INTRODUCTION:

The amount of fish catch from capture fisheries and aquaculture was about 167 million tons in 2014, 146 million tons of it was devoted for human consumption which amounted to 20.1 kg per capita/ year (FAO, 2016). Fish is characterized by the high quality fish protein quality and quantity of essential amino acids and non-essential and the lack of connective tissue, which increases the digestion process (Islam and Joadder, 2005). Fat fish is considered from the finest animal fat to the high content of beneficial polyunsaturated fatty acids in maintaining human health from heart disease and hardening of the arteries, as well as they contain a good proportion of useful in human nutrition saturated fatty acids (Jahncke et al., 1988; Nettleton and Exler, 1992).

Many local studies that have focused on identifying the nutritional value of native fish in marine waters and freshwater recognize her seasonal changes as well as the content of amino acids and fatty acids (Hama and Kamel, 2012).

This study was aimed to compare the chemical composition of three marine fish species (Acanthopagrus arabicus, Chelon subviridis and Cynoglossus arel) which are widely consumed in the local markets of Basrah city, southern Iraq.

Materials and methods:

This study was conducted for the period from November 2013 to September 2014 on three marine fish species; A. arabicus, C. subviridis and C. arel. Fish were classified depending on Kuronuma and Abe (1986) and Carpenter et al. (1997). Samples were collected seasonally from the Iraqi marine waters north-west of the Arabian Gulf by local fishermen. Immediately after catch, fish has been placed in a container filled with crushed ice and transported to the laboratory.

Chemical Analysis:

1- Moisture: eestimated by the method mentioned in the A.O.A.C (2004). meat samples oven dried at 105°C for 24 hours then checked repeatedly until the weight is stabilized and moisture content was calculated according to the following equation:

a= Sample weight with the vine before drying.

b= Sample weight with the vine after drying.

Protein:

Total nitrogen content was estimated according to Semi-microkjeldahl method described in Pearson(1976). Taking the known limits of weight(0.5) gm, From each sample of fish, and then calculated by multiplying the value of the total protein nitrogen value in by 6.25 as in the following equation:

0.0014= Equivalent weight.

Lipid:

The lipid content was estimation using intermittent type Soxhlet device according to the method described in A.O.A.C (2004). The solvent used was n-Hexane and the extracted lipid proportion was calculated using the following equation:

a= Sample weight with the paper before extraction.

b= Sample weight with the paper after extraction.

Ash:

Fish samples (1.5 gm) were incinerated into Muffle Furnace at 550°C for 12 h according to the method described in A.O.A.C (2004). Ash content was calculated using the following equation:

a= Sample weight with the vine after incineration.

b= The vine Blank weight.

Data were analyzed statistically by using the statistical package of SPSS.

Results and discussion:

The results in table (3) Indicate mean weight and length of the fish species studied during the sampling period, as follows:

Table (1) weight and lengths of the fish studied

Mean total weights (gm)	Mean total lengths (cm)	Fish species
100-170	13-40	A. arabicus
50-120	19-35	C. subviridi
9-53	14-38	C. arel

Table (4) demonstrates the chemical composition of fish during the study period. The statistical analysis revealed no significant differences (P>0.05) in moisture contents between fish species. Highest moisture was recorded in C. arel during the summer (79.14%) while A. arabicus recorded the lowest moisture content amounted to 72.11% during autumn. This range is comparable to the moisture content in fish Tenualosa ilisha and Chirocentrus dorab (74.39% and 60.48% respectively) (Al Bayati, 1997; Al-Abdul-Nebi, 2003).

Table (2). The chemical composition of fish A. arabicus.

Season	Moisture	Ash	Protein	Fat
Winter	73.87	3.49	19.25	3.22
Spring	70.8	4.16	20.12	4.23
Summer	75.32	3.11	19.24	2.14
Autumn	72.11	5.15	19.44	3.13

Table (3). The chemical composition of fish C. subviridis.

Season	Moisture	Ash	Protein	Fat
Winter	76.35	1.87	17.14	3.64
Spring	74.82	2.18	17.97	3.88
Summer	78.66	1.55	16.6	2.17
Autumn	75.7	1.79	18	2.64

Table (3). The chemical composition of fish C. arel.

Season	Moisture	Ash	Protein	Fat
Winter	76.22	6.34	15.17	1.48
Spring	75.2	7.18	15.79	1.79
Summer	79.14	4.73	14.18	1.4
Autumn	76	8.1	14.27	1.5

As for protein contents, no significant differences were observed (P>0.05) between examined fish. Fish A. arabicus recorded the highest percentage of protein (20.12%) during spring, while the lowest recorded protein percentage was 14.18% recorded in the C. arel. These results are comparable to protein content of Ilisha megalopteran 16.01% mentioned by Jasim and Al-Shatty (2002).

The nature of food have an effect on protein content in fish. Carnivorous fish gain more protein through diet thus have higher protein content. As indicated from the results in a table (2), no significant differences (P>0.05) were detected in lipid content between the studied species. Fish species A. arabicus showed the highest percentage of lipids (4.23 %) during the spring compared with lower lipid content recorded in the species C. arel (1.4%) during the summer. These results are compatible with the results in the study of Jasim and Al-Shatty (2002) where they recorded lipid content in Ilisha megaloptera within the range of 3.5- 4.52%. This may be due to the nature of feeding of the species and the abundance of food. Some species also showed existence of the inverse relationship between lipid and moisture (Jonsson, 2007). The increase in the lipid content in fish is often accompanied by a decrease in the percentage of moisture and vice versa. This variation may exist because of the different species and the season as well as the migration of some fish and consuming lipids as an energy source for migration purposes and reproduction leaving high moisture contents.

Statistical analysis shows significant differences (P<0.05) in ash contents between the studied fish species. Highest content was recorded in C. arel (7.18%) during spring while the lowest percentage was recorded in C. subviridis (1.55%) during summer. These results are higher than those detected in L. megaloptera as studied by Hnadi et al. (2001) and Jasim and Al-Shatty (2002) which amounted to 3.27% and 1.19%, respectively. The marine environment where fish are live could affect the ash content compared to freshwater due to the higher content of mineral elements as suggested by Al- Shatty (2006).

The statistical analysis of moisture content in the fish A. arabicus showed no significant differences (P>0.05) between seasons except for spring with the summer where significant differences (P <0.05) were detected. There are also significant differences in lipid, ash and protein contents during the seasons of the year. The study of Al-Mudhafr (2009) which indicated that fresh fish A. arabicus contained 71.43 % moisture, 4.1% fat and 20.35 % protein is comparable to the results of the current study, except for ash which amounted to 1.4% and was lower than the percentage of ash.

In C. subviridis, the statistical analysis showed no significant differences (P>0.05) in moisture content except for the spring with the autumn, where differences are significant (P <0.05). The ash, protein and lipid contents showed no significant differences (P> 0.05) between seasons as indicated by statistical analysis. Al Bayati and Abdul Rahim (2009) studied the chemical composition of mullet fish which contained 18.7% protein, 1.5 % Ash, 76.6% moisture and 2.9% lipid. Their results were comparable to the results of the current study during year seasons. From the statistical analysis, it was indicated that the species C. arel showed no significant differences (P> 0.05) in moisture and protein contents, while lipid content showed significant differences (P> 0.05) between seasons except for winter with both summer and autumn and for summer with autumn.

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Received on 01.01.2017 Modified on 24.02.2017

Research J. Science and Tech. 2017; 9(2): 231-233.

DOI: 10.5958/2349-2988.2017.00041.9