Total Lipid and Cholesterol Content in the Flesh of the Five Important Commercial Fishes from Waters Around Jaffna Peninsula, Sri Lanka
The present investigation was carried out to understand the total lipid and cholesterol content of flesh of five commercially important adult fishes such as Siganus lineatus, Gerres oblongus, Scoliodon laticaudus, Scomberoides lysan and Hemirhamphus marginatus collected from waters around Jaffna peninsula. People living in Jaffna peninsula consume fish as the main source of nutrition in their diet. However they have no definite knowledge, pertaining to which species can be intake with their food without harming their health condition. Therefore studies on the nutritional value of marine food fish is a prime theme of research for fish consuming people. In the northern province of Sri Lanka, no study on lipid and cholesterol content of fish has been done so far and therefore the present investigation was initiated. Total lipid in the flesh of five different fishes was extracted and the cholesterol content was estimated in the present study. Mean total lipid and cholesterol content of five commercially important fishes ranged from 2.63 to 4.41% and 54.2 to 104.5 mg/100 g, respectively. Values obtained for total lipid and cholesterol content of five different fishes were found to be good indication of nutritional values. Highest total lipid content was found in muscle tissue of Gerres oblongus lowest was in Hemirhamphus marginatus. However, highest cholesterol content was recorded for Scoliodon laticaudus and the lowest for Scomberoides lysan. Analysis of Variance (ANOVA) for total lipid and cholesterol content of five different adult fishes showed that there is significant difference (p<0.05) between fishes.
September 25, 2010; Accepted: November 10, 2010;
Published: February 22, 2011
Lipids are the predominant source of energy for fish. The mechanisms by which
fish allocate energy from lipids for metabolism, development, growth and reproduction
are critical for understanding key life-history strategies and transitions (Leaver
et al., 2008). Lipids are the major source of nutrition in marine
fishes (Sargent, 1976; Sargent et
al., 1989). They are considered an efficient biochemical means of concentrating
large amounts of stored energy at small space. The cells of white fat tissue,
called adipocytes, are responsible for lipid synthesis, release and storage
in the organism (Szkudelski et al., 2009). The
major storage sites of fish are mesenteric fat, muscle and Liver (Sheridan,
The fat content in fish muscle is highly variable. It depends on species, age,
spawning season, fish diet, and muscle type (Gehring et
al., 2009). Qualitative studies on the composition of fish flesh have
been investigated frequently (Love, 1970). The live weight
of majority of fish usually consists roughly of lipid 2-12% (Love,
1980; Weatherley and Gill, 1987). The seasonal storage
and utilization of lipid reserves are important in the metabolic activities
and overall life histories of many animals including fish (Love,
1970; Shulman, 1974). Constancy in tissue or organ
function is reflected in the composition and structure of polar lipids, while
neutral lipids vary widely as a result of a balance between dietary intake,
anabolism and catabolism (Sargent and Henderson, 1986).
There are several classes of lipids, all having similar and specific characteristics
due to the presence of major hydrocarbon portion in their molecule.
Lipids can be used as an assay of physiological condition and may reflect resources
availability, metabolic activity or recent stress (Fraser,
1989). Lipids are important fuel for marine organisms especially for those
living in high latitudes (Clarke, 1983). When maternal
diets are deficient, insufficient transfer of lipids to developing ovaries may
reduce fecundity and the viability of the progeny (Watanabe,
1985; Luquet and Watanabe, 1986; Heming
and Buddington, 1988). The role of lipids in reproduction may be just as
critical, supplying energy for activities such as egg development, nest building,
courtship, or protection of young (Meffe and Snelson, 1993).
Slobodkin (1962) and Calow (1977)
noted that fat deposition may actually detract from reproduction, particularly
when fat deposition and reproduction are concurrent.
Triglycerides are compounds where most of the fat calories are stored. The
reserve fats of fish have a mechanical function, maintaining the elasticity
of the outer covers and creating a soft lining for the internal organs (Stroganov,
1962). The major lipids that have direct role in buoyancy of marine fish
are wax esters, squalene and alkyldiacylglycerols. Triacyglycerols and cholesterol
have an indirect role in buoyancy of marine fish. Many fishes in the ocean have
oil-filled bones (mostly triacylglycerols) (Phleger, 1998).
Phospholipids are the main constituents of biological membranes (Bhouri
et al., 2010) and it provides sheaths surrounding the nerve cells
(Sargent and Whittle, 1981; Farkas
et al., 1988). It plays a central role in the embryonic metabolism.
Fish is a major source of food for human nutrition providing an important amount
of dietary protein and lipid diet in many countries (Bouriga
et al., 2010). Compared with red meat, fish flesh is easily digestible
(Pirestani et al., 2010). Fish and fish oil are
the rich source of omega 3- fatty acids. Fish oils have moved into the center
stage of fatty acids in nutrition, it helps to prevent brain aging and Alzheimers
disease (Whelan, 2008). Cod liver oil taken for vitamins
A and D. Fish oil were used as industrial chemical based on paints and linoleum.
