Title: Microbiology and Spoilage Trail in Nile Perch (Lates niloticus) on Lake Victoria, Tanzania

The microbiological spoilage trail and storage time for iced whole Nile perch (Lates niiloticus) and chilled fillets were studied. Similarly, microorganisms of surface lake water, bottom sediments and whole Nile perch from fishing grounds in Mwanza gulf was analyzed in phase I. Phase II and III included iced whole Nile perch, laboratory and four establishments' chilled fillets, and all were stored at 0-3°C during shelf life study. Hence, the main goal of the study was to check prevalence of certain human pathogens, main spoilage organisms and establish shelf life (storage time) as well as effect of short and long storage of whole Nile perch in ice prior to processing into chilled fillets.

The results showed variable bacteria counts for sediments and Nile perch guts while lake water results were approximately below method detection limit 0-20cfu/ml. It was concluded that human pathogens occasionally may be derived from fishing grounds environments. The average keeping quality (shelf life) in days for iced whole Nile perch, laboratory and establishments chilled fillets were 26-28æ 17æ 8-13 days respectively. Shelf life was short (8 days) for Nile perch fillets produced from long time (17 days) stored whole Nile perch in ice before processing. In this work, the main spoilage organism's composition in spoiled whole Nile perch and chilled fillets may include Shawenella putrefaciens, Vibrionaceae / Aeromonas, Pseudomonas, and Enterobacteriaceae. For both sensory/organoleptic (QIM score) assessment and microbiological methods were consistent while chemical method was not reliable during early storages. Accordingly it was suggested that the chemical (TVB-N) parameter is not reliable indicator for freshness quality of iced whole Nile perch as well as chilled fillets.