Mustafa-Kamal, A.S., I.S. Kamaruddin, A. Christianus, S.K. Daud, and L. Yu-Abit,. 2012. Feeding habits of fishes in the Pengkalan Gawi-Pulau Dula section of Kenyir Lake Terengganu, Malaysia. Asian Fisheries Science Journal. Asian Fisheries Society. 25:144-157.
The journal link: http://www.asianfisheriessociety.org/publication/abstract.php?id=14
MUSTAFA-KAMAL,
A.S.1, I.S.
KAMARUDDIN1*, A.
CHRISTIANUS1, S.K. DAUD2 and L. YU-ABIT3
1Department of Aquaculture,
Faculty of Agriculture, Universiti Putra Malaysia, 43400, UPM Serdang,
Selangor,
Malaysia.
2Department of Biology, Faculty of
Science, Universiti Putra Malaysia, 43400, UPM Serdang, Selangor, Malaysia.
3UPM Holdings Sdn. Bhd., 43400,
UPM Serdang, Selangor Malaysia.
Abstract
A
study was conducted to determine the feeding habits of the fish in the
Pengkalan Gawi–Pulau Dula section of Kenyir Lake, Terengganu, Malaysia. Fish
were collected on a monthly basis from February 2008 to January 2009 and their
stomach contents were identified and quantified. A total of 261 individual fish
from 6 different species were captured and the sample size of each species
ranged from between 10 to 98 individuals. Aquatic insects were the most abundant
among food items consumed. Four species namely, Barbodes schwanenfeldii (Bleeker,
1853), Notopterus sp., Hampala macrolepidota, Kuhl and van
Hasselt, 1823, and Pristolepis fasciatus (Bleeker, 1851) were classified
as omnivorous species, whereas Hemibagrus nemurus (Valenciennes, 1840)
was classified as insectivorous and Channa micropeltes (Cuvier, 1831)
was classified as piscivorous. The feeding habits of the three most dominant
species were found to differ spatially and temporally. A more complex feeding
habit was observed in the Pulau Pupi station and changes in feeding guilds were
observed at each season throughout the study period.
Introduction
Freshwater fish catches including
those from reservoirs in Malaysia have declined over the past few years. According to
Ambak and Jalal (2006), the fish stocks in reservoirs, in general, are in a state of decline and a concerted effort is required to maintain exploitable resources at a sustainable level. Khoo et al.
(1987) observed that Malaysian inland capture fisheries was principally dominated by
cyprinids and silurid fish species especially in large rivers and lake systems, and sharp declines in
catches were recorded during recent decades. These declines can be attributed to a number of
factors, which include pollution, siltation, dam construction, illegal mass fishing methods as well as
overfishing (Khoo et al. 1987).
Recently, freshwater reservoir
fishery was recognised by the Malaysian government as an important sector which deserves
special attention for development. In order to manage and conserve freshwater fish
resources, it is important to gather basic information on the fish community in the area. The key
factor is to understand both the biological and fundamental processes of individual fish species, which includes
the knowledge of their feeding habits.
Kenyir Lake in Malaysia requires
serious management attention for the conservation of its fishery resources. This lake,
which lies at latitude 4° 41’ N and longitude 102° 40’ E., is currently the biggest man-made
lake in Malaysia with a surface area of about 36,900 ha. The average depth of the lake is 37
m; however, the maximum depth is 145 m. There are 340 islands in the lake, more than 14
waterfalls and numerous rapids and rivers.
In 1995, Jackson and Marmulla
(2001) reported that the annual fish catch in Kenyir Lake was 720 tonnes.year-1. Recent data in
2010 updated by the DOF (2010), however, showed a reduced catch of 58.58 tonnes.year-1. The fish
production of Kenyir Lake is declining and monitoring is needed to manage
the lake ecosystem. Detailed studies on the feeding habits of fish in Kenyir Lake are lacking too.
Therefore, this study was undertaken to determine the feeding habits of Barbodes
schwanenfeldii (Bleeker, 1853), Notopterus sp., Hampala
macrolepidota,Kuhl and van Hasselt, 1823, Hemibagrus
nemurus (Valenciennes, 1840), Channa micropeltes (Cuvier, 1831) and Pristolepis
fasciatus (Bleeker, 1851) in the Pengkalan Gawi–Pulau Dula section of Kenyir Lake. The
findings are expected to provide some useful inputs for fishery management and conservation
programmes in the Kenyir Lake.
