The determination of microbial quality and presence of pathogens and chemical contaminants in aquacultured rainbow trout (Oncorhynchus mykiss) fillets and whole fish from different aquaculture production systems

Abstract

Qualitative and quantitative levels of human pathogens (Listeria monocytogenes, Clostridium botulinum, Salmonella species, Vibrio cholerae, Yersinia enterocolitica and Y. pseudotuberculosis) and general microbial quality of whole aquacultured rainbow trout (Oncorhynchus mykiss) were in compare differing aquacultural systems and growing seasons. Listeria levels and general microbial quality were determined on fillets from three facilities and compared to whole fish. Secondly, in each facility and season, levels of select minerals and heavy metals in edible tissue were determined. Aerobic plate counts for whole fish and fillets ranged from 3-6 logs. Coliform counts were high in many cases, but fecal coliform, and E. coli were comparatively lower. Both whole fish and fillets showed similar Listeria incidence (25-90%) and respective levels of 1.12-21 and 0.36-4.83 MPN/g. Presumptive C. botulinum incidence was 45-95% with levels of 0.46-2.33 MPN/g. Coliform, fecal coliforms, and E. coli counts and Listeria and C. botulinum incidence and counts were significant in plant/year interaction (p<0.05). A significant increase from whole fish to fillets in mesophilic APC, coliforms, and Listeria counts (p<0.05) was observed. No Salmonella, Vibrio cholerae, or Yersinia were isolated from any sample. Levels of Na, Zn, S, Ca, Mg, Mn, and Fe were generally within normal ranges. The heavy metals- As, Hg, Ni, Co, Cr, Mo, Pb, and Cd when detected, were below 0.5 ppm, with the exception of Cd in one sample (60.49 ppm). The presence of both C. botulinum and Listeria would be of concern to processors, although no heavy metals were at levels to cause concern.