Syncrossus hymenophysa (BLEEKER, 1852)

Green Tiger Loach

Classification

Order: Cypriniformes Family: Botiidae

Distribution

Described from close to the city of Palembang, therefore presumably the Musi River basin, South Sumatra province, Sumatra, Indonesia, and since recorded from elsewhere on Sumatra plus the Malaysian state of Sarawak and Indonesian province West Kalimantan on Borneo.

It’s also known from the Pahang and Perak river systems in Peninsular Malaysia but it may already have disappeared there given that only a single confirmed specimen has been documented since 1955, while possible occurrences on Java also remain in doubt.

Habitat

S. hymenophysa has been recorded in various habitat types from small, upland, headwater streams to main river channels and lakes. During the wet season it migrates into flooded areas to feed and spawn meaning it’s found in different biotopes depending on the time of year.

The habitats themselves also vary; water flow and depth tend to increase significantly during the wet season, for example. Turbidity and pH typically also rise during this time while water temperature drops. According to Kottelat and Widjanarti (2005) it’s often associated with submerged objects such as tree branches, roots, floating logs, or structural components of housing.

In the highly diverse Danau Sentarum National Park in the Kapuas River basin, West Kalimantan, Borneo this species occurs sympatrically with over 200 other taxa including Barbonymus schwanenfeldii, Crossocheilus oblongus, Cyclocheilichthys janthochir, Epalzeorhynchos kalopterus, Paracrossochilus vittatus, ‘Puntius‘ endecanalis, ‘P.‘ everetii, ‘P.‘ kuchingensis, ‘P.‘ trifasciatus, Rasbora caudimaculata, R. cephalotaenia, R. sarawakensis, R. trilineata, Trigonopoma gracile, T. pauciperforatum, Homaloptera nebulosus, H. orthogoniata, Nemacheilus saravacensis, N. spiniferus, Vaillantella cinnamomea, Chromobotia macracanthus, Pangio semicincta, Hemibagrus wyckii, Mystus castaneus, M. singaringan, Kryptopterus bicirrhis, Datnioides microlepis, Nandus nebulosus, Helostoma temminkii, Channa pleurophthalma, and Mastacembelus erythrotaenia.

Maximum Standard Length

150 – 210 mm.

Aquarium SizeTop ↑

Minimum base dimensions of 150 ∗ 45 cm or equivalent are required for long-term care.

Maintenance

All botiids need a well-structured set-up although the actual choice of décor is more-or-less down to personal taste. A natural-style arrangement could include a substrate of sand/fine gravel with lots of smooth, water-worn rocks and pebbles plus one or two lumps of driftwood or twisted roots/branches.

Lighting can be relatively subdued and plants able to grow in such conditions like Microsorum, Taxiphyllum barbieri, or Anubias spp. can be added if you wish. These have an added benefit as they can be attached to pieces of décor in such a way as to provide useful shade.

Otherwise be sure to provide plenty of cover as Syncrossus spp. are inquisitive and seems to enjoy exploring their surroundings. Rocks, wood, flower pots and aquarium ornaments can be used in whichever combination to achieve the desired effect.

Bear in mind that these loaches like to squeeze themselves into small gaps and crevices so items with sharp edges should be omitted, and any gaps/holes small enough for a fish to become trapped should be filled in with aquarium-grade silicone sealant. A tightly-fitting cover is also essential as they may also jump at times.

Although botiids don’t require the very turbulent conditions favoured by many balitorids/nemacheilids they do best when the water is well-oxygenated with a degree of flow, are intolerant to accumulation of organic wastes, and requires spotless water in order to thrive. For this reason they should never be introduced to biologically immature set-ups and adapt most easily to stable, mature aquaria. In terms of maintenance weekly water changes of 30-50% tank volume should be considered routine.

Water Conditions

Temperature: 25 – 30 °C

pH: 5.0 – 7.5

Hardness: 18 – 215 ppm

Diet

While Syncrossus spp. appear to be chiefly carnivorous by nature they will also eat vegetative matter if available, sometimes including soft-leaved aquatic plants.

They’re largely unfussy feeders but should be offered a varied diet comprising quality dried products, live/frozen bloodworm, Tubifex, Artemia, etc. plus fresh fruit and vegetables such as cucumber, melon, blanched spinach, or courgette.

Chopped earthworm can also provide a useful source of protein but should be used sparingly, while home-made, gel-based foods using a mixture of natural ingredients are highly recommended. They’ll also prey on aquatic snails but should not be considered the answer to an infestation since if other options are available they will take them. Once settled into an aquarium they’re bold feeders, often rising into midwater.

