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Stiphodon ornatus MEINKEN, 1974

Rainbow Stiphodon

Etymology

Stiphodon: from the Greek στίφος (stifos), meaning ‘swarm, horde’, and ὀδών (odon), meaning ‘toothed’, in reference to the numerous, closely-packed teeth in the upper lip of member species.

ornatus: from the Latin ornatus, meaning ‘adorned, decorated’.

Classification

Order: Perciformes Family: Gobiidae

Distribution

Known only from the provinces of Aceh and West Sumatra, Sumatra, Indonesia.

Type locality is ‘Barung Belantai River, Sumatra, Indonesia’, which appears to correspond to a small river running close to a village named Barung Barung Belantai in West Sumatra province.

Western Sumatra appears to be the main source of Stiphodon species for the aquarium trade (Maeda and Tan, 2013) and this has aided in the positive identification of S. ornatus since its known range does not overlap with any similar-looking congener of which there are several (see ‘Notes’).

All Stiphodon in the aquarium trade are wild-collected and concerns have been raised regarding their conservation status since some are locally endemic and may already be threatened by habitat degradation, pollution or introduction of exotic species such as tilapia.

Habitat

Members of this genus are near-exclusive inhabitants of short coastal streams with habitats often lying above waterfalls or cataracts.

This makes them inaccessible to the majority of fishes although other gobiids and eleotrids often occur syntopically, sometimes alongside two or more Stiphodon species.

Amphidromous Macrobrachium spp. shrimp and neritid snails are the commonest invertebrates to be found.

The gradient of the streams varies depending on locality, and Stiphodon spp. inhabiting the fastest-flowing and/or living above waterfalls generally lack extended dorsalfin rays/spines plus the first dorsalfin is rounded in shape and approximately the same height as the second dorsalfin.

In contrast those possessing a ‘taller’ first dorsalfin with one or more extended rays (characters usually if not always more apparent in males) tend to live in slower-moving streams and not climb waterfalls as part of their life cycle (Watson, 2008).

S. ornatus falls into the latter group although details of its natural habitats have not made themselves available to date.

Substrates are normally of bedrock with scattered jumbles of rocks and boulders, and while riparian vegetation and submerged leaf litter are common aquatic plants aren’t usually present.

Evidence exists to suggest that different Stiphodon spp. actively choose a particular substrate type over another, with some appearing to focus on rocks or boulders within a particular size range for example.

The range of substrate sizes chosen by females also appears to be significantly narrower than that for males in some cases, so resource partitioning may be occurring between and/or within species depending on locality.

The most favourable habitats all contain very clear, well-oxygenated water which, allied with the tropical sun, facilitates the development of a rich biofilm carpeting submerged surfaces.

Sicydiines are such successful colonisers of these niche environments due to aspects of their morphology which allow them to both utilise this as a food source and employ a remarkable breeding strategy (see ‘Reproduction’).

Maximum Standard Length

65 – 70 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 80 ∗ 30 cm is the smallest recommended.

Maintenance

These gobies aren’t too difficult to keep provided some basic requirements are met.

Most importantly the water must be clean and well-oxygenated at all times so we suggest the use of either an over-sized filter, additional powerheads, flow pumps, or airstones.

Base substrate can either be of gravelsand, or a mixture of both to which should be added a layer of water-worn rocks and pebbles of varying sizes.

Aged driftwood can also be used but avoid new pieces since these usually leach tannins which discolour the water and reduce the effectiveness of artificial lighting which should be relatively strong in order to promote the growth of algae and associated micro-organisms (see ‘Diet’).

Some aquarists even maintain an open filter sponge in the tank to provide an additional food source.

If keeping multiple males of one or more species structure the rockwork to form plenty of potential hiding places and broken lines-of-sight to reduce the likelihood of excessive aggression.

Also bear in mind that males in particular tend to dig into the substrate when sleeping or spawning meaning larger rocks are best positioned directly on the tank base to prevent any risk of collapse.

They don’t sleep in the same burrow each night and females have been observed to occupy uninhabited ones.

Although not a feature of this species’ natural habitat aquatic plants can be used with hardier genera such as Microsorum, Crinum, and Anubias likely to fare best.

The latter are particularly useful as their leaves tend to attract algal growth and provide hiding places.

Since they need stable water conditions and feed on biofilm these fishes should never be added to immature set-ups and a tightly-fitting cover is necessary since they’re able to climb glass.

While weekly water changes of 30-50% tank volume are essential the rest of the tank needn’t be kept too clean and algae can be allowed to grow on all surfaces except the viewing pane.