The Jaffna Peninsula is an area in Northern Sri Lanka. Jaffna peninsula is surrounded by sea water but connected to mainland via an isthmus called Elephant pass. Jaffna is situated within ten degrees of latitude to the north of the equator. It is in close proximity to the sub-continent of India and separated from it by the Palk Strait and the Bay of Bengal. In addition to agriculture and livestock, fishery sector is an important industry in Jaffna provides major source of food and income for society. Jaffna district alone contributed 26% of the total fish production and 57% of the total dry fish production of Sri Lanka, in 1983.
The fishes selected in the present study are high consumer demand food fishes found in the Sri Lankan coast having high flesh content and good taste. Among the selected five fishes Siganus lineatus, Gerres oblongus and Hemirhamphus marginatus are relatively cheaper than the other two and therefore people living in coastal regions of Sri Lanka frequently consume these fishes even though they did not have any idea about the nutritional composition of these fishes. Scoliodon laticaudus is a delicious food fish in Sri Lanka the whole part of shark can be utilized as food. Shark meat is used for the production of minced fish products such as fish balls, fish cake, fish sausage, fish ham and fish paste and particularly appreciated in other parts of Asia. Sharks fins are also processed and exported to other Asian Countries by Sri Lankans. Shark liver oil is also an important by product of shark. Scomberoides lysan is also an important food fish in Sri Lanka mostly exported to other parts of the world as dry fish.
People living in coastal region of Sri Lanka provide these fishes to pregnant women and feeding mothers. However they have no definite knowledge, pertaining to which species can be intake with their food without harming their health condition. Therefore studies on the nutritional value of marine food fish is a prime theme of research and the results obtain in the present study will provide a detailed understanding on prevention of lipid oriented diseases for a healthy life for the fish consuming people.
In the northern province of Sri Lanka, no study on lipid and cholesterol content of fish has been done so far. As such the present investigation was carried out to understand the lipid and cholesterol content of five commercially important fishes from waters around Jaffna peninsula.
MATERIALS AND METHODS
Sampling of fishes: The commercially valued fishes namely Siganus lineatus, Gerres oblongus, Scoliodon laticaudus, Scomberoides lysan and Hemirhamphus marginatus were selected for the present study. Samples of five commercially valued adult fishes were collected from Point Pedro, Pasaioor and Delft landing centers (Locations of sampling stations are presented in Fig. 1) from March 2010 to July 2010 and brought to laboratory in an ice box. Total body weight was weighed to the nearest 0.1 g and standard length was measured to the nearest 0.1 mm. The fish samples were dissected and the stage of maturation was determined, macroscopically. Only matured adult fishes from the selected species were considered for the present research. Size range of adult fishes and number of observations are provided in Table 1.
Identification of fishes: Collected fishes were brought to the laboratory
and species identification was confirmed using the FAO species identification
guide (De Bruin et al., 1994).
Total lipid analysis: Total lipids in tissue sample were extracted according
to the method of Bligh and Dyer (1959), that is modified
method of Folch et al. (1957). One hundred gram
muscle tissue was cut from the fresh fish, rinsed with distilled water and dried
to constant weight in a drying oven (60°C, 24 h). Dried samples were minced
in a glass blender, homogenized with chloroform: methanol mixture (2:1 V/V),
mixed in a vortex mix in 2800 rpm and filtered. The extract was shaken and equilibrated
with ¼ of its volume of a saline solution. The extracted lipids were
concentrated by a rotary evaporator (IKA RV 10 basic).
||Sampling sites (A, B and C) of fishes from waters around Jaffna
peninsula (A) Point Pedro (B) Delft (C) Passaiyoor
|| Size range and number of observations of fishes examined
Lipids were stored in sealed vials. Extracted lipids were weighed in vials
using a micro electronic balance (±0.001 mg) in order to calculate the
total lipid content. The same procedure was repeated with 24 replicates of each
fish species and the mean value was computed.
Cholesterol analysis: Cholesterol content of fish was estimated by the
Zlatkis et al. (1953) method. Extracted lipids
were treated with ferric chloride, acetic acid mixture and sulphuric acid and
the colour developed was observed. After 20 min absorbance was read at 560 nm
in a spectrophotometer (LABOMED, UVD-3000) at the department of Zoology, University
of Jaffna. The absorbance readings were plotted in a calibration curve and the
relevant cholesterol concentrations were computed. The same procedure was repeated
with 24 adult fish samples of each fish and the mean value was computed.
Statistical analysis: The total lipid and cholesterol content obtained for five different adult fishes were first analyzed by one way analysis of variance (ANOVA). When a single factor ANOVA rejects the null hypothesis i.e., when the mean of the samples was significantly different, ANOVA was followed by Post hoc comparison of means: Duncans multiple range test (DMRT) using STATISTICA software in the computer. The level of statistical significance was set at p<0.05.
