Biomarkers
Introduction
Ray, an abundant fish among the many species caught off the Mauritanian coast, is only used locally. As no fatty acid profiles have been
reported for the beef ray Rhinoptera marginata, we conducted a comparative chemical study of lipids [total (TL), neutral (NL) and polar lipids
(PL)] from this species in order to evaluate possible variations relating
to sex and a given organ such as muscle, liver and gonads. Our intention
was to improve the commercial development of this fish.
Material and methods
Specimens of R. marginata caught off the Mauritanian coast (up to Cape
Camaris) at depths of 9 m to 27 m in July, August and September
1996 and 1997 were purchased at local fish markets. The fish weighed
between 750 g and 900 grammes. Total lipids were extracted with
chloroform-methanol (Bligh & Oyer, 1959). The separation of total
lipids mto NL and PL was performed by flash chromatography on a
short silica gel column (Still et al., 1978), using diethyl ether (NL) and
methanol (PL) as successive eluents. Monoglyceride was taken as a
reference for the separation between NL and PL. Methyl esters were
obrained as usually and then converted into pyrrolidide derivatives
(pyrrolidine-acetic acid). The different fatty acid derivatives were
analysed by GC/MS on an HP 5890 DB-1 (30 m x 0.3 mm, 180°C to
300°C, 3°C/min) linked to an HP5989A mass spectrometer (70eV).
Results and discussion
Total lipids accounted for 20 to 40% in liver and gonads and 8% in
muscle (fresh weight), although the muscle value was as low as 0.1%
for fresh females. As shown in the table, NL were more abundant than
PL, except for male gonads (64% PL) and to a lesser extent male muscle
(37%). As shown, saturated acids were the predominant fatty acids in
all lipid fractions, especially in NL. Arachidonic acid amounted to 10%
and 6% respectively in male and female muscles. The 20:5 (n-3) acid
accounted for about 10% of NL in male and female organs and occurred in low amounts or not at all in PL. The 22:6 (n-3) acid accounted
for 3.5-6.3% in all fractions, except for NL from male gonads (11%)
and PL from female organs (2% or not at all).
Lipid content of Rhinoptera marginata.
Male
Female
Liver
Gonads
Mnscle
Liver
Gonads
Muscle
NL
97.1
35.5
63.0
97.5
94.2
84.6
PL
2.9
64.5
37.0
2.5
5.0
15.4
51
Introduction
Ray, an abundant fish among the many species caught off the Mauritanian coast, is only used locally. As no fatty acid profiles have been
reported for the beef ray Rhinoptera marginata, we conducted a comparative chemical study of lipids [total (TL), neutral (NL) and polar lipids
(PL)] from this species in order to evaluate possible variations relating
to sex and a given organ such as muscle, liver and gonads. Our intention
was to improve the commercial development of this fish.
Material and methods
Specimens of R. marginata caught off the Mauritanian coast (up to Cape
Camaris) at depths of 9 m to 27 m in July, August and September
1996 and 1997 were purchased at local fish markets. The fish weighed
between 750 g and 900 grammes. Total lipids were extracted with
chloroform-methanol (Bligh & Oyer, 1959). The separation of total
lipids mto NL and PL was performed by flash chromatography on a
short silica gel column (Still et al., 1978), using diethyl ether (NL) and
methanol (PL) as successive eluents. Monoglyceride was taken as a
reference for the separation between NL and PL. Methyl esters were
obrained as usually and then converted into pyrrolidide derivatives
(pyrrolidine-acetic acid). The different fatty acid derivatives were
analysed by GC/MS on an HP 5890 DB-1 (30 m x 0.3 mm, 180°C to
300°C, 3°C/min) linked to an HP5989A mass spectrometer (70eV).
Results and discussion
Total lipids accounted for 20 to 40% in liver and gonads and 8% in
muscle (fresh weight), although the muscle value was as low as 0.1%
for fresh females. As shown in the table, NL were more abundant than
PL, except for male gonads (64% PL) and to a lesser extent male muscle
(37%). As shown, saturated acids were the predominant fatty acids in
all lipid fractions, especially in NL. Arachidonic acid amounted to 10%
and 6% respectively in male and female muscles. The 20:5 (n-3) acid
accounted for about 10% of NL in male and female organs and occurred in low amounts or not at all in PL. The 22:6 (n-3) acid accounted
for 3.5-6.3% in all fractions, except for NL from male gonads (11%)
and PL from female organs (2% or not at all).
Lipid content of Rhinoptera marginata.
Male
Female
Liver
Gonads
Mnscle
Liver
Gonads
Muscle
NL
97.1
35.5
63.0
97.5
94.2
84.6
PL
2.9
64.5
37.0
2.5
5.0
15.4
51