Materials
and Methods
The study was conducted at the
Pengkalan Gawi–Pulau Dula section of Kenyir Lake which extends from Pengkalan Gawi
(Gawi Jetty) in the north to Pulau Dula (Dula Island) in the south and lies between 5°03’ N to
5°08’ N, and 102°44’ Eto 102°52’ E (Fig. 1). The section is only a small part of the lake
which covers an area of about 30 km2. The section is located at the main entrance – visitor’s access
to the Lake where a boat jetty is located. Fish were sampled monthly from February 2008 to
January 2009 at three stations in the lake. These stations were designated as Station A (Pulau
Dula), Station B (Sungai Ikan) and Station C (Pulau Pupi). Station A (Pulau Dula) is located
at Dula Island where the littoral zone is covered with submerged dead tree trunks that
emerge from the lake’s water surface. Station B (Sungai Ikan) is situated at the river mouth of
Sungai Ikan where water from that river flows into the lake, while Station C (Pulau Pupi) is located near the Pupi
Island and has a very steep and deep littoral zone.
Fig
1. Maps showing sampling stations at the Pengkalan Gawi–Pulau Dula
section of Kenyir Lake Terengganu.
Fish samples were
collected by using gill nets of various mesh sizes (5.08, 6.35 and 7.62 cm). All fish caught
were identified using keys from Mohsin and Ambak (1983). The stomach of each fish was removed
and preserved in sample bottles containing a 5% formalin solution. In the laboratory, these
stomach contents were weighed and were taxonomically identified and counted. The fish feeding
habit indices used in this study are as follows: 1) percentage composition of food items (CFI), 2)
frequency of occurrence of food items (FOFI) and 3) trophic level.
Percentage
composition of food items (CFI)
The CFI method was
used to measure the food composition that was present in every stomach and the total
was expressed as a percentage of the total number of food items found.
[1]
CFI (%) = (Number of food A item occurring / Total number of food items
sampled) x 100
Frequency
of occurrence of food items (FOFI)
The FOFI method was
used for recording the number of stomachs containing one type of food item and the
total was expressed as a percentage of the total number of stomachs examined.
[2]
FOFI (%) = (Total number of stomachs containing food item A / Total number
stomachs examined) x 100
Trophic level
The trophic level of individual
fish was performed using the Troph-Lab computer programme which was introduced
and developed by ICLARM-FAO (Pauly et al. 2000). The equation is as below:
[3] TROPHIC
LEVEL =1+ΣDCij x TROPHj
Results
A total of 261 individuals
belonging to 6 fish species were analysed for feeding data. The number of individual fish ranged
from 10 individuals for P. fasciatus to 98 individuals for B. schwanenfeldii. Altogether,
four species of fish namely B. schwanenfeldii, Notopterus sp., H. nemurus and P.
fasciatus consumed aquatic insects as the main food item. Food consisting
of fish items dominated the diets of
H. macrolepidota and C. micropeltes. Plant material although not the most abundant food item
found in the stomachs of any of the fish species sampled, was present in the stomachs of all
six species (Table 1).
In terms of the trophic level,
the values for all species ranged from 2.74±0.36 for P. fasciatus to 3.56±0.63 for
C. micropeltes (Table 1). Four species were categorised as omnivorous species due to values less than
3. These were B. schwanenfeldii, Notopterus sp., H. macrolepidota and P.
fasciatus. Meanwhile H. nemurus and C. micropeltes were
categorised as predators.
For B. schwanenfeldii,
although the percentage composition of aquatic insects in the stomach was high (62.7%), the
percentage of occurrence of aquatic insects amongst these samples was relatively low
(22.5%). The other food item that was abundant in the diet of B. schwanenfeldii was plant
material comprising 16.9% of the total food items consumed and an estimated 22.1% of the total guts
examined. This species was classified as omnivorous where both animal and plant origins of
food items were consumed in equal amounts.
The percentage composition of
aquatic insects consumed by Notopterus sp. was 64.6% from the total guts examined.
Subsequently, about 14.8% of stomachs were found to contain plant material and 14.5% of
stomachs were found to contain detritus as the other component of the diet of this species. Notopterus
sp. was also the only species in this study which was found to consume all of the food items
classified. Overall, this species was classified as an omnivorous species with trophic level of 2.86±0.34.
Table 1. Percentage
composition of food items (%CFI), Frequency of occurrence of food items (%FOFI)
and trophic level for the six most
dominant species in Pengkalan Gawi–Pulau Dula Section of Kenyir Lake from February 2008 to January 2009.
