The status of Channa punctatus (Bloch 1793), the snake headed murrel
in relation to human health

SUBROTO GHOSH, Ph.D

Department of Zoology

Fisheries and Aquaculture Unit (Post Graduate section)

Rishi Bankim Chandra College

Naihati 743165

West Bengal, India

Submitted to and Published by Biology Online.

 

Fish is the more common source of
nutrition in the diet of the common Indian. As Ackman (2000) puts it "it is
indisputable that fish is in all respects a healthy food" and in the backdrop
of a need to understand the nutritional values of the fish items in the diet of
the common man in India, it is thought essential to investigate the composition
and distribution of lipids and fatty acids in a very common Indian fish vis-à-vis
its role as a nutritional component in regard to the atherogenic and
thrombogenic indices.

Interestingly enough one
finds that most of the lipid studies are based on fish oil.  Dyerberg et al. (1975, 1978) had
reported a low rate of coronary mortality amongst the Greenland Eskimos whose
diet included a strikingly higher intake of n-3 PUFA from their marine food
sources like seals and whales. The Zutphen Study of Keli et al. (1994)
was based on fish consumption and the risk of stroke. The Lugalawa study in Tanzania
carried out by Pauletto et al. (1996a, b) showed similar results with
fish in the diet. Silva et al. (1996) stated that fish consumption is an
important modulator of fish oil efficacy and concluded that the triacylglycerol
(TAG) lowering effect of fish oil is affected by fish consumption. Yamada et al. (2000) declare that diets
rich in fish are associated with a decrease in the incidence of atherosclerosis
and that is related to the n-3 fatty acid content of the fish. Bays et
al. (2003) state that marine fish oils rich in n-3 fatty acids lower TAG
and may be effective in combination with statins to treat combined hyperlipidaemia.
Upadhya et al. (2002) state that high cholesterol diet increases lipid
peroxidation in erythrocytes, spleen and aorta. But according to them dietary
fish oil is protective against peroxidative damage caused by the high
cholesterol diet. They believe that this could be due to the fact that PUFA in
fish oil increase the utilization and uptake of cholesterol.

Channa punctatus
(Bloch 1793) is a freshwater common green snake-headed spotted murrel belonging to the
family Channidae of the order Channiformes and has accessory respiratory organs
that help the fish to survive in inhospitable situations. It has a natural
distribution in India
and the other neighbouring countries. C. punctatus in having a low
content of fat and found abundantly enough have strangely not found the
attention of nutritionists.    

Channa punctatus can very well be termed
as a ‘lean’ fish because of its very low lipid contents through out the year. Moreover
these fishes have very little or no adipose tissues. According to Ghosh (2006)
the Total Lipid (TL) of body flesh of C. punctatus is very low and is
highest during the pre-breeding season, which is ca. 0.5%. The TL
content in the pre-breeding and in the post-breeding seasons are pretty less in
the body flesh of C. punctatus. The average TL content through
out the year comes to about 0.37%. This may be an important reason for
the easy digestibility of this species, according to Ghosh (2006).

Ghosh
(2006) reports that in C. punctatus, TL decreases as the fish moves from pre-breeding to breeding
and further on to the post-breeding season. The TL of liver is high. The
breeding season profile is an indication that the fish utilizes lipid for
oogenesis and this is reflected in the total lipid profiles of the roes. The TL
of the roe of C. punctatus is
exceptionally high.

According to Ghosh (2006)
of the three fractions i.e. Phospholipids
(PL), Neutral Lipids (NL) and Glycolipids (GL) PL are the major one in the
flesh and are found maximally in the post-breeding season. The NL content
remained more or less around 40 % w/w of TL through out the year. The GL remain
the minor fraction. The Hydrocarbons-Wax esters-Steryl esters (HC-WE-SE)
combine in the flesh is notably low in the pre-breeding season and noticeably
high in the breeding. HC are the major component while WE and SE are nominally
present. Triacylglycerols (TAG) in the flesh of C. punctatus are
markedly high in the pre-breeding and very low in the breeding season. Free Sterols
(ST) as % of TL are below 1 in the breeding season and as % of NL they are a
little above 1. Amongst the PL components Phosphatidylethanolamine (PE) is the
major fraction in the pre-breeding, Phosphatidylinositol (PI) in the breeding
and Phosphatidylcholine (PC) in the post-breeding season. Sphingomyelin (SM) is
found in a moderate amount in the breeding and pre-breeding but low in the
post-breeding season.

It has been seen that
those fishes which have very low lipid content in their flesh always have high
lipid contents of all classes in their livers. According to Ackman et al. (2002)
this suggests that the liver is the chief site of lipid synthesis and storage. The
lipid content in the liver of C. punctatus is high (Ghosh, 2006).

