Diversity of Moulds, Sources of Contamination, Moisture Content and Aflatoxin Levels in Fish and Fish Feeds in Kisii County, Kenya
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Date
2024-02
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Kenyatta University
Abstract
Aflatoxins are toxic substances produced by some members of Aspergillus species
which commonly invade foodstuffs as well as animal feeds. When consumed in
quantities exceeding 10 µg/kg, they cause nephrotoxic and hepatotoxic effects in
humans and other animals. Data on the levels of aflatoxins in fish and fish feeds sold
in Kisii County is not available. This study was carried out to assess the diversity of
moulds associated with fresh, sundried fish and fish feeds sold in selected markets in
Kisii County, determine aflatoxin levels in sundried fish and fish feeds, evaluate the
relationship between aflatoxin levels and moisture content in sundried fish and fish
feeds and assess sources of fungal contamination of sundried and fresh fish sold in
selected markets in Kisii County. Samples of sundried and fresh fish from retailers in
four main markets in Kisii County were obtained by random sampling. Samples from
fish farmers in Kisii County and shores of Lake Victoria were obtained to serve as
control. Commercial and home-made fish feeds were purposively obtained from five
main outlets and three self-help groups respectively. Moisture content of all samples
was determined by oven drying and the levels of aflatoxin in sundried fish and fish
feeds determined by ELISA. Isolated moulds were identified using macroscopic and
microscopic characteristics and Sanger sequencing technique. Sources of fish
contamination were determined using a structured questionnaire and level of
contamination expressed as cfu/g. Data on aflatoxin levels and colony forming units
in different types of fish and fish feed samples was analysed using one-way analysis
of variance. The means that were significantly different were separated using
Tukey’s HSD test. Two-way analysis of variance was used to analyse the interactions
between markets and type of fungi, types of fish feeds and fungal species, markets
and types of fish. Data from molecular work was analysed using MEGA version 4.
Relationship between moisture content and aflatoxin levels in fish and fish feed
samples was analysed using regression analysis. Thirty fungal species from fourteen
genera namely; Acremonium, Alternaria, Aspergillus, Candida, Cladophialophora,
Cladosporium, Cunninghamella, Fusarium, Microporum, Mucor, Penicillium,
Phoma, Trichoderma and Verticillium species were isolated from fresh and sundried
fish samples. Eighteen fungal species were isolated from commercial and home made fish feeds. They comprised of eleven genera; Alternaria, Aspergillus,
Aureobasidium, Cladosporium, Eurotium, Fusarium, Mucor, Penicillium,
Stachybotrys, Trichoderma and Rhizopus species. Aflatoxin levels in sundried fish
ranged from 20-840 ng/kg and 80-500 ng/kg in fish feeds. The cfus/g from control
samples were significantly low compared to those from fresh and dried fish samples
(p < 0.05). Transportation, handling and storage were found to be sources of fish
contamination. The relationship between moisture content and fish, moisture content
and fish feed was statistically significant (R2 = 0.942, p = 0.000) and (R2 = 0.797, p =
0.000) respectively. The findings of this study offer new insights into the levels of
aflatoxins and associated fungi in fish and fish feeds sold in Kisii County. Therefore,
there is need for frequent surveillance on aflatoxin levels in dried fish and fish feeds
sold in this County.
Description
A Thesis Submitted in Fulfillment of the Requirements for the Award of the Degree of Doctor of Philosophy (Microbiology) in the School of Pure and Applied Sciences of Kenyatta University, February 2024.
Supervisors
1. Ethel Monda
2. Omwoyo Ombori
3. Johnson Kwach