MYCOLOGICAL EXAMINATION OF FISH FEED STUFF WITH SPECIAL REFERENCE TO MYCOTOXIN PRODUCTION

Abstract

Mycotoxin contamination is considered as one of the most economic problems for livestock and feed industries. A total of thirty fish feedstuffs were collected for isolation and identification of fungi from fish farms in Kafr El Sheikh Governorate, Egypt. Five fungal genera were isolated from all examined feedstuffs. The most frequent isolated fungi was Aspergillus spp. (86.66%) followed by Penicillium spp. (23.33%), and Fusariam spp. (10%), Mucor spp. (6.66%) then Rhizopus spp. (3.33%). Aspergillus niger was the most prevailing genus (43.33%) followed by Aspergillus flavus ((30%), and Aspergillus fumigatus (6.66%), Aspergillus versicolor (3.33%) then Aspergillus terrus (3.33%). Aspergillus ochraceus was not found despite the presence of ochratoxin A (OTA) in low concentrations. Some mycotoxins were produced by more than one fungal species. Mycotoxins determination using HPLC revealed that 23.33% (7/30) of examined fish feed samples were positive, while 23 samples (76.66%) were mycotoxins free. In positive samples of mycotoxins, aflatoxins (AF) and OTA represented 23.33%, 10%, respectively. The estimated carcinogenic aflatoxins were AFB1, AFB2, AFG1 with a percentage of 23.33%, 13.34%, 6.67%, respectively, but AFG2 was not found. About 42.86% of the AFs producing fish feeds was higher than the permissible limit of aflatoxins (permissible limit is 20 ppb). The aflatoxigenic ability of the recovered nine A. flavus referred to 6 out of 9 (66.67%) were aflatoxin producers. Polymerase chain reaction (PCR) was carried out using the norsolonic acid reductase (nor), versicolorin A (ver-1) and O-methylsterigmatocystin (omtA) as aflatoxin producing genes of the isolated A. flavus strains. From the AF producing A. flavus, 50% was above the permissible limit. Therefore, the high contamination of fish feedstuffs with fungi, AFB1 andlow OTA in fish farms indicated potential risks to fish liveliness, derived products and the health of fish consumers. Key words: fish feedstuff; fungi; aflatoxins; ochratoxin A