Species
|
Food
item
|
%CFI
|
%FOFI
|
|
B.
schwanenfeldii
|
Fish
|
0.1
|
0.7
|
|
(Trophic
level: 2.85±0.33)
|
Aquatic
insect
|
62.8
|
22.5
|
|
(n=
98)
|
Molluscs
|
3.0
|
3.6
|
|
Crustaceans
|
-
|
-
|
||
Plant
Materials
|
16.9
|
22.1
|
||
Detritus
|
2.1
|
6.1
|
||
Copepods
|
2.2
|
6.4
|
||
Cladocerans
|
1.3
|
5.0
|
||
Rotifer
|
1.5
|
5.0
|
||
Bacillariophyta
|
3.2
|
8.2
|
||
Chlorophyta
|
3.2
|
9.3
|
||
Euglenophyta
|
0.8
|
3.6
|
||
Cyanophyta
|
2.3
|
5.7
|
||
Unidentified
|
0.6
|
1.8
|
||
Notopterus
sp.
|
Fish
|
0.9
|
2.2
|
|
(Trophic
level: 2.86±0.34)
|
Aquatic
insect
|
64.6
|
21.6
|
|
(n=
75)
|
Molluscs
|
0.1
|
0.9
|
|
Crustaceans
|
2.3
|
7.7
|
||
Plant
Materials
|
13.3
|
14.8
|
||
Detritus
|
7.2
|
14.5
|
||
Copepods
|
0.7
|
3.4
|
||
Cladocerans
|
1.6
|
3.4
|
||
Rotifer
|
1.1
|
3.7
|
||
Bacillariophyta
|
1.9
|
4.9
|
||
Chlorophyta
|
1.5
|
5.2
|
||
Euglenophyta
|
0.5
|
3.1
|
||
Cyanophyta
|
1.5
|
4.0
|
||
Unidentified
|
2.8
|
10.5
|
||
H.
macrolepidota
|
Fish
|
24.3
|
31.3
|
|
(Trophic
level: 2.96±0.47)
|
Aquatic
insect
|
13.5
|
14.1
|
|
(n=
44)
|
Molluscs
|
1.0
|
1.6
|
|
Crustaceans
|
7.8
|
7.8
|
||
Plant
Materials
|
7.8
|
9.4
|
||
Detritus
|
8.7
|
14.1
|
||
Copepods
|
4.9
|
6.3
|
||
Cladocerans
|
-
|
-
|
||
Rotifer
|
-
|
-
|
||
Bacillariophyta
|
8.7
|
4.7
|
||
Chlorophyta
|
14.6
|
4.7
|
||
Euglenophyta
|
1.0
|
1.6
|
||
Cyanophyta
|
5.8
|
1.6
|
||
Unidentified
|
1.9
|
3.1
|
||
H. nemurus
|
Fish
|
3.4
|
11.4
|
|
(Trophic
level: 3.11±0.41)
|
Aquatic
insect
|
77.0
|
38.6
|
|
(n=
22)
|
Molluscs
|
-
|
-
|
|
Crustaceans
|
7.5
|
20.5
|
||
Plant
Materials
|
2.9
|
11.4
|
||
Detritus
|
7.5
|
13.6
|
||
Copepods
|
-
|
-
|
||
Cladocerans
|
-
|
-
|
||
Rotifer
|
-
|
-
|
||
Bacillariophyta
|
-
|
-
|
||
Chlorophyta
|
-
|
-
|
||
Euglenophyta
|
-
|
-
|
||
Cyanophyta
|
-
|
-
|
||
Unidentified
|
1.7
|
4.5
|
||
C.
micropeltes
|
Fish
|
62.5
|
71.4
|
|
(Trophic
level: 3.56±0.63)
|
Aquatic
insect
|
-
|
-
|
|
(n=
12)
|
Molluscs
|
-
|
-
|
|
Crustaceans
|
-
|
-
|
||
Plant
Materials
|
37.5
|
28.6
|
||
Detritus
|
-
|
-
|
||
Copepods
|
-
|
-
|
||
Cladocerans
|
-
|
-
|
||
Rotifer
|
-
|
-
|
||
Bacillariophyta
|
-
|
-
|
||
Chlorophyta
|
-
|
-
|
||
Euglenophyta
|
-
|
-
|
||
Cyanophyta
|
-
|
-
|
||
Unidentified
|
-
|
-
|
||
P.
