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(Photo under Creative Commons Attribution-Share Alike 3.0 Unported, 2.5 Generic and 1.0 Generic license: Djatmiko, W. A.)
Table of Contents
Potential threats on the environment
You might have heard of Soon Hock, or might have even tasted it before. The common Soon Hock is more widely used in Singapore. The scientific name of Soon Hock is
, and it is a rather expensive delicacy in Singapore as well as in many other Asian countries [
]. Apart from catching them from the wild, Soon Hock can also be reared. The understanding of their biology, such as the living environment and feeding habits, might allow more effective management of Soon Hock farms. It might also be interesting to see how Soon Hock can be suitable for aquaponics, which might be a potential form of sustainable food production [
Soon Hock can be found in freshwater and brackish water [
]. Example of such environments are rivers, swamps, reservoirs and canals [
]. They only migrate within freshwater [
] and prefer non-moving water with dense aqua flora [
]. Juveniles are found in moving streams with substrates such as rocks and sand [
]. Soon Hock can also survive without water for a few days [
]. It was also observed that they air breathe by holding air in their mouths [
]. Soon Hock of average size of 81 g can live well in water with 4.5 to 7.8 ppm dissolved oxygen, a pH range of 6.6 to 7.3 and a temperature range of 27 to 31.4 degree Celsius [
]. However, there is no published Information on the tolerance limits of Soon Hock [
Soon Hock is carnivorous and feeds on various other organisms such as small fish, molluscs, crabs, shrimps and aquatic insects [
]. In nature, they are usually motionless and ambush their prey [
]. Their cryptic colour allows them to camouflage (Figure 1) and stay unnoticeable to their preys. Although artificial feed might be preferred to live feed when rearing fish because of factors such as cost and food safety [
], fingerlings of Soon Hock have higher survival rates when fed with live feed compared to artificial feed [
]. However, artificial feed for fingerlings of many carnivorous fish has not been well developed yet [
] and it is only until recently that artificial feed is used in Soon Hock cultivation [
]. There are studies on more suitable artificial feeds for Soon Hock fingerlings [
] and more could be done in future.
Video 1. Marble goby weaned on artificial feed
Figure 1. Well camouflaged 20 cm specimen found in a shallow stream in Singapore. (Photo: Nick Baker, permission obtained)
Figure 2. Soon Hock fingerling (Source: Nhi et al., 2010; permission granted)
The feeding behaviour, especially in the young stage, is not fully understood yet [
]. In a study [
], fingerlings (Figure 2) of this species exhibit three typical phases of feeding behaviour, namely aim, encounter and capture. Fingerlings subject to different duration of starvation exhibit different foraging behaviour. Soon Hock fingerlings subject to 1-day starvation are seen to display sit-and-wait predatory pattern. The usual foraging behaviour is hover search, where the fingerling will swim and then stay stationary before speeding towards prey. Under food deprivation, the fingerlings sneaked behind and chased prey through the water column. They attempted to catch every prey met in a single feeding action [
Soon Hock have distinct pairing mating behaviour [
]. However, not much is known about their mating behaviour. This species spawns at the beginning and end of each dry season. Sexual maturation occurs at an approximate length of 8 cm and fish at 15 to 30 cm can have 6,800 to 90,000 eggs [
Video 2. Soon Hock spawning in a recirculating aquaculture system (RAS) tank
This species can be found in many southeast Asian waters, such as Borneo, Sumatra, Thailand, Malaysia, the Philippines and Indonesia [
World map with distribution of Soon Hock (Map adapted from Owen Blacker; Creative Commons Attribution-NonCommercial 2.0 Generic License)
Larger view of distribution of Soon Hock in Southeast Asia (black dots)
This species was collected in various places in Singapore before, including Woodleigh, Sime Road forest, Lower Peirce Reservoir, Nee Soon Swamp forest, Lorong Banir, Sungei Seletar, Upper Seletar Reservoir, Sungei Punggol and Serangoon [
]. However, it is not limited to these mentioned places.
Soon Hock is a highly valued fish that is a delicacy to many countries in Asia, including Singapore. They are not only caught from the wild, but also reared in cages and ponds [
]. They are also frequently seen in restaurants and some supermarkets in Singapore.
