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This study aimed to determine the prevalence and antimicrobial resistance of bacteria isolated from retail fish and shrimp in Tanzania. A total of 92 fish and 20 shrimp samples were analyzed. Fish samples consisted of 24 Nile tilapia, 24 Nile perch, and 24 red snapper. The isolates were identified by their morphological characteristics, conventional biochemical tests, and analytical profile index test kits. The antibiotic susceptibility of selected bacteria was determined by the disc diffusion method. Out of the 92 samples analyzed, 96.7% were contaminated with 7 different bacterial species. E. coli was the most prevalent bacteria (39%), followed by Klebsiella spp. (28%) and Salmonella spp. (16%). Other species isolated from this study were Staphylococcus spp. (8%), Citrobacter (4%), Shigella spp. (3%), and Pseudomonas spp. (1%). All samples were analyzed for Campylobacter spp.; however, none of the samples tested were positive for Campylobacter spp. Fish from the open-air market were contaminated by six bacterial species: E. coli (40%), Klebsiella spp. (26%), Salmonella spp. (24%), Shigella spp. (6.7%), Citrobacter spp. (6.5%), and Pseudomonas spp. (2%), while E. coli (37%), Klebsiella spp. (33%), Staphylococcus spp. (23%), and Shigella spp. (2%) were isolated in supermarket samples. According to the International Commission on Microbiological Specifications for Foods criteria, 54 (58.7%) and 38 (41.3%) samples were good and marginally acceptable, respectively. E. coli isolates were resistant to penicillin (PEN), erythromycin (ERY), gentamicin (GEN), azithromycin (AZM), and tetracycline (TET), while Salmonella spp. isolates exhibited resistance to gentamicin (CN), tetracycline (TET), penicillin (PEN), and erythromycin (ERY). These results suggest that the presence of these bacteria might cause a health risk/hazard to human beings and may cause disease to susceptible individuals, especially immune-compromised consumers.

The rapid population growth in developing countries has led to strong pressure on capture fisheries. However, capture fisheries have reached their maximal limits of fish production and are supplemented by farmed fish. The growth in aquaculture has led to high demand for fish feeds, which play a very important role in fish nutrition and health. Use of animal protein in fish feeds is expensive; hence, a majority of farmers from developing countries use local feed ingredients from plant origin as a source of dietary protein. However, these ingredients of plant origin provide the best natural substrates for fungi, which can be easily accompanied by mycotoxin development under suitable conditions. The locally made feed comprises ingredients such as soybeans, cottonseed cake, and wheat and maize bran which are mixed together and ground after which the compounded feed is pelleted and stored. Among the ingredients, maize and oilseeds are more susceptible for mycotoxigenic fungi compared to other ingredients. The outcomes of mycotoxin contamination in fish feeds are not different from other animal species intended for human consumption, and they are directly associated with production losses, particularly decreased weight gain and feed conversion, impaired immune system and reproductive performance, and increased fish mortality. Fish may also carry mycotoxin residues along the food chain, thus compromising human health. Hence, it is important to ensure the control of mycotoxin contamination in fish feeds, especially during the production and storage.