fasciatus
|
Fish
|
0.9
|
3.2
|
|
(Trophic
level: 2.74±0.36)
|
Aquatic
insect
|
37.9
|
22.6
|
|
(n=
10)
|
Molluscs
|
9.5
|
6.5
|
|
Crustaceans
|
-
|
-
|
||
Plant
Materials
|
0.9
|
3.2
|
||
Detritus
|
0.9
|
3.2
|
||
Copepods
|
6.0
|
6.5
|
||
Cladocerans
|
1.7
|
3.2
|
||
Rotifer
|
1.7
|
6.5
|
||
Bacillariophyta
|
15.5
|
16.1
|
||
Chlorophyta
|
12.1
|
12.9
|
||
Euglenophyta
|
2.6
|
6.5
|
||
Cyanophyta
|
10.3
|
9.7
|
||
Unidentified
|
-
|
-
|
Pristolepis
fasciatus was
also classified as an omnivorous species that consumed mostly aquatic insects (37.9%) and
phytoplankton (40.5%). It was the only species that fed on a high volume of molluscs (snails) which
comprised 9.5% of the stomach contents. On
the other hand, although H. macrolepidota was
frequently found to consume fish, it was still classified as an omnivorous species. This is due
to the equal proportion of animal and plant material food items consumed, with a total of 51.5%
and 49.5% of the total composition respectively.
The trophic value for H.
nemurus was 3.11±0.41. It was therefore categorised as an insect feeder with a diet consisting of
77.0% aquatic insects in the stomach. Meanwhile, C. micropeltes was numerically the most
representative with fish prey food items at 62.5%. Therefore, this species was grouped under the category
of fish predator or piscivorous species.
Spatial feeding
habits of fish
The feeding habits of the three
most dominant species of fish namely B. schwanenfeldii, Notopterus sp. and H.
macrolepidota were determined through the analysis of spatial data. These species were chosen due to their
abundance at each station throughout the sampling period from February 2008 to January 2009.
The trophic value for Notopterus
sp. showed that it was omnivorous at all stations,whereas B. schwanenfeldii was
omnivorous in Pulau Dula and Sungai Ikan but was herbivorous in Pulau Pupi. The highest value
for B. schwanenfeldii (2.91±0.35) was recorded in Sungai Ikan and for Notopterus sp.
(2.88±0.36) in Pulau Pupi. This differed when compared to H. macrolepidota which was determined
to be omnivorous in Sungai Ikan but was found to be carnivorous in Pulau Dula and
Pulau Pupi (Table 2). Different kinds of feeding habits in different stations were also observed.
In Pulau Dula, fish were
omnivorous and carnivorous. Barbodes schwanenfeldii and Notopterus sp. at this
station were classified as omnivorous whereas H. macrolepidota fed
solely on crustaceans (shrimp) and was
thus categorised as a shrimp predator species. On the other hand, the only feeding type
identified in Sungai Ikan station was omnivorous.
Three feeding types were observed
in Pulau Pupi (omnivorous, herbivorous and carnivorous). The feeding habit
of Notopterus sp. in this station was omnivorous, similar to Notopterus sp. at the Pulau
Dula and Sungai Ikan stations. Barbodes schwanenfeldii at this station meanwhile differed in
comparison to the other stations as they consumed mainly plant material (64.8%) and thus was
categorised as a herbivore. The only species categorised as carnivorous was H.
macrolepidota which consumed mainly aquatic insects and fish prey food items (25.5% each) (Table 2).
Table 2. The percentage
composition of food items (%CFI) and frequency of occurrence of food items
(%FOFI) of the three most dominant species at each station
during the study period.
Station
|
Food
item
|
B.schwanenfeldii
|
Notopterus
sp.
|
H.
macrolepidota
|
||||
%CFI
|
%FOFI
|
%CFI
|
%FOFI
|
%CFI
|
%FOFI
|
|||
Pulau
|
Fish
|
0.1
|
0.7
|
-
|
-
|
-
|
-
|
|
Dula
|
Aquatic
insect
|
62.6
|
24.8
|
57.1
|
20.0
|
-
|
-
|
|
(A)
|
Molluscs
|
5.7
|
3.3
|
1.3
|
6.7
|
-
|
-
|
|
Crustaceans
