*Correspondence author: Absar Alam, Regional Centre, ICAR-Central Inland Fisheries Research Institute, 24-Panna Lal Road, Allahabad, Uttar Pradesh, India
How to cite this article:Absar A, Vaisakh G, Dharma N J, Kripal D J, Jeetendra K, et al. Food and Feeding Biology of Commercially Important FreshwaterEel, Mastacembelus Armatus (LACEPÈDE, 1800) from the Ganga River, India. Oceanogr Fish Open Access J. 2020; 11(4): 555819. DOI: 10.19080/OFOAJ.2020.11.555819
Food and feeding biology of freshwater zig-zag eel Mastacembelus armatus (LACEPÈDE, 1800) was investigated from the Allahabad waters of the river Ganga from April 2015 to March 2016. The Stomach contents of 326 individuals of M. armatus were collected monthly from the Daraganj fish landing centre located on the bank of the river Ganga. The composition of food content was expressed as percentage of the frequency of occurrence (%Oi) and percentage of the volume (Vi). The main food items were estimated by Index of preponderance (Ii). The three major food items of M. armatus were the small sized teleosts, insects, and molluscs. The analyses of the relative gut length (RGL) revealed it carnivorous type of feeding habit. The Gastro-Somatic Index (GaSI) in the male and female ranged between 2.65 and 4.41 with a mean of 3.42 ± 0.09 and 2.84 and 3.43 with a mean value of 3.05 ± 0.03. The mean GaSI value differed significantly at 5% level of significance (F = 6.72, p = 0.01) in both the male and female indicated significant variation in the feeding habits between both the sexes. This study furnishes baseline information on the food and feeding habits of M. armatus which could be useful in formulation of the management and conservation strategies of this species in the region.
Keywords: Diet composition Gastro-somatic index Index of preponderance Relative gut length Zig-zag eel
M. armatus commonly (Lacepede, 1800), known as zig-zag eel forms an important fishery in the river Ganga [1,2]. It is found to occur in India, Bangladesh, Pakistan, Sri Lanka, Nepal, Burma through Thailand and Malaysia to Southern China [1,3]. It is locally known as Bam or Gend along the stretches of the river Ganga. It is distributed between Haridwar and Hooghly stretch of the River Ganga. It is usually found in wetlands, reservoirs, streams, and rivers with the substrate that is sandy, pebbly or boulder. It is caught mainly by hook and line and gill nets.
M. armatus occurs below the top predators in the food chain and plays a vital role in the freshwater ecosystem as an intermediate predator in maintaining the equilibrium of the structure and ecology of the regional freshwater communities. Overfishing, invasion of exotics, habitat degradation, climate change coupled with pollution have resulted in the population decline of indigenous fish species in the Ganga River [4-10].
Over-exploitation of M. armatus may negatively impact the whole
fisheries that can result in a trophic cascade of the immediate trophic levels. M. armatus, the freshwater spiny eel is a major demersal finfish resource inhabiting the inland tropical and subtropical freshwater and brackish water bodies in Asia. Even though it is widely distributed in the Asian continent, there is a little published information on the food and feeding habits of M. armatus [11-15].
Examination of the gut content is commonly employed to investigate the composition of food intake and feeding habits [8,14,15]. Dietary analysis is widely used in food web ecology and in designing trophic models of fishes for understanding relationships in the aquatic communities in the complex ecosystems . In order to understand the ecological worth of this species, it is crucial to study the food and feeding habits of M. armatus from the different geographical locations around theglobe. Therefore, the present study was carried out to investigate
the diet composition and dietary habits of M. armatus in the River
Ganga of north India.
A total of 286 samples of M. armatus comprising 167 males
and 119 females were collected biweekly from the Daraganj
fish landing centre located on the bank of the river Ganga at
Allahabad (Figure 1), early in the morning for over 12 months.
