Tracing contamination to its ultimate source is considered difficult as multiple factors affect
stable microbial community in culture water. Feed, covering over 60 percent of production
cost although less considered, could represent a significant source of fish diseases, the major
constraint in aquaculture production. The present study based on the sensitivity of quantitative
Polymerase Chain Reaction (qPCR), and sequencing analysis was undertaken to determine the
microbial load in fish feed and its potential to cause disease outbreaks in aquaculture farms in
Ghana. From the general screening of a total of 30 feed samples, 90% were positive for
bacterial contamination, 70% for fungal contaminations, with 40 % showing multiple
contaminations with both bacterial and fungal pathogens Three important bacteria pathogens
(Streptococcus iniae, Streptococcus agalactiae and Staphylococcus aureus) implicated as
major causes of fish diseases occurred at prevalence rates of 89 %, 60 % and 60 % respectively
in the fish feed and with average concentrations(Ct values) of 28.39, 40.78 and 34.26.
Additionally, sequencing analysis based on the 16S rDNA gene of bacteria and at less than
96% identity, revealed the presence of three different genus of bacteria, and six different
species, representing a profile of over 50 different strains of bacteria from the Sphingomonas
genus. A positive correlation (0.667) existed between the prevalence rate of bacteria species
in fish feed and that in diseased fish (P<0.05). Also, the prevalence rate of bacteria isolated
from the gut of fish (26.09%) were significantly (P<0.05) similar to that from diseased portions
(26.89%). Although mode of transmission of most infections are known to be largely through
the water in which the fish are submerged, prevalence rate of S. iniae (32 %) and S. agalactiea
(24%) were significantly(p<0.05) lower in water samples than that in the feed (89%, 60%)
respectivelyIn addition, Staphylococcus aureus which was not isolated from the culture water
samples at all, occurred at a prevalence rate as high as 60 % in fish-feed. This thus confirms
contamination of fish-feed as a significant pathway for entry of pathogens. Evaluation of
microbial quality of fish feed as a routine practice on farms should therefore be enforced |
University of Cape Coast