ISOLATION, CHARACTERIZATION, AND ANALYSIS OF MICROBIAL CONTAMINANTS IN COMMERCIAL FISH FEEDS AND THEIR POTENTIAL HEALTH HAZARDS

ABSTRACT

This study investigates the isolation, characterization, and potential health hazards of microbial contaminants present in commercially produced fish feeds. The research aims to isolate and identify microbial associates from different fish feed brands, characterize the microorganisms involved, and determine the physicochemical properties of the fish feeds in relation to microbial contamination. Fish feed samples, including Coppens, Sarb, and Multi brands of various sizes, were randomly collected from the Umuahia market. The samples were subjected to microbiological analyses, where serial dilution techniques were applied, and various culture media were used to isolate the microorganisms.

The study successfully isolated several microbial species, including four fungi: Aspergillus flavus, Aspergillus niger, Penicillium sp., and Fusarium sp., as well as five bacterial species: Escherichia coli, Staphylococcus aureus, Streptococcus sp., and Klebsiella sp. Biochemical tests, including Gram stain, catalase, oxidase, and coagulase tests, were conducted to characterize the bacterial isolates. The findings indicate significant contamination risks posed by microbial species in fish feeds, such as Aspergillus sp., which can produce aflatoxins, posing carcinogenic risks to humans, and E. coli, known for its association with fecal contamination.

The physicochemical analysis revealed moisture content ranging from 10% to 16% and pH levels between 6.0 and 7.2, indicating susceptibility to microbial growth in some samples. The study highlights the potential health hazards to both fish and consumers, emphasizing the need for proper handling and storage conditions to mitigate microbial contamination in fish feeds.

TABLE OF CONTENTS

CHAPTER ONE

1.0     Introduction                                           

1.1     Aims and Objectives of the Study

CHAPTER TWO

2.0     LITERATURE REVIEW

2.1     Aquaculture Development in Africa

2.2     Fish Feed Development

2.2.1 Feed Formation and Processing

2.3     Sources and Composition of Fish Feeds

2.3.1 Protein

2.3.2 Carbohydrate

2.3.3 Vitamins and Minerals

2.3.4 Fats

2.3.5 Pigment

2.3.6 Binding Agents

2.4     Common Fish Feeds and Feedstuffs

2.4.1 Vegetarian Feed

2.4.2 Trash Feed

2.4.3 Pelleted Fish Feed

2.4.4 Legumes

2.4.5 Roots and Tubers

2.4.6 Cereals and Ceral By- Products

2.4.7 Oil Cakes and Oil Meals

2.4.8 Feeds of Animal Origin

2.5 Pathogens Associated With Fish Feed

2.5.1 Bacterial Contaminant of Fish Feed

2.5.1.1 Salmonella

2.5.1.2 Bacillus Cereus

2.5.1.3 Staphylococcus Aureus

2.5.2 Fungal Contaminant of Fish Feed

2.6 Human Illness Associated With Consumption of Infected Fish

2.6.1 Salmonellosis

2.7     Cultivable Fishes in Nigeria

CHAPTER THREE

3.0     MATERIAL AND METHODS

3.1     Sample Collection

3.2     Sterilization of Materials

3.3     Media Preparation

3.4     Sample Preparation

3.5     Characterization and Identification of Pure Isolates

3.5.1 Gram Stain Reaction

3.6     Biochemical Tests

3.6.2 Catalase Test

3.6.3 Coagulase Test

3.6.4 Oxidase Test

3.6.5 Urease Production Test

3.6.6     Methyl Red Test               

3.6.7 Indole Production Test

3.6.8    Voges Proskauer

3.6.9  Motility Test

3.6.10  Citrate Utilization Test.

3.6.11  Sugar Utilization Test

3.7     Mycological Examination of the Samples

3.8     Physicochemical Analysis

3.8.1 Determination of Moisture Content

3.8.2  Determination of Ph

CHAPTER FOUR

4.0 RESULTS

CHAPTER FIVE

5.0     Discussion

5.1     Conclusion

5.2     Recommendation

References

LIST OF TABLES

Table 1:           Mean fungal counts from fish feed samples (cfu/g)

Table 2:           Macroscopic and Microscopic Characteristics of Isolated Fungi

Table 3:           Occurrence of fungal isolates from different brands of fish feed       

Table 4            Mean Bacterial Count of Isolate from fish feed samples ( cfu/g)

Table 5:           Occurrence of Bacterial Isolates From Fish Feed

Table 6:           Physiochemical analysis of different brand of fish samples.