|
-
|
-
|
-
|
-
|
100.0
|
100.0
|
||
Plant
Materials
|
11.9
|
19.3
|
11.7
|
19.9
|
-
|
-
|
||
Detritus
|
1.0
|
3.3
|
16.9
|
20.0
|
-
|
-
|
||
Copepods
|
2.2
|
6.7
|
-
|
-
|
-
|
-
|
||
Cladocerans
|
1.0
|
3.3
|
-
|
-
|
-
|
-
|
||
Rotifer
|
2.5
|
7.3
|
1.3
|
6.7
|
-
|
-
|
||
Bacillariophyta
|
4.5
|
9.3
|
-
|
-
|
-
|
-
|
||
Chlorophyta
|
3.8
|
11.3
|
1.3
|
6.7
|
-
|
-
|
||
Euglenophyta
|
0.8
|
3.3
|
-
|
-
|
-
|
-
|
||
Cyanophyta
|
3.8
|
6.7
|
3.9
|
6.7
|
-
|
-
|
||
Unidentified
|
0.1
|
0.7
|
6.5
|
13.3
|
-
|
-
|
||
Trophic
Level
|
2.91±0.37
|
2.78±0.32
|
3.37±0.58
|
|||||
Sungai
|
Fish
|
0.1
|
1.1
|
1.1
|
2.5
|
23.5
|
40.0
|
|
Ikan
|
Aquatic
insect
|
71.7
|
19.2
|
64.8
|
21.7
|
2.0
|
4.0
|
|
(B)
|
Molluscs
|
0.3
|
2.1
|
0.1
|
0.8
|
-
|
-
|
|
Crustaceans
|
-
|
-
|
2.7
|
9.4
|
5.9
|
8.0
|
||
Plant
Materials
|
13.5
|
23.4
|
15.7
|
16.0
|
3.9
|
8.0
|
||
Detritus
|
2.3
|
6.4
|
6.2
|
13.9
|
7.8
|
16.0
|
||
Copepods
|
1.4
|
5.3
|
0.6
|
2.5
|
-
|
-
|
||
Cladocerans
|
1.5
|
7.4
|
1.5
|
3.3
|
-
|
-
|
||
Rotifer
|
0.8
|
3.2
|
0.8
|
3.7
|
-
|
-
|
||
Bacillariophyta
|
2.6
|
9.6
|
1.5
|
4.9
|
17.6
|
12.0
|
||
Chlorophyta
|
2.7
|
8.5
|
1.3
|
4.5
|
25.5
|
4.0
|
||
Euglenophyta
|
1.0
|
5.3
|
0.6
|
3.3
|
2.0
|
4.0
|
||
Cyanophyta
|
1.4
|
6.4
|
0.9
|
3.3
|
11.8
|
4.0
|
||
Unidentified
|
0.8
|
2.1
|
2.2
|
10.2
|
-
|
-
|
||
Trophic
Level
|
2.91±0.35
|
2.87±0.35
|
2.68±0.40
|
|||||
Pulau
|
Fish
|
-
|
-
|
0.2
|
1.6
|
25.5
|
26.3
|
|
Pupi
|
Aquatic
insect
|
11.9
|
22.1
|
65.0
|
20.3
|
25.5
|
21.0
|
|
(C)
|
Molluscs
|
3.1
|
8.3
|
-
|
-
|
2.0
|
2.6
|
|
Crustaceans
|
-
|
-
|
1.0
|
3.1
|
7.8
|
5.3
|
||
Plant
Materials
|
64.8
|
30.6
|
4.5
|
9.4
|
11.8
|
10.5
|
||
Detritus
|
7.0
|
16.7
|
9.2
|
15.6
|
9.8
|
13.2
|
||
Copepods
|
7.0
|
8.3
|
1.5
|
7.8
|
9.8
|
10.5
|
||
Cladocerans
|
2.3
|
5.6
|
2.5
|
4.7
|
-
|
-
|
||
Rotifer
|
-
|
-
|
2.2
|
3.1
|
-
|
-
|
||
Bacillariophyta
|
-
|
-
|
3.7
|
6.3
|
-
|
-
|
||
Chlorophyta
|
2.3
|
2.8
|
2.0
|
7.8
|
3.9
|
5.3
|
||
Euglenophyta
|
-
|
-
|
0.5
|
3.1
|
-
|
-
|
||
Cyanophyta
|
-
|
-
|
3.2
|
6.3
|
-
|
-
|
||
Unidentified
|
1.6
|
5.6
|
4.5
|
10.9
|
3.9
|
5.3
|
||
Trophic
Level
|
2.31±0.25
|
2.88±0.36
|
3.21±0.52
|
|||||
Temporal feeding
habits of fish
Variations in feeding habits
between seasons were also observed in this study. The feeding habits of the three most
dominant species were determined over time. The feeding habits of these species were computed quarterly and were grouped into the following intervals: February/April; May/July;
August/October; and November/January.
Fish captured during
February/April, May/July and August/October had aquatic insects as the most dominant food item,
while those captured during November/January had plant material as the dominant food
item (Table 3). During the study period of February to April, three groups of feeding habits were
identified. These included insect feeders, omnivores and fish predators. Barbodes
schwanenfeldii was categorised as an insect feeder whereas Notopterus sp. was categorised as omnivorous due
to the presence of both aquatic insects and plant materials as the main feed contributor. The
only fish predator during this season was H. macrolepidota with a high trophic level value of
3.73±0.65.
During May to July, three feeding
habits were also observed. These habits were categorised as insect feeders,
omnivores and carnivores. Barbodes schwanenfeldii which fed on a high proportion of aquatic
insects (80.5%) was classified as an insect feeder. Notopterus sp. was categorised as an omnivore with a
trophic level value of 2.96±0.38, while H. macrolepidota during this season was
categorised as a carnivorous fish species.
