en aquaculture aquaculture پژوهشي Orginal research papers <p>  In the present study, mycobiota and natural occurrence of aflatoxin B₁ (AFB₁) 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 2 weeks at 28 ºC. Identification of fungal isolates was implemented based on the macro- and microscopic morphological criteria. AFB₁ was detected using high performance liquid chromatography (HPLC). Based on the results obtained, a total of 109 fungal isolates were identified of which <i>Aspergillus</i> was the prominent genus (57.0%), followed by <i>Penicillium</i> (12.84%), <i>Absidia</i> (11.01%) and <i>Pseudallscheria</i> (10.10%). The most frequent <i>Aspergillus</i> species was <i>A. flavus</i> (60.66%) isolated from all feed ingredients as well as pellet feed. Among 37 <i>A. flavus</i> isolates, 19 (51.35%) were able to produce AFB₁ on YES broth in the range of 10.2 to 612.8 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 AFB₁ in the range of 1.83 to 67.35 µg/kg. Unacceptable levels of AFB₁ 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. </p> Aflatoxin, Oncorhinchus mykiss, Aspergillus flavus, Mycobiota, Troutfeed 363 374 http://jifro.ir/browse.php?a_code=A-10-1-102&slc_lang=en&sid=1 S. Alinezhad 10031947532846001589 10031947532846001589 No M. Tolouee 10031947532846001590 10031947532846001590 No A. Kamalzadeh 10031947532846001591 10031947532846001591 No A. A. Motalebi 10031947532846001592 10031947532846001592 No M. Nazeri 10031947532846001593 10031947532846001593 No M. Yasemi 10031947532846001594 10031947532846001594 No M. Shams-Ghahfarokhi 10031947532846001595 10031947532846001595 No R. Tolouei 10031947532846001596 10031947532846001596 No M. Razzaghi-Abyaneh mrab442@yahoo.com 10031947532846001597 10031947532846001597 Yes