Mycobiota and aflatoxin B۱ contamination of rainbow trout (Oncorhinchus mykiss) feed with emphasis to Aspergillus section Flavi

  In the present study, mycobiota and natural occurrence of aflatoxin B۱ (AFB۱) in pellet feed and feed ingredients used in a feed manufacturing plant for rainbow trout nutrition was investigated. The samples were cultured on the standard isolation media for ۲ weeks at ۲۸ ºC. Identification of fungal isolates was implemented based on the macro- and microscopic morphological criteria. AFB۱ was detected using high performance liquid chromatography (HPLC). Based on the results obtained, a total of ۱۰۹ fungal isolates were identified of which Aspergillus was the prominent genus (۵۷.۰%), followed by Penicillium (۱۲.۸۴%), Absidia (۱۱.۰۱%) and Pseudallscheria (۱۰.۱۰%). The most frequent Aspergillus species was A. flavus (۶۰.۶۶%) isolated from all feed ingredients as well as pellet feed. Among ۳۷ A. flavus isolates, ۱۹ (۵۱.۳۵%) were able to produce AFB۱ on YES broth in the range of ۱۰.۲ to ۶۱۲.۸ µg/g fungal dry weight. HPLC analysis of trout feed showed that pellet feed and all feed ingredients tested except gluten were contaminated with different levels of AFB۱ in the range of ۱.۸۳ to ۶۷.۳۵ µg/kg. Unacceptable levels of AFB۱ were reported for feed including soybean, fish meal and wheat. These results indicate the importance of AF contamination of trout feed in amounts higher than the acceptable level as a risk factor for fish farming production.