Oxyeleotris marmoratus, Predator or By-Product in Integrated Aquaculture Ponds
Participating farms in the Muang district of Nong Khai
Province, were selected for the investigation of management practices
and yields of marble goby, Oxyeleotris marmoratus, in integrated
culture with Nile tilapia (Oreochromis niloticus). The research
took place from February to May, 2007. The observed production of O.
marmoratus in integrated aquaculture ponds indicated a wide range
of management practices. The yields of Oxyeleotris marmoratus were
between 22.1 to 316 kg ha-1 (average 81 ±78 kg ha-1).
The farmers tended to prefer Oxyeleotris marmoratus not only as
a by-product, but also as the main product from their ponds. Most farmers
realized that Oxyeleotris marmoratus predate Nile tilapia fingerlings
from the natural spawning of mature Nile tilapia in the ponds. With respect
to consumed prey, the frequency of occurrence of prawns was 73.3%, whilst
that of small fish was 43.3%. In terms of prey biomass, prawns were also
the most abundant food item, giving the relative abundance of 56.0%. A
preliminary trial on predation pressure was conducted to confirm the role
of Nile tilapia fingerling as live feed for Oxyeleotris marmoratus
in integrated aquaculture ponds and it was found that the daily predation
pressure was between 1.90 to 2.46 fish day-1.
In natural conditions, Oxyeleotris marmoratus is
found in rivers, swamps, reservoirs and canals along the Mekong and Chao
Phraya river basins and also in the Malay Peninsula, Indonesia and the
Philippines (Kottelat et al., 1993). This demersal fish feeds mainly
on macrofauna such as prawns, benthos, small fish, crabs and aquatic insects,
with a trophic level from 2.8 to 4.05 (Yap, 1988;Roberts, 1993). It may
be the largest species of goby-like fishes, attaining a maximum standard
length of 65 cm (Kottelat, 2001). Oxyeleotris marmoratus is a high-valued
species (US$4 to 12 per kg) and has been cultured within cages in reservoirs,
lakes and ponds in several Southeast Asian countries such as Malaysia,
Thailand and Vietnam. Cage culture of Oxyeleotris marmoratus often
suffers from serious disease problems caused by Aeromonas hydrophilla.
As an example, the production of Oxyeleotris marmoratus reduced
drastically in Thailand during the 1990s, resulting mainly from outbreaks
of disease (Lin and Kaewpaitoon, 2000). Other problems in the culture
of Oxyeleotris marmoratus include the lack of formulated feeds
(Jee, 1980; Cheah et al., 1994; Lin and Kaewpaitoon, 2000).
Oxyeleotris marmoratus is one of the most important
freshwater fish in commercial aquaculture as its tender, non-bony flesh
and taste has led to an increasing market demand. The farming of Oxyeleotris
marmoratus in Thailand is expanding but the production is limited.
The small scale farmer sells live Oxyeleotris marmoratus for as
high as US$8.8 per kg (Ingthamjitr et al., 2005) which is the highest
price among freshwater fish in Thailand. Striped Snakehead (Channa
striata) and Oxyeleotris marmoratus are the main carnivorous
species cultured in northeastern Thailand. Recent figures show the annual
aquaculture production of these fish was 540 and 0.7 metric tons respectively
(DOF, 2004). In a typical case of small-scale cage culture of Oxyeleotris
marmoratus on the Songkhram River in Nakhon Phanom Province, the fish
farmer had two small 3x6x3 m cages: each cage was stocked with 300 wild
juveniles that had been collected by the farmer, each fish weighing between
100 to 200 g. The caged fish were fed fresh fish collected from the river
once a day and as a supplement, pellet feed and apple snail flesh were
also used. The quantity of feed increased from 2 kg day-1 in
the first month to approximately 7 kg day-1 in the month preceding
harvesting (Ingthamjitr et al., 2005).
To maximize fish production utilizing the available food
organisms in ponds, the polyculture of many varieties of fish with different
feeding niches has been commonly practiced (Olah, 1980). Feed cost is
considered to be the highest recurrent cost in aquaculture, often ranging
from 30 to 60%, depending on the intensity of the operation (De Silva
and Anderson, 1995). The use of animal manures for fish culture is an
extension of traditional land-crop cultivation, which uses available on-farm
resources within the reach of many small-scale farms in Asia (Zhu et
al., 1990). The concept of tilapia production based on waste as feed
for high market value carnivorous fish was proposed by Edwards (1988).