The fish samples collected were immediately kept in an insulated
icebox and transported to the laboratory of Allahabad Regional
Centre of Central Inland Fisheries Research Institute (CIFRI, Uttar
Pradesh, India). Sexes were noted only after taking total length
(TL) and total body weight (W) to the nearest 0.5 cm and 0.1 g
by dissection in the laboratory. The gut length (nearest mm), as
well as gut-weight (nearest 0.01 g), were recorded separately for
males and females, respectively and preserved in 5 % formalin,
for subsequent analysis. The prey items in the gut content were
identified to the lowest possible taxonomic level employing various
identification guides. Stereo-zoom microscope (Nikon SMZ 745T)
was used whenever necessary for the identification of the prey
items. The gut content of the individual fish was categorised into
major groups such as teleosts, insects, crustaceans, molluscs and
digested organic matter.
The percentage occurrence of each major group of items
was calculated by multiplying the ratio of the number of times
the major group of item occurrence to the total number of guts
analysed by a hundred. The percentage volume of each major
group of food items was estimated by point method . The
Index of preponderance (I) for each food items were computed
based on the total occurrence of all food items during the various
months and then ranked accordingly . Bodyweight (W) - gutweight
(w) and body weight (W) – gut length (L) relationships
were established following formula given by Le Cern in1951
 as w = aWb and L = aWb where a and b are intercepts and
regression coefficients of the functional regression between W
and w & L and w and after logarithmic transformation has the
form of Log w = a + blog W and Log L = a + b log W, respectively
The relative length of the gut (RGL) as ratio of total gut length to
total length was worked out to analyse its feeding habit. Feeding
intensity was estimated based on the Gastro-somatic index (Ga-SI
= Weight of the gut (w)/Body weight (W) x100). The analysis of
variance (ANOVA) was done for parameters RGL and GaSI to test
their monthly significant differences at a 5% level of significance
employing SAS software (ver.9.3). The multiple comparisons were
done using Tukey’s test.
Data from 286 individuals of M. armatus containing 167 males
and 119 females were examined. The total length (TL) and body
weight (W) ranged from 230 to 600 mm, 25-373 g with mean of
409.20 ± 5.38 mm and 156.07 ± 5.26 g in male while in females it
ranged from 230 to 630 mm, 29 to 446 g with mean of 386.86 ±
5.17 mm and 142.63 ± 5.39 g, respectively. The various food items,
their percentage composition (by of volume and occurrence) and
Pondreal index observed in the gut of M. armatus are depicted in
table 1. Around 39% of all the guts observed for the gut content
analysis were empty and maximum percentage was found
between July and October. The small-sized teleosts formed the
main food item of the gut content forming 37.37 % volume and30.65 % by occurrence. The major fish genera observed were
Barilius, Aspidoparia, Salmophasia, Gudusia, Gonialosa, Chela,
Sicamugil, etc. The insects were next principal food item in the
diet constituting around 23.04% and 24.12% by volume and
The dominant genera observed among the insects were the
dipteran larvae, the Chironomous followed by the dragonfly
nymph. The molluscs mainly small-sized formed the next
important food item in the gut comprising 17.03% by volume and
17.09% by occurrence. Among the molluscs, the abundant genera
were Bellamya and Corbicula and their larvae. The digested
organic matter formed the next dominant food item in the diet
forming around 15.07% by volume and 14.57% by occurrence.
The crustaceans constituted by small-sized shrimps and crabs
were the next important group of the food item observed in
the gut of M. armatus forming 6.57% by volume and 8.54% by
occurrence. Annelids constituted only 0.91% by volume and
5.03% by occurrence. The observation of bottom dwellers (smallsized
mollusc and shrimps) in the gut content suggested it to
be the bottom feeder. Since the major prey organism included
nektonic organism (teleosts), it seemed that M. armatus does not
feed exclusively on benthic food organisms but also on the prey
organism from the water column.