During August to October all of
the species were categorised as omnivorous species, feeding primarily on both aquatic
insects and plant materials. Two types of feeding habits (herbivorous and omnivorous) were
categorised during the months of November to January. During this period, B.
schwanenfeldii switched their feeding strategy to be a herbivore while H. macrolepidota fed primarily on
detritus (46.2%) and thus was classified as a detritivore. In the case of Notopterussp, it
continued to remain omnivorous with a trophic level of 2.90±0.35 (Table 3).
Table 3. Temporal data
(quarterly) for the percentage composition of food items (%CFI), and frequency
of occurrence of food items (%FOFI) of three most
dominant species.
Station
|
Food
item
|
B.schwanenfeldii
|
Notopterus
sp.
|
H.
macrolepidota
|
|||||||||||
%CFI
|
%FOFI
|
%CFI
|
%FOFI
|
%CFI
|
%FOFI
|
||||||||||
February
|
Fish
|
0.1
|
1.0
|
0.6
|
2.5
|
58.3
|
33.3
|
||||||||
To
|
Aquatic
insect
|
80.1
|
31.3
|
60.4
|
17.5
|
8.3
|
13.3
|
||||||||
April
|
Molluscs
|
0.1
|
1.0
|
0.3
|
1.7
|
-
|
-
|
||||||||
Crustaceans
|
-
|
-
|
1.8
|
7.5
|
8.3
|
13.3
|
|||||||||
Plant
Materials
|
7.0
|
15.5
|
20.1
|
17.5
|
4.2
|
6.7
|
|||||||||
Detritus
|
1.5
|
1.9
|
7.1
|
15.0
|
4.2
|
6.7
|
|||||||||
Copepods
|
1.2
|
5.8
|
0.1
|
0.8
|
4.2
|
6.7
|
|||||||||
Cladocerans
|
1.2
|
5.8
|
1.5
|
5.0
|
-
|
-
|
|||||||||
Rotifer
|
1.2
|
5.8
|
1.0
|
5.0
|
-
|
-
|
|||||||||
Bacillariophyta
|
2.4
|
8.7
|
1.1
|
3.3
|
8.3
|
13.3
|
|||||||||
Chlorophyta
|
2.0
|
8.7
|
0.4
|
2.5
|
-
|
--
|
|||||||||
Euglenophyta
|
1.1
|
5.8
|
0.6
|
4.2
|
-
|
-
|
|||||||||
Cyanophyta
|
1.4
|
6.8
|
1.8
|
5.8
|
-
|
-
|
|||||||||
Unidentified
|
0.7
|
1.9
|
3.2
|
11.7
|
4.2
|
6.7
|
|||||||||
Trophic
Level
|
3.01±0.37
|
2.80±0.34
|
3.73±0.65
|
||||||||||||
May
|
Fish
|
-
|
-
|
-
|
-
|
33.3
|
42.1
|
||||||||
To
|
Aquatic
insect
|
80.5
|
27.0
|
69.8
|
22.0
|
41.6
|
26.2
|
||||||||
July
|
Molluscs
|
0.7
|
4.2
|
-
|
-
|
4.2
|
5.3
|
||||||||
Crustaceans
|
-
|
-
|
4.9
|
14.3
|
4.2
|
5.3
|
|||||||||
Plant
Materials
|
8.4
|
24.9
|
7.4
|
12.0
|
-
|
-
|
|||||||||
Detritus
|
0.4
|
2.1
|
3.4
|
11.0
|
8.3
|
10.5
|
|||||||||
Copepods
|
0.4
|
2.1
|
1.1
|
5.5
|
4.2
|
5.3
|
|||||||||
Cladocerans
|
1.8
|
6.3
|
1.8
|
3.3
|
-
|
-
|
|||||||||
Rotifer
|
1.4
|
6.3
|
1.4
|
3.3
|
-
|
-
|
|||||||||
Bacillariophyta
|
3.2
|
10.4
|
4.2
|
7.7
|
-
|
-
|
|||||||||
Chlorophyta
|
1.4
|
8.3
|
1.8
|
6.6
|
-
|
-
|
|||||||||
Euglenophyta
|
0.4
|
2.1
|
0.2
|
1.1
|
-
|
-
|
|||||||||
Cyanophyta
|
1.4
|
6.3
|
2.4
|
4.4
|
-
|
-
|
|||||||||
Unidentified
|
-
|
-
|
1.6
|
8.8
|
4.2
|
5.3
|
|||||||||
Trophic
Level
|
3.02±0.38
|
2.96±0.38
|
3.48±0.55
|
||||||||||||
August
|
Fish
|
0.6
|
1.8
|
5.0
|
7.7
|
4.9
|
15.4
|
||||||||
to
|
Aquatic
insect
|
28.7
|
9.1
|
51.8
|
11.9
|
2.5
|
7.6
|
||||||||
October
|
Molluscs
|