Total lipid and cholesterol content: Total lipid and cholesterol content of five different fish species are presented in Table 2, total lipid and cholesterol content of twenty four adult fish samples of five different fishes were subjected in the computation of mean value in the present study. Mean total lipid content ranged from 2.6300±0.060% (Hemirhamphus marginatus) to 4.4117±0.058% (Gerres oblongus) whereas mean cholesterol content ranged from 54.20±1.005 (Scomberoides lysan) to 104.05±0.900 mg/100 g (Scoliodon laticaudus). Values obtained for total lipid and cholesterol content of five different fishes were found to be good indication of nutritional values. Highest total lipid content was found in muscle tissue of Gerres oblongus lowest was in Hemirhamphus marginatus. However, highest cholesterol content was recorded for Scoliodon laticaudus and the lowest for Scomberoides lysan.
Statistical analysis: Analysis of Variance (ANOVA) for total lipid and
cholesterol content of five different adult fishes showed that there is significant
difference (p<0.05) between treatments. Results of Post hoc-Duncans
test is expressed as superscripts in Table 2. Post hoc-Duncans
Multiple Range Test expressed significant different (p<0.05) between five
different fishes at all instances. Box-Whisker plots showing significant difference
in total lipid content and cholesterol content between five different fishes
are shown in Fig. 2 and 3. Significant differences
in mean, standard error for each mean value and standard deviation for each
mean are clearly expressed in Fig. 2 and 3.
||Mean total lipid and cholesterol content of five fish species
from waters around Jaffna peninsula, Sri Lanka. (Values in the column indicate
mean ± Standard deviation)
|Value in the same column with different superscript letters
(a-e) (f-j) within a same nutritional component are significantly different
||Box-Whisker plot showing significant difference in total lipid
content between five different fishes
||Box-Whisker plot showing significant difference in cholesterol
content between five different fishes
Very few studies were carried out on the selected tropical fish species from
other parts of the world. In a study by Al-Jedah et al.
(1999), total lipid content of congeners of the three species of fishes
studied in the present investigation was presented from the coast of Qatar.
The estimated total lipid content for S. commerson was 7.46% (Al-Jedah
et al., 1999) which is higher than the value estimated for S.
lysan in the present study. Al-Jedah et al. (1999)
estimated lowest total lipid content for G. filamentosus than the value
obtained for G. oblongus in the present study. Total lipid content obtained
for S. canaliculatus from Quatar waters (Al-Jedah et
al., 1999) was 3.18% which tally with the present work i.e. for S.
lineatus in the present study was 3.36%. In another study, Zhao
et al. (2007) reported a total lipid value of 2.79%±0.15 for
adult Siganus guttatus from the South China Sea. The recorded value in
the South China Sea is lower than the present estimate computed for a congener
of the Siganus species. The above differences may have been attributed
due to different environmental conditions and nutritional status of those fishes
in different topographical regions.
Further, Childs and King (1993) classified fish into
three categories according to the content of fat, namely the low-fat category
with 0.6-3.0% fat, the medium fat category with 3.5-7.0% fat and the high fat
category with levels that range from 8.1-15.3% fat. The fish caught from the
Northern waters of Sri Lanka tend to fall into the low and medium fat categories,
although it should be noted the fat contents may vary between individual fish
or groups of fish of the same species caught at different times or under different
Among the important five fish species from waters around Jaffna peninsula,
the richest total lipids were observed in Gerres oblongus and the highest
cholesterol content was observed in Scoliodon laticaudus. Bykov
(1996) reported that the fat content for Scoliodon sp. varied between
18 to 23%. Bakes and Nichols (1995) studied about the
liver oils from the deep-sea sharks Somniosus pacificus, Centroscymnus
plunketi, Centroscymnus crepidater, Etmopterus granulosus,
Deania calcea and Centrophorus scalpratus. They analyzed lipid, fatty
acid and squalene compositions of each shark species and found high squalene
content (50-82% of oil) in all species, except Centroscymnus plunketi
and Somniosus pacificus and suggested that the oil from these deep-sea
sharks collected in southern Australian waters is suitable for industrial uses.
The nutritive value of Scomberoides tol was found to be good and it
had 1.6% of lipid and 0.008% of free fatty acid (Patterson
and Ranjitha, 2009). Total lipid content of Siganus fuscescens showed
seasonal variations and were high in winter and low in summer (Osako
et al., 2006). No previous study was done on Hemirhamphus marginatus
and the present investigation is the first record for this species. The present
study indicated that all five species of fish studied presently are intuitively
good and they could be exploited successfully for food and for preparing various
fish by products.
Authors are grateful to the authorities of National Research Council for the financial assistance (Research grant No. 07-19).
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