The higher frequency of occurrence and percentage of the
volume of teleosts, insects, molluscs and crustaceans in the diet
suggested that the feeding habit of the fish was carnivorous. Sand
and mud were not recorded in the stomach content agreed with
the observations [12,14]. The gill rackers are absent in spiny eels
 which might have influenced the feeding habit as no plant
matter was witnessed in the diet of the M. armatus. A wide variety
of prey organisms of considerable size ranges recorded in the
diet were mostly swallowed in their entire form as it lacks the
masticating apparatus  to grind the consumed food items,
suggested active searching of the environment for its live prey
organisms. For the pooled data, RGL value ranged from 0.29 to
0.92 with a mean of 0.64 ± 0.003 and varied in different months.
The ANOVA test showed that there was a significant difference
between both the sexes (p=6.32, p= 0.0125). The mean RGL values
also differed significantly in different month in male (F = 2.89, p =
0.0017) and female (F=2.13, p=0.027) at 5% level of significance
These difference in the feeding might be due to the variations
in the available diet in the wild or differences in their sizes and
biological factors (maturity stages, GaSI, etc.). Dasgupta in 2004
observed the average RGL value for carnivorous fishes as 0.70
. In the present study, the observed RGL ranged between 0.6
and 0.67 with a mean of 0.64 ± 0.003 was in concurrence with
the study of Serajuddin and Mustafa . This also indicated that
the feeding habit of the fish to be carnivorous, agreed with the
earlier studies [11, 12,14]. The mean monthly Gastro-Somatic
Index (GaSI) in the male and female ranged between 2.65
and 4.41 with a mean of 3.42 ± 0.09 and 2.84 and 3.43 with an
average value of 3.05 ± 0.03 (Figure 3). There was a significant
difference between the male and female GaSI at 5% level of
significance (F=6.72, p = 0.01), suggested that both the sexes did
not feed with equal intensity. The monthly mean GaSI was found
to be insignificant between the months in the female (F=1.84, p=
0.0562) while significant in the male (F=4.23 p=0.0001) at 5%
level of significance .
The analysis of GaSI showed variation between the months
in male suggested that feeding intensity oscillated round the
year. The male showed significantly higher feeding intensity than
female as they spent lesser energy in the reproductive process.
The feeding intensity of M. armatus was observed to be high as
69% of total guts examined contained food items which were
contrary to the report that high percentage of the empty stomachs
were observed in the carnivorous fishes [12,14,21,22]. This
indicated that the preferred food items were available in plenty in
the habitat. In the month of April, July and October, low GaSI was
observed in the female. This low intensity of feeding may be due
to the stress during peak spawning months when GSI values were
high [8,15]. The relationship between the body weight (W) and
total gut-weight (w) was calculated using the linear regression as:
w = 1.116163 + 0.024406W (R2 = 0.51). The relationship between
body weight (W) and gut length (L) was estimates as L = 17.78146
+ 0.048847W (R2= 0.623748). Both the relationships were found
to be highly significant (p< 0.05) and suggested that gut weight
and gut length varied with body weight. This variation was more
for gut length than gut-weight as b for body weight-gut length was
more than the body weight and gut-weight relationships.
The present investigation was undertaken to examine the
dietary composition and feeding habits of M. armatus from the
river Ganga at Allahabad. It fed on a wide variety of food items
which were categorized into six distinctive groups viz. teleosts,
insects, molluscs, crustaceans, annelids and digested organic
matter of animal origin suggested its carnivorous feeding habit.
Teleosts were the most preferred food items followed by insects,
small-sized molluscs, crustaceans, etc., respectively. M. armatus,
an economically important fish with food as well as ornamental
value in inland fisheries has the potential for fish diversification
and domestication in Asian countries. It is henceforth suggested
that additional investigations on other aspects of the biology of
this fish species are needed for its successful aqua farming. In the
meantime, in situ experiments on the nutritional requirements of
this fish can be conducted from the wild collection of juveniles and
fingerlings to evaluate its domestic potential. This investigation
provides baseline information on the food and feeding habits
of M. armatus, which would be useful in the management and
conservation of this species in the region.
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