The study was published in Aquaculture Reports.
Researchers from the University of Queensland and Ridley Aqua Feeds, decided to investigate whether substitution of marine ingredients with alternative protein inputs to reduce reliance on capture fisheries affects gut microbiome and resilience to environmental stress in black tiger prawns.
The study set-up
The team conducted a replicated, randomized, blind feed trial in juvenile P. monodon.
To investigate replacement protein sources in feeds for the prawns, they tested three isonitrogenous, isoenergetic diets, incorporating fisheries by-product meal, cattle and poultry by-product meal and soybean meal as the major protein.
Juvenile P. monodon were acclimatized to a reference diet for two weeks, weighed, then fed the experimental diets for two weeks.
Elevated temperature, pH and salinity was applied for a subsequent 14 days, explained the team.
To determine any effect of diet on intestinal microbiome the V6-V8 region of the 16s rRNA gene was sequenced on arrival from the farm, at the end of acclimatization period, 24 hours following the introduction of the test feeds, immediately after the two week test feed period and subsequent to the prawns being exposed to the stressful conditions.
Results
The experts saw that feed conversion ratio was significantly higher in animals fed a soybean meal-based diet.
But they found no significant effect of diet on alpha diversity of the midgut microbiota, and no correlation between stress resilience, diet and gut microbiome diversity.
“We found rapid change in microbiome diversity after a single feed on a new diet, but no correlation between intestinal bacteria diversity and protein source was made after feeding for two weeks or through the stress period.
“Our experiment showed that changes in the protein source used to formulate the feed did not significantly affect the intestinal microbiome in terms of composition and diversity, provided that the diet continues to be well-utilized by the animals.”
What they did observe, though, was that time had a significant impact on beta diversity throughout the experiment, across all three diets.
They saw that the most abundant genera on arrival from the farm were from the genera Photobacterium and Vibrio. The relative abundance of members of the Rhodobacteraceae, Pseudoalteromonadaceae, Mycoplasmataceae and Flavobacteriaceae families increased throughout the trial and were also found in the seawater supply, they reported.
Conclusions
The researchers concluded that changing only the protein in the diet is not sufficient to impact gut microbiome, even when animal growth and feed conversion is severely compromised by the diet.
“We found that time/age are the major drivers of intestinal microbiome changes in black tiger prawn with diversity increasing as the animal ages.”