To control overcrowding and its associated effects, culture with predators
has also been studied: Channa striata or Ophiocephalus striatus
(Chimits, 1957; Tongsanga, 1962; Chen, 1976; Cruz and Shehadeh, 1980;
Hopkins et al., 1982; Wee, 1982); Ophiocephalus obscures
(de Graaf et al., 1996); Micropterus salmoides (Swingle,
1960; Meschkat, 1967; McGinty, 1985); Lates niloticus (Meschkat,
1967;Bedawi, 1985;Ofori, 1988;El Gamal, 1992); Hemichromis fasciatus
(Bardach et al., 1972); Clarias sp. (de Graaf et al.,
1996); Cichlasoma managuense (Dunseth and Bayne, 1978); Elops
hawaiiensis (Fortes, 1980) and Megalops cyprinoides (Fortes,
Cannibalism is the act of killing and consuming the whole
or major part, of an individual belonging to the same species, irrespective
of its stage of development. It is a common and widespread phenomenon
throughout the animal kingdom. In fishes, cannibalism occurs at various
sizes or ages and extends within and between cohorts or age classes, depending
on species and environmental conditions (Smith and Reay, 1991). It is
usually associated with size variation, limited food availability, high
population densities, limited refuge areas and light conditions (Hecht
and Pienaar, 1993). When looking at the size of prey, both the size of
the predator`s pharyngeal gape and oral gape are obvious restricting factors.
Lawrence (1957) suggested that the pharyngeal gapes in Largemouth Bass
and Bluegill are significantly smaller than their oral gapes and Sibbing
(1991) stated that the presence of pharyngeal jaws and the palatal organ,
narrowing the pharyngeal slits, seems more likely to restrict prey size
among piscivorous Barbus rather than the oral gape. Many laboratory
studies show that fish eat prey as wide as their mouth diameter, even
if the pharyngeal gape is actually narrower than size of the prey (Kisalioglu
and Gibson, 1976). This is due to the fact that most prey are deformable;
once the fish prey is captured by the predator it can be swallowed, even
if it is wider than the pharyngeal gape, as its shape can be altered by
the actions of the pharyngeal jaw apparatus as the prey is being swallowed.
Pharyngeal gape is likely to be more significantly constrained when the
prey has a rigid, inflexible exoskeleton or shell (Wainwright and Richard,
From an aquaculture point of view, carnivorous fish (Channa
striata and Clarias catfish) in aquaculture ponds are predators,
but some researchers mention their role as a high market value by-product,
especially the C. striata. Small scale aquaculture faces a problem
of over crowding by Nile tilapia spawning which leads to low production
levels of marketable size fish. Sex-reversal male Nile tilapia is not
effective in long term pond culture and the control of predator fish is
not effective in most pond fish culture on small scale farms (either the
ponds are undrainable or cannot be completely drained). Thus, as a new
approach in producing high market value fish, the integration of the culture
of the predator, Oxyeleotris marmoratus, with Nile tilapia is a
challenge in terms of pond aquaculture, especially under small scale operations.
This study describes the present practices of small-scale
farmers in this area relating to the production of carnivorous fish,
Oxyeleotris marmoratus, by utilizing integrated aquaculture concepts.
It includes a preliminary laboratory trial on the predation pressure of
Oxyeleotris marmoratus on Nile tilapia fingerlings to confirm that
Nile tilapia fingerlings can be a source of live feed for the O. marmoratus.
MATERIALS AND METHODS
Study area and production layout: Nong Khai Province is the northernmost
of the northeastern provinces of Thailand, located in Mekong River Basin,
which also forms the border with Laos. The province is subdivided into
13 districts (Amphoe) and 4 minor districts (King Amphoe). Participating
farms in Muang district, Nong Khai, were selected for an investigation
into pond environment conditions and the production of Oxyeleotris
marmoratus in integrated culture with Nile tilapia. The research took
place from February to May, 2007. Integrated water samples were taken
from the entire water column near the center of each pond at about 09:00
to 10:00 h for water analysis. The chemical parameters of the pond water
(total alkalinity (mg CaCO3 L-1), total hardness
(mg CaCO3 L-1) and chlorophyll a concentrations
(µg L-1)) were analyzed according to standard methods (APHA,
1985). At the time of collecting the water samples, the visibility (cm)
was measured using a Secchi disc, temperature (°C) and conductivity (µS
cm-1) by a Hach model Sension 5, dissolved oxygen (mg L-1)
by a YSI model 52 oxygen meter and the pH level with a Consort C533 meter.