The ST % falls
appreciably in the breeding season and again rises in the post-breeding season
but through out the year it is important to note that C. punctatus
has a low % of ST. The ST as % w/w of TL in the body flesh and liver in the
breeding season show a low profile, according to Ghosh (2006). He had also seen
that ST in the flesh increase many
folds in the post-breeding season.

The
C. punctatus liver has the TAG as the major
component while in all other tissues of it is the HC-WE-SE combine (Ghosh,
2006). HC are the main part of this combine. SE are low in the flesh through
out the year but in the liver they are quite high unlike that in the breeding
season. This high level of SE in the post-breeding liver is a vital indication
of the accentuated activity of the liver in the fatty acid synthesis for the
spawning phase of the life cycles. WE
are an important constituent of simple lipids and are a major component of
depot fats (Christie, 1982) and their low % in the flesh of C. punctatus irrespective of its reproductive cycle
phase indicates the lean quality of the fish meat.

The TAG of the body flesh
and liver of C. punctatus are much higher in the pre-breeding
season. It is lowest in the breeding season. As the fish prepares for breeding
the TAG contents of the liver increase.according to Ghosh (2006). The TAG are
more often storage lipids and reflect the fatty acid composition of the diet to
a greater extent than do the phospholipids. According to Ackman et al.
(2002) the occurrence of a higher amount of TAG in the flesh suggests a need
for a reserve to meet a higher physical and metabolic activity in the animal. The
TAG of the flesh of C. punctatus is 10.23% (Ghosh, 2006). 

In C. punctatus the liver of the breeding season has no
detectable amount of cholesterol. This is very significant. In humans
the liver together with the intestine account for about 10 % each of total
synthesis (Mayes and Botham, 2003). In the fish, too, liver is a site of
synthesis. C. punctatus adult being fundamentally a carnivore
(Chondar, 1999) feeds on aquatic insects, shrimps, gastropods and fishes; and
their feeding activity is highest in the pre-breeding season. Naturally, in the
breeding season there is no detectable amount of cholesterol in the liver as
dietary cholesterol inhibits hepatic synthesis (Mayes and Botham, 2003). The
post-breeding season flesh of C. punctatus has high
cholesterol.  22-Dehydro-cholesterol has
been detected by Ghosh (2006) in the breeding and the post-breeding seasons. 22-Dehydro-cholesterol
is an intermediate step in the synthesis of cholesterol and its presence in the
liver once again proves that the liver is a site for its synthesis.

The principal fatty acids
out of the 35 detected in the fish of C. punctatus does correspond
with Ackman’s list of 14 fatty acids that are "really needed to describe the
fatty acids of fish" (Ackman, 2000). Major fatty acids found in C. punctatus
are myristic (14:0), palmitic (16:0), stearic (18:0), oleic (18:1n-9), linoleic
(18:2n-6), a-linolenic (18:3n-3),
arachidonic (20:4n-6), eicosapentanoic
acid (EPA) or timnodonic (20:5n-3) and decosahexanoic
acid (DHA) or cervonic (22:6n-3). g-linolenic (18:3n-6) is
present as a minor component. It is interesting to note that an important fatty
acid like palmitoleic (16:1n-7) is absent in the fish as are lauric acid
(12:0), myristoleic acid (14:1n-9) and hexatrienoic acid (16:3n-4) whereas pentacosanoic acid (25:0) is
present only in breeding and post-breeding liver. DHA (22:6n-3) is not
detected in the breeding C. punctatus flesh. Another important feature in
this fish is the absence of an eicosatrienoic acid (20:3n-9). This indicates
that there is no fatty acid deficiency in the fish (Ackman, 1994a).

Stearic acid, a saturated
C₁₈ fatty acid increases in both the tissues of C. punctatus
as the fish prepares for spawning. Moreover, they have the essential fatty
acids (EFAs) like linoleic (18:2n-6), arachidonic (20:4n-6) and linolenic
(18:3n-3) which they get from plant sources via
their food chain as fishes like all other animals lack the D12- and D15-desaturases and so cannot synthesise the EFAs. Linoleic can convert
into linolenic and then further into arachidonic by desaturation and by chain
elongation. Both these fatty acids are present in the fish in the right balance
as worked out by Okuyama (2000). Arachidonic acid, which is the main product of
the elongation and desaturation of linoleic acid, also has EFA activity. It is
one of the principal precursors of prostaglandins (Christie, 1982). The
presence of the minor component g-linolenic (18:3n-6) is
important, as it is a precursor of a family of PUFA. EPA and DHA are both
present in considerable amounts making the fish a good source of n-3 PUFAs.

C₁₆ and C₁₈
are more than C₂₀ and C₂₂ acids. Freshwater fish can
convert C₂₀ PUFA to a number of eicosanoids with the help of
cycloxygenase and lipoxygenase enzymes (Henderson,
1996). Octadecatetraenoic acid in TL is of non-detectable amount (i.e.<0.001) except in the pre-breeding
season when it is in a low amount. But DHA occurs in good amount. This
indicates that C. punctatus efficiently converts the C₂₀ PUFAinto EPA and to DHA.

