Feeding Guild of the Dominant Trawl Species in the Southeastern Waters of Peninsular Malaysia
In this study, stomach content analyses were used to determine the feeding guild of dominant trawl species comprising leiognathids and priacanthids. Specimens were collected from the southeastern coastal waters of Peninsular Malaysia using commercial trawler. Five species of leiognathids and two species of priacanthids were caught throughout the study. The results showed that the mean value of trophic level for leiognathid species, Photopectoralis bindus was 3.22±0.49, Gazza minuta was 2.75±0.29, Secutor indicius was 2.87±0.30, Eubleekeria jonesi was 2.49±0.27, Equulites stercorarius was 2.63±0.30 and for priacanthid species, Priacanthus macracanthus was 3.51±0.47 and Priacanthus tayenus was 3.61±0.45. The results indicated that the feeding regime of P. bindus, G. minuta and S. indicius can be categorized as bentho-pelagic feeders that have forwardly or upwardly protractible mouth types and feed mainly on zooplankton and zoobenthos. E. stercorarius and E. jonesi with a downwardly protractible mouth type feed mainly on zoobenthos and can be classified as benthivorous. The results suggested that the forwardly or upwardly protractible mouth types leiognathids occupy a higher trophic level compared to the downwardly protractible mouth type leiognathids. Both priacanthids with upturned mouth type have similar diet composition consisting of crustaceans, polychaetes, ostracods, fish and cephalopods. They are thus mid-level carnivores since the species are able to consume organisms at trophic level 3.5. The results revealed that the value of trophic level for priacanthid species were higher than leiognathid species.
Received: February 10, 2011;
Accepted: May 19, 2011;
Published: June 25, 2011
Trawling is probably one of the most important marine fishing techniques and
it dominates the Malaysian fishery industries economically. It has a major impact
on society and the countrys economic development (Musa
and Nuruddin, 2005). However, it has always been the most controversial
fishing method throughout the world since it involves dragging huge and heavy
nets along the sea floor (Gillett, 2008). Trawling has
contributed a significant portion to the catch of untargeted fish, known as
by catch which is considered as low value fishes (Davies
et al., 2009). However, the development of the surimi industry in
Malaysia has increased the value of the by catch and provided market profitability.
Thus the by catch now could be an important income for trawlers (Pangsorn
et al., 2007) and help reduce wastage from trawling. Threadfin bream,
lizard fish, bigeye fish, croaker and goatfish are economically important by
catch species as surimi raw materials (Pangsorn et al.,
Priacanthids and leiognathids were the dominant by catch fishes in this current
study. Priacanthids (family Priacanthidae) commonly known as bigeyes, are widely
distributed in the coastal water of tropical and subtropical Atlantic, Indian
and Pacific oceans. This fish species is generally recognized by its extremely
large eyes and upturned mouth. They are a kind of epibenthic fishes usually
available in coral reefs and rock formations, although they occasionally venture
in more open areas at depths of 5 to 400 m. They occur solitarily or in small
aggregations but some species may form large mixed feeding schools of a few
to several species. Eggs, larvae and early juvenile stage are pelagic. Most
members of priacanthids are nonguarders (Starnes, 1984,
1988). Priacanthids are commercially important by-catch
fishes in Malaysian fisheries used as common commercial food fish. Several analyses
of these fishes have been carried out focusing on taxonomy and distribution
(Starnes, 1988), age and growth (Liu
et al., 1999), food chemistry and hydrocolloids on Priacanthids
skin (Jongjareonrak et al., 2006).
Leiognathids (family Leiognathidae) commonly known as ponyfishes, are widely
distributed in the coastal waters of sub-tropical and tropical regions (Woodland
et al., 2001). In Malaysia, it is known as kekek, a moniker based
on the chirping sound the fish makes. These fishes commonly inhabit turbid coastal
waters of poor visibility such as shallow coastal waters, mangrove areas and
estuaries (Sparks et al., 2005), although they
occasionally venture into freshwater reaches of rivers. They are demersal fishes
that usually form large mixed feeding schools of a few to several species on
the shallow water sea floor. In some parts of Malaysia, leiognathids are sold
freshly or processed into popular fish crackers and salty dried fish showed
this fish have commercially important (Mazlan and Seah, 2006).