Gut content: Oxyeleotris marmoratus (200 to 300
g) were randomly sampled from 20 fish ponds in the study area for gut
content analysis, with the samples being fixed immediately upon capture
with a 10% formalin solution. The formalin solution was also injected
directly into the fish coelom and gut to avoid post-capture digestion.
Quantitative analysis of gut content was described by two parameters:
frequency of occurrence (Ofi) and the relative abundance of
prey in terms of weight (Awi), which was calculated using the
following formula (Bowen, 1996; Jobling et al., 2001):
||No. of fish with prey i in the stomach
||No. of stomachs with food
||Weight of prey i in the stomach
||Total weight of stomach content
Predation pressure of Oxyeleotris marmoratus on Nile tilapia
fingerling: Over 30 days the predation of Oxyeleotris marmoratus
on Nile tilapia fingerlings was observed in triplicates of different containers;
glass aquariums (75 L of water), circular fiber tanks (150 and 300 L of
water). All the containers were aerated with an air diffuser during the
trial. A single Oxyeleotris marmoratus (200 to 300 g) was added
to each container and fed with two different prey densities; 15 and 30
prey per container. The prey, Nile tilapia fingerlings, was categorized
into three size groups: small (S), 0.5 to 2.0 g; medium (M), 2.0 to 5.0
g and large (L), 5.0 to 10.0 g. Five and ten tilapias of each size group
were mixed at a 1:1:1 ratio according to prey density. The numbers and
sizes of the prey consumed daily were determined by noting the difference
between the initial prey stock and that remaining after 24 h. Any dead
or consumed fish were then replaced with fish of a similar size. With
respect to the chemical parameters of the ground water used in the containers,
the total alkalinity (mg CaCO3 L-1) and total hardness
(mg CaCO3 L-1) were analyzed according to standard
methods (APHA, 1985). The temperature (°C) and conductivity (µS cm-1)
were measured by a Hach model Sension 5, dissolved oxygen (mg L-1)
by a YSI model 52 oxygen meter and the pH level with a Consort C533 meter.
The daily predation pressure was determined using the following formula
RESULTS AND DISCUSSION
The observed production of Oxyeleotris marmoratus
in integrated aquaculture ponds indicated a very wide range of practices
and yield. From the 20 ponds observed it was found that for those covering
an area between 0.32 to 5.70 ha (average 1.27±1.28 ha), the stocking density
of Nile tilapia was between 0.12 to 16 fish m-2 (average 3.1±4.7
fish m-2) and the yield of Oxyeleotris marmoratus between
22.1 to 316 kg ha-1 (average 81±78 kg ha-1). There
were only 10 farms in this study that had been intentionally stocked with
Oxyeleotris marmoratus from hatcheries or other ponds. The remaining
farms had acquired wild Oxyeleotris marmoratus stock through flooding
during the rainy season or from irrigated water from rivers or reservoirs.
It was also found that these ponds had not been drained properly prior
to their use. The farmers tended to prefer Oxyeleotris marmoratus
not only as a by-product but also as a main product from their ponds,
due to the fact that its market value was 10 times higher than that of
Nile tilapia and carps. The farm gate price for Oxyeleotris marmoratus
with a body weight of more than 400 g was about US$10 per kg. The marketing
of the fish was uncomplicated for the farmers, as merchants came direct
to the farms to purchase them.
Another reason why Oxyeleotris marmoratus was a preferred
product was the lack of necessity in feeding them, as most farmers realized
that O. marmoratus predate the fingerlings from the natural spawning
of the mature Nile tilapia in the ponds. There were, however, some farmers
who bought more Nile tilapia fingerlings from hatcheries as feed for the
Oxyeleotris marmoratus. This possibly indicates that those farmers
had some misunderstanding regarding relevant ecology. Tilapia are an excellent
culture species, partly because they grow well on a variety of natural
food organisms, including plankton, green leaves, benthic organisms, aquatic
invertebrates, larval fish, detritus and decomposing organic matter (Schroeder,
1978). The stocking of predatory fish, such as the Channa strita,
in small numbers may control excessive reproduction and hence maintain
a balanced pond population; the potential for fry control exists in many
species (Little and Muir, 1987). Little et al. (1996) mentioned
that the most valuable role the fry or fingerlings of tilapias produced
in rice fields may be as a food source for wild fish. Middendorp (1992)
indicated that yields of unstocked wild fish were less variable and on
average, much higher when tilapias were stocked (325 vs. 163 kg ha-1).