The fat quality was
evaluated by the atherogenic index (AI) and the thrombogenic index (TI) according
to Ulbricht and Southgate
(1991). It is evident that both the AI and the TI indices for C. punctatus
are present in fair amount through out the year. AI varies from 0.95 to 0.56 in
the flesh TL and TI varies from 0.37 to 0.41. The TI for the fish flesh
suggests a high anti-thrombogenic quality of this fish meat. This is in stark
contrast to the TI values of beef (1), lamb meat (1.4) and milk-based products
(2.1) (Amerio et al., 1996).

C. punctatus
being part of the diet have a definite benefit on human health. The long chain
n-3, popularly called omega-3 (w-3), fatty acids like EPA
(20:5n-3) and DHA (22:6n-3) have been proved beyond doubt of their beneficial
roles (Burr et al., 1989; von Schacky, 1992; Bigger and El-Sherif, 2001;
Christensen et al., 2001). EPA has a protective effect against
thrombosis, atherosclerosis and other inflammatory diseases while DHA is
effective in skin disorders, aids in the development of brain and a part of the
retina. (Lee et.al., 1985). EPA also reduces the concentration of
cholesterol and triacylglycerol in the plasma by lowering the rate of synthesis
of LDL and VLDL by the liver and vascular tissues (Illingworth et.al.,
1984). The n-3 fatty acids have been shown to modify several key risk factors
for cardiovascular disease. The benefits include increased HDL₂-cholesterol
concentrations, reduced TAG-rich lipoprotein concentrations and others (Nestel,
2000). Pownall et al. (1994) had found that an addition of fatty acids
to the diet lowers TAG levels particularly in patients with
hypertriglyceridemia. This effect is not seen with plant sources of n-3 PUFA
(Kestin et al., 1990).

Connor (1994) had listed five
putative mechanisms of diatary n-3 PUFA on lipoprotein metabolism in humans The
reduced platelet aggregation and prolonged bleeding times of the Greenland
Eskimos suggested an important mechanism by which n-3 PUFA could affect CHD
(Dyerberg et al., 1978). Early studies of the nuits highlighted their
lower coronary mortality compared to their Danish counterparts. Their diet
included a strikingly high intake of n-3 PUFAs. This resulted in lower blood
cholesterol, lower TAG, lower LDL- and VLDL-cholesterol, increased
HDL-cholesterol, increased bleeding times, and lower rates of CHD (Kromhout
et al., 1985; Shekelle et al., 1985; Dolecekand Grandits,
1991; Kromhout et al., 1995). These effects have been seen better in
women (Iso et al., 2001).

In the fish under
investigation cholesterol is quite high in the flesh except in the breeding
season when it was not detected. But the average consumable cholesterol of the
fish which is around 155mg is far less than the recommended dietary intake of
cholesterol of <200mg (Kris-Etherton et al., 2003). The contribution
of dietary SAFA to serum Total Cholesterol (TC) is far greater and is almost
ten times that of dietary cholesterol (Enas et al.,2003).
Although many affluent Indians consume 50% of energy from fat mainly from the
cooking medium of vegetable ghee, which has a load of transunsaturated fatty
acids (TRAFA), and fatty fish and meat, most of the average Indians consume
20%-25% of energy from fat.

This fish can be safely
recommended as it has low SAFA and high PUFA and MUFA. The SAFA/UFA ratios are
below 1 in the pre-breeding and in the post-breeding seasons while in the
breeding season it is marginally high. Enas (1996) showed that SAFA raises the
serum TC level thrice as much as PUFA does, and MUFA lowers it. Most of this
increase is due to an increase in LDL. Some increase in HDL also is registered
but is not sufficient to offset the atherogenicity and thrombogenicity
resulting from marked elevation of LDL. The AI and TI of the fish are low
indicating low LDL. Stearic acid (18:0) is desaturated to oleic acid (18:1n-9) soon
after its absorption and so dose not raise the TC level (Bonanome and Grundy, 1988;
Denke and Grundy, 1992). In the fish oleic acid (18:1n-9) is in good quantity
while stearic acid (18:0) is present substantially, therefore, the fish can be
recommended.

It is to be mentioned
that fishes have the unique capability of metabolising fats readily and, as a
result can stay for long periods of time under conditions of food deprivation.
This is reflected very well in this fish. 
The n-3/n-6 ratios once again prove that this lean fish may be
classified as Type II (Takeuchi, 1996).

The high carbohydrate
diet very common in the Indian families has its positive roles but it is also
associated with highly atherogenic VLDLs. So a complementary of a fish like C.
punctatus in the diet would be more effective in preventing CAD amongst
Indians who have a high prevalence of this metabolic syndrome and diabetes.