Water Conditions

Temperature: 20 – 28 °C; increased surface agitation is needed to maintain dissolved oxygen levels towards the upper end of this range.

pH6.5 – 7.5

Hardness36 – 215 ppm

Diet

Stiphodon spp. are specialised grazers feeding on benthic algae plus associated micro-organisms and possess subterminal, extrusible mouthparts with dentition designed for the purpose including regenerative teeth.

The pelvic disc is also important not only to maintain position in rapidly-flowing water but also to provide leverage.

In the aquarium some sinking dried products and small, meaty foods such as live or frozen bloodworm may be accepted but should only be offered irregularly since the elongate gut is specifically designed to process vegetable matter.

For long-term success it’s thus essential to provide a mature aquarium with a plentiful supply of algae-covered rocks and other surfaces.

If unable to grow sufficient algae in the main tank or you have a community containing numerous herbivorous fishes which consume what’s available quickly, it may be necessary to maintain a separate container in which to grow algae on rocks and switch them with those in the main tank on a cyclical basis.

Such a ‘nursery‘ doesn’t have to be very large, requires only strong lighting and in sunny climates can be kept outdoors.

Algal type is also important with diatomscyanobacteria (commonly referred to as blue-green ‘algae‘) and green varieties preferred to tougher ones like rhodophytic ‘black brush’ algae.

Unfortunately as a result of their specialised diet and oxygen requirements Stiphodon spp. are regularly seen on sale in an emaciated state which can be tricky to correct.

A good dealer will have done something about this prior to sale but if you decide to take a chance with severely weakened specimens they’ll initially require a readily-available source of suitable foods in the absence of competitors if they’re to recover.

Behaviour and CompatibilityTop ↑

Stiphodon spp. can be kept in a community provided tankmates are chosen with care.

Peaceful, similarly-sized species which naturally inhabit well-oxygenated streams such as Tanichthys, Microdevario, or smaller Danio species are the best choices for the upper levels, but we’ve also seen it being maintained with various characins, small poeciliid livebearers, and freshwater shrimp of the genera Caridina and Neocaridina.

Other bottom-dwellers can include small loaches from genera such as Gastromyzon, Pseudogastromyzon, Barbucca, or Acanthopsoides, and in high-turnover set-ups obligate torrent-dwellers like Annamia, Homaloptera, etc.

Avoid those that feed aggressively such as many Schistura spp.

Bigger fishes are best omitted entirely although in large set-ups it may be possible to add a few non-predatory, surface-dwelling species, while the majority of cichlids and other territorial fishes inhabiting the lower reaches should be avoided entirely.

Males tend to be loosely territorial, especially when breeding, but several can be kept together provided sufficient space and suitable foods are available, and other stream-dwelling gobies such as Sicyopus, Sicyopterus, Rhinogobius, or Schismatogobius spp. also make good companions.

Though males aren’t necessarily gregarious females tend to exist in loose groups meaning a single male with two or more females is the recommended minimum purchase.

Females of different species will group together but males appear able to differentiate between them.

Sexual Dimorphism

As with all members of the genus sexual dimorphism is pronounced, though in this case males are hard to define.

Base body colouration varies from pale olive to dark brown with dark-edged scales but they’re capable of rapidly changing to a much darker patterning, and the degree to which this occurs is also highly variable (see images for examples).

While some specimens remain dark much of the time once settled into the aquarium, others switch between dark and light colouration, are only dark rarely, or even not at all.

Cheek colouration can be orange or gold to vivid blue and is easily distorted by flash photography.

Basic fin colouration is orange/red with dark rays, the second dorsal, anal, and distal portion of the caudal-fin are bordered in whitish blue and all the fins contain irregular rows of dark markings and chromatophores.

In dark individuals the finnage also tends to darken and can appear completely black with just a thin orange to bluish border in extreme cases.

Females are relatively plain and similar in appearance to those of some other species with a pale base colouration and two dark, lateral body stripes.

The latter have relatively uniform, straight edges compared with most other species, especially in the anterior portion of the body.

Two additional thin dark stripes run over the head and dorsal surface, merging into one around the second dorsal-fin and meeting the upper body stripe on the caudal peduncle.

When an individual is stressed or excited colouration pales considerably, the body scales appear edged in black, the fins contain irregular rows of black markings and in some specimens, lighter chromatophores.

Reproduction

Observations of courtship behaviour and the occasional spawning exist but to date no-one has managed to raise fry of any Stiphodon spp. in captivity.

This is undoubtedly attributable to their complex amphidromous breeding strategy in which adults live and spawn in freshwater streams but the initially pelagic post-hatch larvae are washed downstream to the sea where the post-larval fry spend the first part of their life developing in marine conditions.