Generally by catch species has received less attention in icthyological research. Detailed accounts on the feeding regime and trophodynamic analyses of by catch species are still lacking. Feeding guild information is used to assess the trophodynamic levels of fishes in their natural environment and revealed the existing organisms at the area. Preliminary study of both fishes is in need to investigate the existing species in Malaysian waters and it will enhance the further study for these particular families. The present study is an was aimed to examine the diet composition and trophic levels of dominant trawl species present in the southeastern waters of Peninsular Malaysia.
MATERIALS AND METHODS
A series of trawl surveys were conducted in southeastern Peninsular Malaysia
coastal waters. A total of 12 hauls were made throughout the study during August
2008 which covered trawled areas off Tioman Islands within N02° 54.799:
E104° 06.163-N02° 54.310: E104° 08.130, N02°
50.263: E104° 09.024-N02° 48.334: E104° 08.041
and Sibu-Tinggi Islands N02° 15.679: E104° 00.290-N02° 17.454:
E103° 54.471, N02° 13.725: E104° 01.253-N02°
13.105: E104° 00.508. An otter trawl net was deployed throughout
the study to catch fishes at depths ranging from 15 to 25 m. The trawl was equipped
with a 1 ¼ inches mesh size cod end. Each trawl lasted about 3 h at a
towing speed of 2.0-3.0 knots. The dominant trawl species caught were leiognathids
and priacanthids. All catches were sorted in accordance to the standard protocol
listed by Sparre and Venema (1998). Fresh sub-samples were
kept on ice prior to further biological investigation at the field-laboratory
station. Voucher specimens of fishes were photographed for their whole body
and some detailed morphological characters such as extension of mouth and fins.
All sub-samples collected were then fixed in 10% formalin during the field study
and later transferred into 70% alcohol prior to the further study.
Species identification was made in accordance to the standard studies (James,
1984; Masuda et al., 1984; Starnes,
1984; Mohsin and Ambak, 1996; Mansor
et al., 1998; Woodland et al., 2001;
Nakabo, 2002; Kimura and Matsuura, 2003).
In order to minimize the rigor mortis process of the gut content, gut sacs (stomach
and intestine) were extracted from each species soon after identification. The
guts were pre-fix in 10% formalin and later, the contents were completely emptied
into labeled Petri dishes containing 70% alcohol. The labeled dishes were sealed
using high-density cellophane tape and packed into a box. In the laboratory,
the gut contents were sorted and observed under a dissecting microscope to record
the types of food materials present (Jimmy et al.,
2003). The stomach content was classified and the trophic level was calculated
using TrophLab® software (Pauly et al., 2002).
Leiognathids and priacanthids were the dominant trawl species in this study.
Five species of leiognathids namely Photopectoralis bindus, Gazza
minuta, Secutor indicius, Eubleekeria jonesi and Equulites
stercorarius and two species of priacanthids, Priacanthus macracanthus
and Priacanthus tayenus were identified. The results showed that the
mean value of trophic level for P. bindus was 3.22±0.49,
G. minuta was 2.75±0.29, S. indicius was 2.87±0.30,
E. jonesi was 2.49±0.27 and E. stercorarius was 2.63±0.30
(Fig. 1). Priacanthids have almost similar mean value of trophic
level, P. macracanthus was 3.51±0.47 and P. tayenus was
3.61±0.45 (Fig. 2). Each species has demonstrable differences
in diet composition and food consumption except for the priacanthid species
which have similarity of food items (Fig. 3).
|| Trophic level of leiognathid species
|| Trophic level of (a) Priacanthus macracanthus and
(b) Priacanthus tayenus
|| The occurrence of food items in the diet of dominant trawl
The percentage of detritus found in leiognathids was greater than in priacanthids.
Polychaeta was the only food item found in every fish species stomach.
Priacanthids consumed mainly crustaceans and polychaetes but also ate a small
portion of finfish, ostracods and cephalopods. P. bindus, G. minuta
and S. indicius have almost similar food items. They were fish larvae,
copepods, polychaetes and euphausiids, whereas prawn was found in P. bindus
and amphipods were found in S. indicius. E. stercorarius and E.
jonesi have high amount of detritus in their diet compared to other leiognathid
species. They have quite similar food items except for the occurrence of euphausiid
in the diet of E. stercorarius and non-annelida in the stomach of E.