Live soon hock in a restaurant tank (Photo: Sim Siying)
Steamed soon hock (Photo: Walter Lim; Creative Commons Attribution 2.0 Generic license)
Besides rearing them in cages, they are also cultured in more controlled environments in aquaculture systems because of disease problems when rearing them in cages and ponds. Most the the problems faced when rearing them in cages and outdoor pond systems are related to poor water quality and the lack of suitable control of the system [
]. Live tilapia is found to be a highly suitable feed for culturing Soon Hock [
Besides aquaculture, this species has also been used in aquaponics, which is a combination of aquaculture and hydroponics. Fish produce wastes which can be toxic to the fish themselves if they are not removed. However, the wastes can be nutrients to plants. Microbial breakdown of fish wastes or dissolved nutrients excreted by fish can be used by plants, which act as a filter, removing the wastes in the water [
A study on optimal tank design for a recirculating aquaponic system and the feed type given to the fish (Soon Hock in this case) was conducted [
]. Figure 3 shows one of the many different designs of an aquaponics system that can be used. This setup used Soon Hock and water spinach (
). Live food such as tilapia, as compared to minced fish (scads) produced less waste and gave the highest fish growth. Feed conversion efficiency was also the highest when the fish were fed with live food [
]. This means that the conversion of feed given to the fish resulted in the greatest growth in the fish and vegetables.
Figure 3. Schematic layout of recirculating aquaponic system (RAS) (Source: Lam et al., 2014; permission granted)
Soon Hock (
) is classified as Least Concern by the International Union for Conservation of Nature (IUCN) [
]. However, this species might be affected on a local scale by overfishing and pollution.
Potential threats on the environment
In South and Western Australia, this species is listed in the prohibited fish list [
]. It is against the law to possess or trade this fish without being authorised. This is because of the significant problem to the aquatic environment posed by this species in Australia [
], which may affect their native fish species.
Now found in both freshwater and brackish environments, Soon Hock occurred naturally only in brackish water habitats a few decades ago [
]. The colonisation of this fish in Singapore's freshwaters can be attributed to deliberate introduction by people [
]. This might have negative impacts on the native fish species, and thus the native biodiversity. Introduced fishes may direct affect native fish through predation, competition on food and habitat, diseases and parasites [
This species was first described in 1852 by Bleeker under the genus
]. There is a bracket beside the species name because the species was later moved to another genus, the genus
Etymology (origin of the name)
Greek, oxys = sharp + the name of a Nile fish, eleotris [
Vernacular (common name)
: Marble goby, Soon hock
(Bleeker, 1852) (misspelling);
(Bleeker, 1852) (misspelling) [
The hierarchical biological classification of this species can be seen in the table below.
Integrated Taxonomic Information System
This differentiation of this species from others will be covered in this section. Figure 4 might be useful in identifying the different parts of a fish.
Figure 4. Labelled diagram of a general fish morphology. (Source: Lim & Ng, 1990; permission pending)
The members of the family Eleotridae might be confused with members of the family Gobiidae because of many similar aspects. They can be distinguished by looking at their pelvic fins (Figure 4). Members of the family Eleotridae have separate pelvic fins (Figure 5) that do not fuse together to form a sucker, unlike members of the family Gobiidae (Figure 6) [
Figure 5. Pelvic fins separated in members of Eleotridae (Source: Inger & Chin, 2002; permission pending)
Figure 6. Pelvic fins united in members of Gobiidae. (Source: Inger & Chin, 2002; permission pending)
The base of the second dorsal fin in members of the family Gobiidae (Figure 7) is much longer than the distance between the end of the second dorsal fin to the base of the caudal fin. The lengths of the second dorsal fin base and the caudal peduncle are about the same in members of Eleotridae (Figure 8) [
Figure 7. Base of second dorsal fin longer than caudal peduncle in Gobiidae. (Source: Larson & Murdy, 2001, © FAO, 2001 Order Perciformes: Gobioidei, p. 3579, FAO Species Identification Guide for Fishery Purposes, downloaded on 23 October, 2014)
Figure 8. Base of second dorsal fin about the same as caudal peduncle in Eleotridae. (Source: Larson & Murdy, 2001, © FAO, 2001 Order Perciformes: Gobioidei, p. 3579, FAO Species Identification Guide for Fishery Purposes, downloaded on 23 October, 2014)
can be differentiated from other
species by looking at the caudal fin.
does not have black spots (ocelli) on its caudal base [
, another species in the same genus, has a black spot on the caudal base (Figure 9).