CHAPTER ONE

1.0       INTRODUCTION                               

Fish like other animals have a requirement for essential nutrients in order to grow properly. In the wild, natural feeds are available and as the fish forage for there, they are able to meet their needs. When fish is removed from its natural environment to an artificial one, enough food must be supplied in order to enable them grow. Artificial diet may be either complete or supplemental. Complete diet supply with all the ingredients (protein, carbohydrate, fats, vitamins and minerals) are both important and indispensable in fish farming for the optimal growth and health of the fish (Nwabueze and Nwabueze, 2011). Supplemental diet do not contain a full complement of nutrient needed but are used to help fortify the naturally available diets (Riche and Garling, 2003) reported that fish reared in intensive tank systems requires all nutrient in a complete pelleted diet since natural food is limited and fish cannot forage freely for natural foods. This has the advantage of high quality and consistency of diet. Good nutrition in fish production system is essential to economically produce healthy and high quality fish products for human consumption.   

Fish feeds are constantly in contact with environmental organisms and become readily colonized by various microbial species. According to FAO (1987), environmental factors during storage predispose the fish feeds to microbial spoilage. The presence of bacteria in feeds causes their decomposition and subsequently high disease which may be transferred to man when consumed (Karine, 2010). Fungi contamination of fish fed has been reported to result in aflatoxicosis (Asley,1970). Aflatoxins are chemicals produced by fungi like Aspergillus flavus and Aspergillus parasiticus commonly known as mold (Sotolu et al.,2014). Mold infested fish feeds have been reported to impact negatively on the growth of fish (Sotolu et al.,2014). Aflatoxin in fish have been known to be capable of having carcinogenic effect on human consumers of contaminated fish. The occurrence of these microbial strains in fish feeds have been reported to depend on the storage conditions of the feeds particularly temperature.

The quality of fish feeds and the hygienic levels of technological process employed during feed formulation determine the level of risk of microbial contamination aided by temperature. According to Zmyslowska (2000), storage conditions especially temperature and humidity are important factors affecting microbial quality of fish feeds. Improper storage temperature may prolong survival of the microorganisms in fish feeds by enhancing their multiplication and production of toxic substances which may be injurious to fish and consequently to consumers.

Also microbiological composition of the fish feed has a big influence on the weight gain and fish health condition. Especially if there are harmful microorganisms present in the feed that destroy the health condition of the fish which results in the disorder in the digestive metabolism leading to the decrease of the new born fishes or total death. Microbiological status has a cosmopolitan character also because the fast reproduction of the microorganisms can lead to over reading the upper boundary of tolerance for maintaining the health condition and can cause the decrease of the fish production or death, which is a total disaster for the fish farm. That is why it is very important to examine the microbiological status on the fish farm (Dalmacija, 2003).

Rearing of fish in concrete tanks using artificial diet has become a common practice in Umuahia. Several outlets for sale of artificial fish feeds now exist. There is a need to investigate the microbial flora of fish feeds sold in Umuahia. This is to forestall contamination of fish feed and by implication prevent transmission of harmful toxic effects on human consumers of fish.

1.1       AIMS AND OBJECTIVES OF THE STUDY

1.         To isolate microbial associates of different brands of fish feeds.

2.         To identify and characterize microorganisms associated with fish feed and the possible health hazard to fish and consumers.

3.         To determine the physicochemical properties of these commercially produced fish feed in relation to the microbial associates.

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