What's for Dinner Mum? Microbial Fish Soup.

Through excessive demand on sea food with population growth, aquaculture has become a necessity for the sustainability of the seafood industry. Fish farming must be maintained at a high level of maintenance, however even with safety measures and precautions set up farmed fish are still easily subjected to pathogens. This research was undertaken to gain a better understanding of the gut microbial composition. This study will provide a good foundation for further analysis on the health of farmed fish as well as other forms of aquaculture. It will also allow us to determine the most dominate phylum of bacteria found within a fishes digestive system and allow for better detection of potential pathogens.

3 common species of commonly used cage fish were chosen for this analysis, Cobia, Pompano and Milkfish. Each fish was reared and kept on a specific diet for the purpose of understanding gut microbiota and how this can differ between species with similar/dissimilar diets. Each species was reared in fish cages for a month and fed a slow sinking pellet for the first 40 days, twice a day. Once fish had reached a certain weight (around 30g) they were moved into different (HDPE) tanks, this also meant a change to the type of diet each fish had.

Cobia were kept on a diet of low-priced sardines whereas the milkfish and pompano were fed 9–13mm commercial pellet which was made of 40% crude protein 15% crude fat, 9% ash, 2.4% crude fibre. This was kept up for 8 months before 5 fish of each species were taken for microbial analysis. Fish were euthanized, and gut samples were taken from the lower intestine of each fish for analysis, the DNA was extracted via the use of DNeasy blood and tissue kit. Bacterial composition analysis was achieved via a large-scale sequencing,

Identification of the microbes sampled was performed via High-throughput sequencing of V3-V4 hyper variable regions of 16S rDNA on Illumina MiSeq platform. This went on to show that this particular coastline is highly abundant in microbial diversity, with an analysis of  1.3 million quality-filtered sequences.

Results showed the marine gut microbes main species found within Cobia and Pompano were the Vibrio and Photobacterium spp (Gammaproteobacteria). With Pelomonas and Fuscobacterium  (proteobacteria) dominating the milkfish quantity of microbes. All species shared 96 OUT’s while still having their own unique gut microbes. Pompano showed to have the highest number of OTUs with 10,537 unique clusters, milkfish showed to lowest amount with 2799 clusters. Whilst cobia showed to have, 10,435 clusters analysed.

It is believed that these differences are due to the gut morphology of the different species as well as the physiological behaviour and specificity of each fish to be dissimilar. Further research into morphology and physiological behaviour of these species would provide insight.





Original Paper: Comparative profiling of microbial community of three economically important fishes reared in sea cages under tropical offshore environment
M.K. Rasheeda  , Vijaya Raghavan Rangamaran  , Senthilkumar Srinivasan, Sendhil Kumar Ramaiah, Rajaprabhu Gunasekaran, Santhanakumar Jaypal, Dharani Gopal, Kirubagaran Ramalingam