Introduction

Fish is a staple article food in the tropics. It is a cold- blooded vertebrate, living wholly in water and breathing through gills, with fins for swimming. It is a good source of protein, has vitamins such as Vitamins A and D and also minerals like calcium and phosphorous. Fish is of high biological value, it has essential sulphur containing amino-acids such as lysine and methionine4. The flesh from healthy fish contains 60-84% water, 15-24% protein, 0.1-22% fat and 1-2% minerals7.

Fish pellet is from a generic term for a nutrient rich feed ingredient used primarily in diets for domestic animals, sometimes used as a high quality organic fertilizer. Fish pellet can be made from almost any type of seafood but is generally manufactured form wild caught, small marine fish that contains a high percentage of bones and oil, and usually deemed not suitable for direct human consumption. These fishes are considered ‘industrial’ since most of them are caught for sole purpose of fishmeal and fish oil production. A small percentage of fish pellet is rendered from the by-catch of other fisheries, and by-products or trimmings created during processing of various seafood products destined for direct human consumption15.

The high quality and concentration of essential nutrient, especially of well balanced amino acid, essential fatty acids and energy content makes fish pellet an indispensable ingredient in diet of most aquaculture species and many land-farm animals. Because of these nutrient content, high digestibility and palatability, fish pellet serves as the benchmark ingredient in aquaculture diets15.

The quality of different feedstuff is generally dependent on the amino acid profile in their proteins, digestibility of proteins, freshness of raw materials, and their storage. Plant based proteins, even when properly processed, are usually not as digestable as fish pellet; and their inclusion rate into the diet is often limited as it results in depressed growth rates and feed intakes. Over-all protein digestibility value for fish pellets are consistently above 95%. In comparison protein digestibility for many plant based proteins varies greatly, for example, from 77% to 96%, depending on the species of plant used for feed preperation14. The quality of fish pellet and the effectiveness of fish pellet production process are important issues for both fish pellet suppliers and fish farmers. This would in turn result in an overall positive economical effect in the fish pellet production14.

A very important reason why fish pellet is sought after as an ingredient in aquaculture diets is because fish pellet contains certain compounds that make the feed more acceptable and agreeable to taste (palatable). This property allows for the feed to be ingested rapidly, and will reduce nutrient leaching14.

Thus, this study was therefore undertaken to investigate the microbiological safety of the available fish pellet sold in Oyo market.

Material and Methods

Collection of Samples:

Six bags of the pellet in duplicates were purchased from retailers in Akesan market within Oyo metropolis, Nigeria. They were named as A, B, C, D, E, and F. These samples were immediately taken to the laboratory for analysis.

Physico-chemical parameters

Determination of pH and Moisture content.

The pH was determined with a pH meter Pye model 292 MK 3 Unicon. The moisture content was determined using the method described by AOAC3. The pH of the sample was measured by dissolving l.0g of the sample in 10ml of distilled water, the electrode inserted in the solution and reading taken.

Microbial assay

Viable counts of bacteria in the samples were determined with standard plate count agar employing suitable tenfold serial dilution of the samples in 0.1% peptone water as described by APHA1 using the pour plate method. While the coliform count was determined using MacConkey agar and maintained at 370Cfor 48hrs. Fungal load was assessed on potato dextrose agar (PDA) incubated at 27±10c for 72hrs10.

Representative colonies of bacterial isolated were selected and purified by subculturing on nutrient agar using the streaking method. Pure cultures were then characterized and subsequently identified according to Cowan and Steel’s Manual for the identification of Medical Bacteria6. While fungi were identified according to Kulwant12.

Results and Discussion

The mean pH (Hydrogen ion concentration) and Titratable acidity (TTA) of the samples are shown in Figure 1. The pH ranged between the 5.0 and 5.80; while TTA ranged between 4.95 and 0.08. The pH values obtained shows that the pellets are slightly acidic, thereby indicating that pellets could permit and tolerate the growth of bacteria and fungi11 (Figure 1). The ability of fungi and bacteria to survive pH alone is not sufficient parameter to predict the chances of survival and proliferation of bacterial in pellets13.

Fig. 1: pH and tiratable acidity of fish pellets.

Figure 2 shows the percentage moisture content of the pellet sample which ranged between 5.00% and 10.00%. The moisture content obtained is generally low. High moisture content has been reported to accelerate food spoilage17; if low moisture content is held under humid condition it is able to support growth of moulds. If the water absorption continues to rise bacteria will be able to grow.

Fig. 2: Percentage moisture content of fish pellets.

The total bacterial, coliform and fungal count of the examined samples is shown in Table 1.The bacterial counts ranged from 0.0 to 17.0 x 104 cfu/g, coliform count ranged from 0.0 to 74 x 104 cfu/g while the fungal count ranged from 0.0 to 2.0 x 104 cfu/g. It is observed that Sample F has the highest number of bacteria value while Samples C has no bacteria growth while. Sample E has the highest number of coliform value 74 x104 cfu/g .whereas samples A and B has no coliform. Table 2 shows the distribution and occurrence of bacterial and fungal species isolated among the pellet sample. The high bacteria, coliform and fungi counts obtained may be due to poor hygienic standard of preparation, or handling and storage (Table 1)2. Some of the organisms isolated have been implicated as causative agents of gastroenteritis16.

Table 1: Total fungal, bacterial and coliform counts in pellet samples.

Table 2: Distribution of bacterial and fungal isolates among samples.

Key : + = Present, – = Absen.

A total of six bacterial species were isolated from the samples and they were identified to be Streptococus sp, Bacillus sp, Stapylococcus epidermidis, Klebsiella sp, Salmonella sp, and Staphylococcus aureus. It can also be seen that Stapylococcus aureus is the major bacterial contaminants. Sample E has the highest number of contaminant while Samples A and D has lowest bacterial contaminant in them.

The presence of Staphylococcus aureus and other related species like Staphylococcus epidermis indicates contamination by human19. Staphylococcus aureus is carried in the nose of 50% of healthy people5. Its’ occurrences in the fish feed may be through activities such as sneezing and coughing of the feed handlers. The organism is associated with enterotoxin characterized by short incubation period, violent nausea, vomiting and diarrhea. The occurrence of Bacillus sp is an indicative of environmental contamination from soil or dust and has been considered to be one of the important spoilage organisms.

Epidemiological evidence has implicated food as a vector of pathogenic organisms89. When these organisms affect fishes and ingested, this would cause greater harm to human health. Salmonella sp are responsible for causing salmonellosis characterized by typhoid, paratyphoid fever and dysentery18. Klebsiella sp causes gastro-intestinal tract infection.

The fungal species were Aspergillus niger, Rhizopus stolonifer and Mucor sp. None of the samples contain all the organisms. The presence of Aspergillus in the sample could be because Aspergillus is a common soil fungus5. This can get into the feed sample in the process of milling when the producer is so careless to have put some of the feed quantity which has poured on the floor into the bag containing the feed grounded from the machine, this process could introduce the organism into the feed. Also it might have gotten into the grains during dehusking and shelling of grains on the farm and consequent packing from the floor as practiced by many local farmers. Saprophytic soil and air microflora such as species of Mucor and Rhizopus predominate. The presence of this organism can affect the good health of fish and the consumers.

Since it is neither possible nor desirable that we should live in a sterile environment, what is important is to minimize the contamination of feed materials. High hygienic production and appropriate storage conditions should be ensured.