Behaviour and CompatibilityTop ↑

Can be belligerent and should not be kept with much smaller fishes as they may be intimidated by its size and sometimes very active behaviour. Slow-moving, long-finned species such as ornamental bettas, guppies, and many cichlids should also be avoided as trailing fins can be nipped.

More suitable choices are fast-moving, pelagic cyprinids such as many Devario, Rasbora, ‘Puntius‘, Mystacoleucus, and some Danio spp., while in larger tanks the genera Barilius, Luciosoma, Balantiocheilos, and Barbonymus are options.

In terms of bottom-dwellers it’s often said to do well alongside other robust botiid species though experiences tend to vary with some reporting excessive aggression. Some cobitid/nemacheilid loaches are also possibilities as are members of Epalzeorhynchos, Crossocheilus, and Garra plus many non-territorial catfishes. As always, thorough research prior to selecting a community of fishes is the best way to avoid problems.

These loaches are gregarious, form complex social hierarchies and should be maintained in groups of at least 5 or 6 specimens, preferably 10 or more. When kept singly they can become withdrawn or aggressive towards similarly-shaped fishes, and if only a pair or trio are purchased the dominant individual will typically attack the other(s) repeatedly and may prevent them from feeding.

That said most botiids require regular contact with conspecifics, a fact exemplied by a number of behavioural rituals which have been recorded consistently in aquaria (see ‘Notes’).

Sexual Dimorphism

Adult females should be noticeably stockier than males and probably grow larger, too. Other differences have yet to be documented as far as we know.

Reproduction

Appears not to have been bred in aquaria. Presumably a seasonal, migratory spawner in nature.

NotesTop ↑

This species is sometimes confused with S. helodes, native to Thailand, Laos, Cambodia and southern Vietnam, but differs in several ways, most obviously possession of a dark spot in the dorsal-fin and lack of small, dark markings in the lower half of the body. It also has 12-15 vertical body bars with bluish borders vs. 10-12 bars without bluish borders in S. helodes.

Syncrossus is told apart from other botiid genera by possession of a unique, sickle-shaped anterior process on the premaxilla which surrounds a cavity between the left and right processes, plus the rostral process is short with no ridge along the inner edge.

Members can be further distinguished via the following combination of characters: the mental lobe is not developed into a barbel and has a pair of fleshy papillae at the anterior edge; the fronto-parietal fontanelle is large and wide; the anterior chamber of the gas bladder is partially covered by a bony capsule and the posterior chamber is large; the top of the supraethmoid is narrow; the optic foramen is large; the suborbital spine is not strongly curved backwards, and has a bifid structure; the head is naked (based on Taki, 1972: 74, 76); the colour pattern consists of regular, narrow bars while some species possess additional, longitudinal rows of black spots.

The family Botiidae was first proposed as a genetically distinct grouping by Nalbant (2002) having previously been considered a subfamily (Botiinae) of the family Cobitidae. Nalbant also moved some previous members of Botia into the new genus Yasuhikotakia based on a number of morphological characters.

Later Kottelat (2004) made further modifications to the taxonomy, raising the new genus Chromobotia for B. macracanthus and confirming that species previously included in the genus Hymenophysa should instead be referred to Syncrossus.

The former alteration was based on colour pattern plus some morphological characters and the latter because Hymenophysa not only represents a spelling mistake (McClelland’s original spelling was Hymenphysa) but is a junior synonym of Botia. As a result of these works the family Botiidae thus includes seven genera divided into two tribes within which Botia appears to be the most basal lineage:

Tribe Leptobotiini – Leptobotia, Parabotia, Sinibotia.
Tribe Botiini – Botia, Chromobotia, Syncrossus, Yasuhikotakia.

Phylogenetic studies by Tang et al. (2005) and Šlechtová et al. (2006) have largely confirmed this system to be correct although the latter disagreed with the placement of Sinibotia, finding it to be more closely related to the tribe Botiini.

Interestingly, Yasuhikotakia nigrolineata and Y. sidthimunki were found to be more closely-related to both Sinibotia and Syncrossus than other species of Yasuhikotakia, though no nomenclatural changes were actioned with the need for more detailed study given as reasoning. Šlechtová et al. also proposed the use of subfamily names under the following system:

Subfamily Leptobotiinae – Leptobotia, Parabotia.
Subfamily Botiinae – Botia, Chromobotia, Sinibotia, Syncrossus, Yasuhikotakia.

Within these Botia appears to be the basal, i.e., most ancient lineage and in a more-detailed phylogenetic analysis Šlechtová et al. (2007) confirmed the validity of the family Botiidae with all genera listed above as members rather then being grouped into subfamilies. This latter, simplified, system is the one we currently follow here on SF.