Figure 9. Oxyeleotris urophthalmus with red arrow pointing at the ocellus (Source: Fishes of Mainland Southeast Asia http://ffish.asia; under Creative Commons Attribution-NonCommercial 3.0 Unported License)
Screenshot of the original description (Source: Bleeker, 1852; public domain)
Refer to this link for the original description by Bleeker
The original description for this species was done by Bleeker [
]. It was first described under
, but was later moved to
. The description of the species was in Latin. The bottom paragraph in Dutch from the original description is the brief diagnosis on the differentiation of this species from another species in the genus
. "vooral door haar fraai met bruin en oranje gemarmerd en gewolkt ligchaam" is translated to "its beautifully marbled orange with brown lines body".
Figure 10. Arrow-shaped blotch at caudal peduncle. (Source: Fishes of Mainland Southeast Asia http://ffish.asia; under Creative Commons Attribution-NonCommercial License)
: The body is mostly dark brown above and pale brown underneath. The body generally has a series of large, dark blotches and the fins have black tinges alternating with white. The caudal peduncle, where the yellow arrow in figure 10 is, has a arrow-shaped blotch that points towards the head [
: A translucent membrane covers up the hard spines and/or soft rays, making up the fins of fish. Usually the spines are positioned nearer to the head if both spines and rays are present (Figure 10) [
: 7 in total
Dorsal soft rays
: 9 to 10
Anal soft rays
: 8 or 9 [
: 85 to 90 longitudinal series scales; 22 to 25 transverse series [
Counting fin rays and scales
: Elongate body with cylindrical, blunt head. The mouth is about the same width as the eyes [
: Longer caudal fin and caudal peduncle lengths in male [
Link to article on the sex determination in //Oxyeleotris marmorata// (Bleeker, 1852) based on morphometric features
: Largest recorded total length of 65 cm [
]. Commonly reaches total length of 30 cm [
of the genus
is Banjarmasin, South Kalimantan, Indonesia [
, one of the synonyms of
, is stored in the Academy of Natural Sciences of Drexel University (PANSP 86:67-163; Bangkok, 30 mi. up the Me Nam Chao Phya; collector deSchauensee).
There is high uncertainty in the phylogenetic relationship in bony fish and most of the knowledge about higher-level relationships among fish groups are based on morphology. With the influx of molecular studies, there are many studies done on phylogenetic relationships that have some differences in the results from morphological studies on phylogenetic relationships [
Taxonomy based on morphology is done by studying the external features of the specimen, such as the shape, size, colour, patterns. Observations on the internal appearance through dissections are also part of a morphological study. Read more about morphological taxonomy
. A molecular study is different from a morphological study in that it uses DNA and protein sequencing, that is now made possible by technology. Read more about molecular taxonomy
The order Perciformes is the largest vertebrate order and includes most marine fishes and also freshwater and brackish water groups. Approximately 23% of the species in the order Perciformes are gobioids (suborder Gobioidei). Gobioidei is
as confirmed by molecular phylogeny, and is consistent with morphological evidence [
]. From the analysis of molecular data, the family Eleotridae (excluding
, and including Xenisthmidae and Gobiidae) is monophyletic, corresponding to traditional taxonomy. The genus
is not monophyletic, where
is found outside the rest of the
species (Figure 11) [
Figure 11. Single most parsimonious phylogenetic hypothesis derived from analysis of ND1, ND2, COI and cyt b sequence data. Numbers on nodes are decay indices. Selected clades are labeled, including Gobioidei, OD (Odontobutidae plus Milyeringa), ED (Eleotridae plus Gobiidae and Xenisthmidae), BU (Butidae, not including Milyeringa, plus Gobiidae), and EN (Eleotrinae plusXenisthmidae). (Thacker & Hardman, 2005, permission obtained)
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