Changes in bacterial flora during short-term storage of aquafeed and feed ingredients

Abstract

Bacteriological changes in two shrimp feeds and protein rich ingredients on short-term storage for 60 days were studied. Feed I was a commercial shrimp 'grower' diet and Feed 11, a cost effective diet for shrimp formulated at CMFRI, Cochin. The protein-rich feed ingredients used were fishmeal, groundnut oil cake and soybean flour. Sealed samples were stored under identical conditions at room temperature and were analyzed for bacterial population at 0, 30 and 60 days. The total plate count of feeds and feed ingredients were well within the reported non-degrading limit. Gram-positive cocci (42.8-73%) were dominant in all the five samples. During storage gram-positive cocci showed slight reduction, while, gram-negative rods showed marginal increase. Five hundred bacterial isolates derived from feed and feed ingredients were used for further characterization and identification. The major genera identified were Micrococcus, Arthrobacter and Bacillus. Besides, enumeration of indicator bacteria such as Vibrio, Faecal streptococci, Escherichia coli and Staphylococcus aureus was also done in the feeds and feed ingredients. Feed I1 was devoid of all the above indicator forms, except Vibrio, while, Feed I had all the above groups in varying numbers. Short-term storage (up to 60 d) did not have much effect on bacterial load in feeds and feed ingredients.