2.9
|
5.5
|
0.6
|
3.8
|
-
|
-
|
||||||||
Crustaceans
|
-
|
-
|
1.3
|
3.8
|
12.2
|
15.4
|
|||||||||
Plant
Materials
|
18.7
|
18.2
|
6.9
|
7.7
|
4.9
|
7.7
|
|||||||||
Detritus
|
0.6
|
1.8
|
15.0
|
15.4
|
-
|
-
|
|||||||||
Copepods
|
5.8
|
9.1
|
1.9
|
7.7
|
7.3
|
15.4
|
|||||||||
Cladocerans
|
2.9
|
7.3
|
0.6
|
3.8
|
-
|
-
|
|||||||||
Rotifer
|
4.7
|
7.3
|
2.5
|
3.8
|
-
|
-
|
|||||||||
Bacillariophyta
|
11.7
|
12.7
|
1.9
|
3.8
|
17.1
|
7.7
|
|||||||||
Chlorophyta
|
10.5
|
14.5
|
5.0
|
11.5
|
34.1
|
15.4
|
|||||||||
Euglenophyta
|
1.2
|
3.6
|
0.6
|
3.8
|
2.4
|
7.7
|
|||||||||
Cyanophyta
|
11.7
|
9.1
|
0.6
|
3.8
|
14.6
|
7.7
|
|||||||||
Unidentified
|
-
|
-
|
6.3
|
11.5
|
-
|
-
|
|||||||||
Trophic
Level
|
2.53±0.23
|
2.83±0.35
|
2.42±0.28
|
||||||||||||
November
|
Fish
|
-
|
-
|
0.9
|
2.8
|
7.1
|
7.7
|
||||||||
To
|
Aquatic
insect
|
13.3
|
15.2
|
69.3
|
24.7
|
7.2
|
7.6
|
||||||||
January
|
Molluscs
|
13.8
|
6.1
|
-
|
-
|
-
|
-
|
||||||||
Crustaceans
|
-
|
-
|
0.6
|
2.8
|
-
|
-
|
|||||||||
Plant
Materials
|
53.9
|
28.8
|
11.2
|
18.1
|
35.7
|
30.8
|
|||||||||
Detritus
|
6.4
|
19.7
|
8.8
|
16.7
|
42.9
|
46.2
|
|||||||||
Copepods
|
5.0
|
9.1
|
0.9
|
4.2
|
-
|
-
|
|||||||||
Cladocerans
|
0.4
|
1.5
|
1.9
|
1.4
|
-
|
-
|
|||||||||
Rotifer
|
0.7
|
1.5
|
0.4
|
2.8
|
-
|
-
|
|||||||||
Bacillariophyta
|
0.7
|
3.0
|
0.6
|
2.8
|
-
|
-
|
|||||||||
Chlorophyta
|
3.9
|
7.6
|
1.7
|
5.6
|
7.1
|
7.7
|
|||||||||
Euglenophyta
|
0.4
|
1.5
|
0.7
|
4.2
|
-
|
-
|
|||||||||
Cyanophyta
|
0.4
|
1.5
|
0.4
|
1.4
|
-
|
-
|
|||||||||
Unidentified
|
1.1
|
4.5
|
2.6
|
12.5
|
-
|
-
|
|||||||||
Trophic
Level
|
2.39±0.21
|
2.90±0.35
|
2.26±0.24
|
||||||||||||
Discussion
The variations in trophic level
values among the six species of fish examined in this study suggested that these fish have
different feeding requirements and strategies. In general, two of them were found to be specialist
feeders and four of them were found to be generalist feeders. The four species which were
generalists were categorised as primary consumers and were classified as omnivorous species,
while the other two species which were categorised as secondary consumers were
classified as predators. Although the lake is considered oligotrophic with low productivity (Yusoff et
al. 1995), most fish in the studied lake section showed a high food intake.
Hemibagrus
nemurus exhibited
a feeding trend dominated by the main diet item of aquatic insects. Aquatic insects
as a food item were also important in the diets of three other species although they were
categorised as omnivorous species. Aquatic insects which were found in fish stomachs may have been
due to the location of the lake which is situated within the primary rain forest on the hilltops of the state of
Terengganu. Insects are very common in Kenyir Lake (Hasan and Ambak, 2005).