However, when compared to the Channa strita, the market price of
Oxyeleotris marmoratus is much higher (4 times). The yield of Oxyeleotris
marmoratus from integrated aquaculture ponds in the present may not
reflect the carrying capacity of those ponds because the appropriate stocking
density of the O. marmoratus integrated with Nile tilapia culture
has not been studied. The major constraint is the lack of Oxyeleotris
marmoratus seed in the area; most are wild seed that directly entered
the fish ponds from external water supplies, although some farmers do
buy the small size Oxyeleotris marmoratus (<200 g) from the small-scale
The harvesting of the Oxyeleotris marmoratus is easily
done by trapping, which is not as labor intensive when compared to seining
and the smaller sized ones (<200 g) are often restocked back into the
pond or other ponds. On the other hand, the use of trapping in the partial
harvesting of Channa strita from integrated culture or polyculture
systems is more difficult and not as efficient.
In general, most integrated aquaculture ponds that receive
high organic matter loading tend to have adverse effects on the fish;
however, the Oxyeleotris marmoratus is a facultative air-breather
fish capable of surviving under terrestrial conditions for up to a week
Oxyeleotris marmoratus appears to be the first known teleost that
responds to air exposure by activating hepatic glutamine synthetase to
detoxify internally produced ammonia (Jow et al., 1999). In the
present study the level of basic water quality parameters, visibility
and chlorophyll a concentrations indicated a eutrophic condition in the
fish ponds (Table 1) and the effect of water quality
on the yield of Oxyeleotris marmoratus needs to be verified further.
Gut content analysis of Oxyeleotris marmoratus from
fish farms showed that the frequency of occurrence of prawns was 73.3%,
whilst that of small fish was 43.3%. In terms of prey biomass, prawns
were also the most abundant food item, giving the relative abundance of
56.0% (Table 2). The size of tilapia fingerlings ranged
from 0.09 to 6.09 g and 1.7 to 5.5 cm and the prawns from 0.02 to 0.48
g and 1.0 to 4.2 cm. A study on the cove culture of Oxyeleotris marmoratus
and carps in the Tri An Reservoir in Vietnam showed that the major food
items of O. marmoratus were small fresh water prawns, followed
by small wild fish and benthos (Luong et al., 2005). In the case
of aquaculture ponds, freshwater prawns and benthos may be consumed by
other fish. However, the results confirmed that yield of Oxyeleotris
marmoratus is dependant, or partly dependant, on Nile tilapia and
that Nile tilapia is a major food source of O. marmoratus in this
The preliminary trial on predation pressure was conducted to confirm
the role of Nile tilapia fingerlings as live feed for Oxyeleotris marmoratus
in integrated aquaculture systems. The results of the experimental
Summarization of water quality
of water sampled at 0900-1000 am from 20 fish ponds in Nong
Khai province during February to May 2007
||Gut content of Oxyeleotris marmoratus sampled
from selected farms from February to May 2007
Ni = No. of stomach
with food, Nf = No. of fish with the prey i in the
stomach, Si = Weight of prey i in stomach content,
St = Total weight of stomach content
||Summarized data of predation pressure trial of marble
goby (Oxyeleotris marmoratus) on various sizes of Nile
tilapia fingerling (prey) at 15 and 30 preys/container
units water analysis showed that the total alkalinity (mg
CaCO3 L-1), total hardness (mg CaCO3
L-1), temperature (°C), conductivity (µS cm-1),
dissolved oxygen (mg L-1) and pH were 305±2.3, 194±7, 26.2±0.15,
360±22.5, 6.2±0.4 and 9±0.1, respectively. The daily predation pressure
was between 1.9 to 2.46 fish per day (Table 3). Size
variation is considered one of the primary causes of cannibalism (Hecht
and Appelbaum, 1988; Katavic et al., 1989) and the notion that
the gape of the predator is an important constraint on prey use is wide
spread in fish biology and is frequently cited as the explanation for
correlations between prey and predator body size (Shirota, 1978; Felley,
1984). It has been stated that the Channa strita could consume
prey bigger than the size predicted from the predators` mouth width (Qin
and Fast, 1996), so further study should be undertaken to verify the prey
size selection of Oxyeleotris marmoratus.
Oxyeleotris marmoratus is not a by-product, but rather
acts as a cash crop in integrated culture with Nile tilapia in the study
area. An improvement in the present culture practice of Oxyeleotris
marmoratus may lead to increased yields and higher incomes for the
rural farmers who face problems with regards to the use of commercial
feed. This culture system may reveal ecological aquaculture concepts for
the production of carnivorous fishes.
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