The trophodynamic analysis values as indicated in the results showed that the
leiognathid and priacanthid populations in the study areas consumed mostly benthic
organisms. The calculated trophic level values ranged between 2.4-3.5 for leiognathids
and 3.0-4.5 for priacanthids, respectively. The trophic level values of leiognathids
fell between omnivorous and mid-level carnivorous according to TrophLab scales,
indicating different categories of feeding regimes in leiognathids in comparison
to other groups of fish species. These were due to the nature and morphology
of the feeding instrument (protractible mouth and teething system) in leiognathids
that is particularly well-suited for picking benthic organisms such as polychaetes
and copepods in the sediment (Mazlan and Seah, 2006).
P. bindus, G. minuta and S. indicius have forwardly or
upwardly protractible mouth types and feed on zooplankton and zoobenthos and
thus can be categorized as bentho-pelagic feeders. E. stercorarius and
E. jonesi with a downwardly protractible mouth type and villiform teeth
feed mainly on zoobenthos and can be classified as benthivorous. The results
suggested that the forwardly or upwardly protractible mouth types of leiognathids
suit a higher trophic level compared to the downwardly protractible mouth type
of leiognathids. This feeding regime defines the leiognathids' feeding habit
as neither omnivorous nor mid-level carnivorous but instead can be categorized
as benthivorous or bentho-pelagic feeder according to genus as they usually
move around in large schools on the sea bottom while nibbling the sediments
in search of benthic organisms. The trophic level values of priacanthids fell
between mid-level carnivorous and high-level carnivorous. Priacanthids have
an upturned mouth type and conical teeth, providing the ability to hunt nekton
but consumed mainly zoobenthos. The feeding regime defines the priacanthids'
feeding habit as mid-level carnivorous as they usually consumed mainly benthic
organisms. The results showed that priacanthids occupy a higher trophic level
compare to leiognathids.
The variations of food items of the leiognathid species found in this study
are almost similar to the results reported by James (1984).
However, the trophic level values reported by Froese and Pauly
(2008) were different from the current study. The trophic level values for
Gazza and Secutor was more than 3.4, P. bindus was 2.5
and other leiognathid species was 2.8 and above. The abundance of detritus in
the stomach content of leiognathids at between 30-60% was the major factor affecting
the trophic level values. If the field extracted stomach was not properly preserved,
the food items would mix with denaturing enzymes and hydrochloric acid fluids
in the stomach, fostering rigor-mortis decomposition processes that convert
the solid food item into chyme. This will contribute to a common error in assessing
food composition prior to trophodynamic analysis (Mazlan
and Grove, 2004). However, a properly conducted study will provide promising
results in estimating trophodynamics of organisms in their natural environment.
Such analysis also provides clues on how the marine habitat can sustain biological
functions of organisms living in it (Bray et al.,
1981; Hobson, 1991). Crustacean was the primary food
item consumed by both priacanthid species as reported by Mansor
et al. (1998). Ibrahim et al. (2003)
reported that 79% of the diet of P. tayenus comprised of crustaceans
but it was only 44% in the present study. The trophic level values of P.
tayenus was almost similar to Salini et al. (1994),
3.7 and Yamashita et al. (1987), 3.9.
The present study has revealed the feeding dynamics of the leiognathid and priacanthid fish species in the coastal waters of southeastern Peninsular Malaysia. The muddy seabed surrounding the study areas can apparently support several important genera of infauna invertebrate species such as polychaeta, crustacean and other co-existing invertebrate species found in the feeding guilds of leiognathid and priacanthid fish species.
This study was supported by the Universiti Kebangsaan Malaysia Research University Grant Scheme (UKM-MI-OUP-2011, UKM-GUP-ASPL-08-04-235, UKM-04-01-02-SF0124, UKM-OUP-FST-2010) and the Malaysia government (MOSTI, NSF L6438). The authors would like to thank the laboratory assistants of Universiti Kebangsaan Malaysia for technical assistance.
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