomyces elipsoedas, on health and performance of rainbow trout, looking at its effects on intestinal microbiota, immunity and rainbow trout growth performance.
“The beneﬁts from this yeast-based probiotic include the modulation of intestinal microbiota, enhancement of immune responses, particularly the inhibitory potential of skin mucus against ﬁsh pathogens, contribution to intestinal enzymatic physiology and last, improvement of growth performance,” they said. “These beneﬁcial features afﬁrm the importance of probiotics in improving ﬁsh health and performance, and concomitantly advance the prospective of yeasts as a microbial group for probiotics application in aquaculture, which is presently dominated by bacterial probiotics.”
The group also found that there were no palatability challenges with the yeast supplement.
Aquaculture has rapidly expanded in the last decades, making the sector one of the major players in the global food production, according to the UN's FAO. Along with this development is a challenge of producing farmed fish using sustainable and efﬁcient technologies, said the researchers. "A strategy in modern aquaculture to combat production bottlenecks associated with intensiﬁcation is preventive health care (Kiron 2012) through the use of consumer and environment-friendly alternatives such as vaccines, immunostimulants, prebiotics and, most importantly, probiotics (Lazado & Caipang 2014)."
Rainbow trout (Oncorhynchus mykiss) is farmed in Europe, North America, Chile, Japan, Australia and some parts of Asia including Iran. Several studies have shown that probiotics are viable alternatives in improving the health status of that fish, said the team.
The influence of probiotics to host microbiota is an area of great interest currently, noted the authors in the paper. "There is considerable evidence in the importance of host microbiota to fish immunity and metabolism, hence the beneficial actions of probiotics particularly their capability in modulating the population of these beneficial microorganisms is considered an advantage (Gomez & Balc azar 2008; Merrifield, Dimitroglou, Foey, Davies, Baker, Bøgwald, Castex & Ringø 2010)."
And yeasts, they continued, are a microbial group said to have immense promise as probiotics in aquaculture (Navarrete & Tovar-Ramırez 2014).
Some work has already been done examining the use of yeast products in fish, they said. Much of that work has focused on Saccharomyces cerevisiae and halotolerant Debaryomyces hansenii.
"It is interesting to highlight, however, that over 90% of the probiotic studies in rainbow trout employed bacterial probiotics and the use of yeast [has] received scant attention,” said researchers.
In the experiment, a yeast-based feed additive - the commercially available, Aqualase, comprising mainly S. cerevisiae and S. elipsoedas - was included at varying levels in fish diets for a period of eight weeks, said the researchers. Fish had a two-week acclimation period and were fed three times daily.
After acclimation, 360 fish were separated into 12 tanks of 30 fish, they said.
Diets included a control group getting the basal diet and 1%, 1.5% and 2% of the yeast treatment.
Skin mucus was collected a midpoint and end of the experiment. It was checked for protein concentration, alkaline phosphatase and lysozyme activity and inhibition against four pathogens.
Additionally, blood samples and fish intestines were taken, said the researchers.
Growth performance indicators, including weight gain, specific growth rate, feed conversion ratio and survival rate, were determined at the end of the experiment, they said.
Fish getting the highest level of yeast additive had an improved aerobic bacterial count and all fish getting the supplement saw a boost in intestinal lactic acid bacteria, said the researchers.
“Digestive physiology was affected by in-feed probiotics through improvement of intestinal enzyme activities,” they said.
The team found fish getting the supplement also had increased levels of protein, lysozyme and pathogen inhibition in their skin mucus. “Inhibitory potential was enhanced by around 50% compared with control when the ﬁsh were fed with probiotics especially at inclusion levels higher than 1%,” they added.
Fish getting 1.5% and 2% of the additive in their diets had improved growth performance in several areas including weight gain, and specific growth rate, said the researchers. Performance metrics in those areas increased linearly with the amount of supplement.
“Feed conversion ratio was enhanced signiﬁcantly in groups that received probiotics at 1.5% and 2% in the diet,” they said. “Survival rate ranged 92–97% in all experimental groups, and no signiﬁcant differences were noted between treatments.”
Body composition was not altered with the treatment, noted the team.
Source: Aquaculture Research
Title: Aqualase, a yeast-based in-feed probiotic, modulates intestinal microbiota, immunity and growth of rainbow trout Oncorhynchus mykiss
Published online ahead of print: DOI: doi:10.1111/are.13019
Authors: M. Adel, C. Lazado, R. Safari, S. Yeganeh, M.J. Zorriehzahra