According to Rouf et al. (2008), the Kenyir Lake catchment area was originally part of the
dense, hilly forest which provided for the abundance of insects.
The abundance of insects in fish
stomachs were also reported by Sakri et al. (2010) in their study in Kenyir Lake. Their
study listed the groups of insect species and this included mayflies, fireflies, water
beetles, water striders and dragonflies. According to Mason and MacDonald (1982), the abundance
of this fish group is related to the easy capture of insects in aquatic ecosystems. Furthermore,
insects are rich in proteins and nutrients (Nico and Morales, 1994).
The use of ‘food items of animal
origin’ such as aquatic insects and fish prey food items in the diet of omnivorous species
was almost consistent with the intake of ‘food items of plant origin’ such as plant material
and phytoplankton. It is possible that this kind of group is more of a generalist, using other types
of food when they are available in larger amounts (Melo et al.2004). According to
Lowe-McConnell (1987) generalist species have a better chance to become widely distributed in an aquatic
ecosystem. This could be the reason for the dominance of omnivorous species such as B.
schwanenfeldii, Notopterus sp. and H. macrolepidota in this
lake section.
On the other hand, only one
piscivorous (C. micropeltes) species was observed during the duration of this study. The
stomach contents of C. micropeltes were found to contain the highest percentage of fish food items.
This was almost similar to the results of the study by Sakri et al. (2010) who studied the stomach
contents of fish species in Kenyir Lake and classified this species as a piscivore. The
morpohometric characteristics of C. micropeltes clearly showed that this species was a real predator.
Channa micropeltes was piscivorous with a strong jaw and wide mouth aperture (Wootton, 1998).
Although the intake of fish food prey item provides high quality nutrients, the feeding
strategy of predators required complex adaptations to overcome the defence strategies of their prey
(Keenleyside, 1979).
Different trends of feeding
habits were observed seasonally and spatially. Sungai Ikan is actually a good site where the
simplest feeding habit is exhibited because all of the three dominant species (B.
schwanenfeldii, Notopterus sp. and H. macrolepidota) were
categorised as omnivores. None of them was
classified as aquatic insect feeders although B. schwanenfeldii and Notopterus sp. fed on this
prey. The most complex feeding habits were observed at Pulau Pupi. Some fish species earlier known
as omnivores changed their diet to include plant materials and became herbivorous, or include
fish food items and became a carnivorous species. This could be a consequence of a wider variety
of food items available in this habitat for fish species to select (Hajisamae et al. 2003).
Temporally, some fish species underwent changes in their feeding habits during different seasons. These
were B. schwanenfeldii and H. macrolepidota. They shifted from aquatic
insect feeders to herbivores for B. schwanenfeldii, and from piscivorous
species to detritivore for H.
macrolepidota. On the other hand, carnivorous species were present during February/April and May/July.
However, this carnivorous guild was absent during August/October and
November/January. According to Hajisamae et al. (2003), the dietary shifts are probably a major feature in
structuring the trophic guild in the habitat.
Although H. macrolepidota had
fish food prey items in its diet during November/January, this was accompanied by other
food items such as detritus. Thus this species was considered as detritivorous species. The types
of detritus found were fish scale, rock, sand and mud. From this finding, it is evident that the
detritivory habit may be one of the important feeding strategies available during this season.
Caragitsou and Papaconstantinou (1994) described that the organic content of mud may play an
important role in the nutrition of fishes. This is because detritus contains large amounts of
microorganisms (Keenleyside, 1979).
The feeding patterns during
February/April and May/July could be categorised into three different feeding guilds observed
in each season. This indicated that the three species fed on specific types of food items due
to abundance and availability of each food item during each season. However, the specific
types of feeding guilds need not necessarily mean that the species feeds completely on a different
suite of food. There was some overlap in food choices where aquatic insects, plant materials
and zooplankton were found in all the stomachs of these fishes. The fish species in each particular
habitat, however, has many strategies for avoiding trophic competition and for optimising available resources
(Hajisamae et al. 2003).
Conclusion
Stomach contents of the six fish
species can be used as indicator of their diet. The differing stomach contents
consisted of a variety of food items. The food items varied from the smallest organisms such as
phytoplankton and zooplankton to the biggest prey such as fish, molluscs and crustaceans. This
indicated that these different fishes depend on one another and also depend on the stability of
the ecosystem which provided the suitable food sources for the fish. The findings of this study
are expected to be valuable inputs for the planning and management strategies towards the
sustainability and conservation of the fisheries resources. Future studies can be conducted
to better understand the fish population in Kenyir Lake. The
Pengkalan Gawi–Pulau Dula section
of Kenyir Lake can be properly managed and developed for eco-tourism and fish production
on a sustainable basis.
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