Some behavioural routines exhibited by Syncrossus spp. have been recorded often enough that they’ve been assigned non-scientific terms for ease of reference. For example during dominance battles (these occur most frequently when the fish have been introduced to a new tank, or new individuals added to an existing group) the protagonists normally lose much of their body patterning and colouration, a phenomenon that’s come to be known as ‘greying out’. Such displays will sometimes also happen within an established group as individuals seek to improve social ranking but are usually nothing to worry about.

Interestingly some observations suggest that the character of the highest-ranked, or alpha, fish appears to affect that of the whole group though it must be said that scientific studies of botiid loach behaviour are virtually non-existent. It certainly seems that they display a degree of ‘personality’ with some specimens being naturally bolder/more aggressive than others. The alpha is normally the largest specimen within the group and often female.

Sound also appears to be an important factor in communication since these loaches are able to produce audible clicking sounds, these increasing in volume when the fish are excited. The behavioural aspects of this phenomenon remain largely unstudied but the sounds are thought to be produced by grinding of the pharyngeal teeth.

All Syncrossus spp. possess sharp, motile, sub-ocular spines which are normally concealed within a pouch of skin but erected when an individual is stressed, e.g., if removed from the water. Care is therefore necessary as these can become entangled in aquarium nets and with larger specimens in particular break human skin.

Botiids are also susceptible to a condition commonly referred to as ‘skinny disease’ and characterised by a loss of weight. This is especially common in newly-imported specimens and is thought to be caused by a species of the flagellate genus Spironucleus. It is treatable although the recommended medication varies depending on country. Hobbyists in the UK tend to use the antibiotic Levamisole and those in the United States Fenbendazole (aka Panacur), for example.

References

1. Bleeker, P., 1852 - Natuurkundig Tijdschrift voor Nederlandsch Indië v. 3: 569-608
   Diagnostische beschrijvingen van nieuwe of weinig bekende vischsoorten van Sumatra. Tiental I - IV.
2. Alfred, E. R., 1961 - Bulletin of the Raffles Museum 30: 32-37
   Notes on a re-examination of some Bleeker type specimens of Indo-Malayan fresh-water fishes. Part 1, Cobitidae and Homalopteridae.
3. Grant, S., 2007 - Ichthyofile Number 2: 1-106
   Mainland fishes of the genus Syncrossus Blyth, 1860 (Teleostei: Botiidae).
4. Kottelat, M., 1998 - Ichthyological Exploration of Freshwaters 9(1): 1-128
   Fishes of the Nam Theun and Xe Bangfai basins, Laos, with diagnoses of twenty-two new species (Teleostei: Cyprinidae, Balitoridae, Cobitidae, Coiidae and Odontobutidae).
5. Kottelat, M., 2004 - Zootaxa 401: 1-18
   Botia kubotai, a new species of loach (Teleostei: Cobitidae) from the Ataran River basin (Myanmar), with comments on botiine nomenclature and diagnosis of a new genus.
6. Kottelat, M. and E. Widjanarti, 2005 - Raffles Bulletin of Zoology Supplement 13: 139-173
   The fishes of Danau Sentarum National Park and the Kapuas Lakes area, Kalimantan Barat, Indonesia.
7. Nalbant, T. T., 2002 - Travaux du Museum d'Histoire Naturelle : 309-333
   Sixty million years of evolution. Part one: family Botiidae (Pisces: Ostariophysi: Cobitoidea).
8. Nalbant, T. T., 2004 - Travaux du Museum d'Histoire Naturelle : 269-277
   Hymenphysa, Hymenophysa, Syncrossus, Chromobotia and other problems in the systematics of Botiidae. A reply to Maurice Kottelat.
9. Parenti, L. R. and K. K. P. Lim, 2005 - Raffles Bulletin of Zoology Supplement 13: 175-208
   Fishes of the Rajang basin, Sarawak, Malaysia.
10. Roberts, T. R., 1989 - Memoirs of the California Academy of Sciences 14: i-xii + 1-210
    The freshwater fishes of Western Borneo (Kalimantan Barat, Indonesia).
11. Tan, H. H. and M. Kottelat, 2009 - Ichthyological Exploration of Freshwaters 20(1): 13-69
    The fishes of the Batang Hari drainage, Sumatra, with description of six new species.
12. Tang, Q., B. Xiong, X. Yang and H. Liu, 2005 - Hydrobiologia 544(1): 249-258
    Phylogeny of the East Asian botiine loaches (Cypriniformes, Botiidae) inferred from mitochondrial cytochrome b gene sequences.
13. Šlechtová, V., J. Bohlen, J. Freyhof, and P. Ráb., 2006 - Molecular Phylogenetics and Evolution 39(2): 529-541
    Molecular phylogeny of the Southeast Asian freshwater fish family Botiidae (Teleostei: Cobitoidea) and the origin of polyploidy in their evolution.