International Journal of Aquaculture, 2018, Vol.8, No.15, 112-120
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recorded. The geographical locations, season, diet, stage of maturity, and sizes of fish determine the chemical
composition of fish most of the time (Guner et al., 1998; Tanakol et al., 1999).
Edible fish tissue is reported to contain about 60-84% water, 15-24% protein and 0.1-22% lipids. The proportion
of the constituents are species-specific and the main variations in proximate composition between species occur in
moisture and lipids content (FAO/WHO, 2011; Boran et al., 2011; Kocatepe et al., 2012).
Fresh fish tissue has high moisture content. The high moisture content recorded in the fresh samples is a
disadvantage as it predisposes the fish to microbial spoilage, oxidative degradation of polyunsaturated fatty acids
and consequently decreases in the quality of the fishes. Hence, fresh fish is highly perishable. The moisture
content of all the processed samples ranged from 10.20 to 17.67%. Reducing the moisture content of fresh fish by
drying to 25% water content will stop bacterial growth and reduce autolytic activity (Oparaku, 2010). The low
moisture content recorded after processing indicates that the processed fish have the tendency to be stable
compared to fresh fish. Quantitatively, protein ranked second among the components in muscle tissue of fish. The
protein content vary less widely from one species to another (FAO/WHO, 2011). Protein content of fish is
considered low if it is below 15% (Stancheva et al.
,
2013). There was a strong inverse relationship between the
moisture and the crude protein contents (Stancheva et al.,
2013). The protein content after drying and smoking
was higher than 50% for all samples. This indicates that processed fish are rich source of protein.
On the basis of their fat contents, fish species has be classified into four majorcategories: high fat (more than 8%),
medium fat (4-8%), low fat (2-4%), and lean (less than 2%) (Achman, 1989; Doğan and Ertan, 2017; Martins et
al., 2017). Based on the result obtained in this study, red belly can be classified as lean fat fish, while catfish can
be classified as low to medium fat fish. Fat content of mango tilapia was more variable. There exists an inverse
relationship between the water and lipid content of fish and the summation of both frequently spans a range of 78
to 88% (Stancheva et al.,
2013).
This study confirms that the ash and carbohydrate contents were low in all the fish species from both locations.
Fishes have variable composition of proteins and fat, and the energy content is dependent on this distribution. The
lipid level in fish contribute significantly to the its calorie content.
In general, drying and smoking had significantly influence of on the proximate compositions of all the fish types
used for this study. The relative increase in protein, lipids and ash content due to loss/reduction of moisture were
the most prominent changes after the drying and smoking process. This was expected because of increased dried
weight as a result of loss of moisture.
Table 4, Table 5 and Table 6 present the changes in the heavy metals concentration after a storage period of six
weeks. From the tables, it can be observed that all the heavy metals investigated in this study were present in all
the stored fishes from both locations. The lead, cadmium, nickel and arsenic concentrations in most of the samples
showed significant variations after storage. Significant reductions (
p
<0.05) were observed in most cases, while in
some of the samples, there was no effect at all. The arsenic concentration of the samples was more variable, as
increases and decreases were observed after storage.
The packaging materials used were transparent low density polythene bags. Observed reductions may be due to
the ability of the packaging materials in protecting the processed fishes from environmental pollution as heavy
metals are ubiquitous and are usually found in the environment, also the packaging material used probably did not
release any of the metals into the fish during storage.
The European Community (No 1881/2006) sets maximum permitted level for lead at 0.4 mg/kg. Cadmium is
non-essential and highly toxic. The European Community (No 1881/2006) has set the maximum level permitted
for fish food as 0.05 mg/kg. In most food products, the nickel content is less than 0.5 mg/kg (IARC, 1990). The
FAO/WHO (2004) recommended the maximum levels permitted for arsenic in sea food as 5 mg/kg. All the values
reported in the study are lower than their maximum limits, hence the fishes were safe both before storage and after
storage.