Once they reach a certain stage of development they begin to migrate upstream, a journey which sometimes includes spectacular climbs up and over waterfalls or other obstructions.

Females are extraordinarily fecund for their size and can deposit as many as 10,000 eggs in a single spawning event.

These are tiny (~ 0.5 mm in diameter), pyriform, and attached to solid surfaces by filaments, normally being placed on the underside of rocks.

It’s thought that reduced egg size and high fecundity are advantageous since the large number of fry offsets risks such as predation or the possibility of excessive dispersal at sea and their small size allows them to feed on microscopic plankton.

Spawning is initiated by the intensely-coloured male as he attempts to coax females to his chosen spawning site while fending off rivals.

It usually occurs under rocks and captive males have also been observed to dive head first into the substrate followed by a female at the climax of courtship.

Once fertilised the mass of eggs, which can number in the thousands, is guarded by the male during the incubation period of less than 24 hours in studied cases.

The fry hatch as undeveloped larvae with a large yolk sac attached and lacking a mouth, anus, or functioning eyes.

The yolk sac is absorbed in 3-4 days and during that period they must reach the ocean, probably the reason why incubation is short as early hatching gives them a better chance of success.

The fact that Stiphodon spp. are only found in relatively short, steep streams is also thought related to this downstream dispersal.

The larvae initially exist among the plankton in a pelagic form before coming to settle on the substrate within the shallow surf zone.

In one study the pelagic larvae of S. percnopterygionus were found to be transparent and possess an emarginate caudal-fin whereas ‘settled’ larvae (those no longer swimming in the water column) were pigmented.

Interestingly the range of standard length for the pelagic larvae (13.5 – 14.2 mm) was greater than that of settled larvae (12.7 – 13.6 mm).

The pelagic larval duration (PLD) i.e. the length of the larval phase was found to vary between 78 – 146 days and be longer at colder temperatures.

During the annual cool spell between December and April the activity of the gonads reduces considerably in both sexes and the fish probably stop breeding while peak breeding season is June – November.

Once settled on the substrate the larvae begin to lose their temporary specialisations such as the emarginate caudal-fin and begin their journey upstream to join the adults.

They may need to travel several kilometres inland, often over cascades or through stretches of rapidly-flowing water.

The pelvic fins are fused into a disc designed for suction which allow the juveniles to adhere to hard surfaces and climb steep gradients, in some cases even ascending vertical waterfalls with overhanging rocks.

This journey can take several months but the fish are sexually mature within a year and since their natural lifespan is only thought to be around two years are likely to begin spawning soon after, if not immediately, on arrival to the breeding grounds.

Amphidromy in sicydiine gobies isn’t unique to members of Stiphodon and is displayed by all other genera.

McDowall (2007) gave a list of potential benefits to fishes employing such a breeding strategy, hypothesising that it may facilitate colonisation of new islands emerging in volcanic areas and/or allow recolonisation of streams following events such as volcanic eruptions/rapid changes in water flow during the wet season.

He also considered that leaving the marine environment can be seen as a trade-off in that since amphidromous gobies are often the only fishes found in their habitats predators are virtually non-existent, but the available food sources are far less diverse than in the ocean.

The ability to graze biofilm appears to be essential for success.

NotesTop ↑

This species is traded as S. sp. ‘rainbow’, S. sp. ‘gold fin‘, or S. sp. ‘gold cheek’ and is among the more widely-available members of the genus although its identity was unclear prior to 2013.

The most commonly-traded fish certainly appears to be S. ornatus (K. Maeda pers. comm., also see comments in ‘Distribution’ section above) but there may be more than one species involved with a smaller, near-identical variant traded under the same names, and males of both ‘forms’ can also display a remarkable amount of mood-dependant colour variation.

This has made identification tricky because S. ornatus closely resembles the congeners S. atratus, S. imperiorientis, S. martenstyni, S. pelewensis, S. pulchellus, and S. weberi and little information is available regarding live colouration and morphological differences between them.

S. ornatus can be diagnosed by the following combination of characters as per Maeda and Tan (2013): usually 9 soft second dorsal-fin rays; usually 15 pectoral-fin rays; first dorsal-fin in male pointed with spines 3-5 elongate; male with large caudal-fin measuring 29-35 % SL; 33-45 premaxillary teeth in specimens <50.0 mm SL, 44-47 in ≥ 50.0 mm SL); no white patch behind pectoral-fin base in males; posterior half of occipital region always with cycloid scales in both males and females; male usually with 7–11 obscure dusky transverse bars laterally on posterior portion of body and caudal-fin, sometimes with two broad dusky bars laterally below the first and second dorsal-fin bases;  6–12 black spots on longest pectoral-fin ray in male, 0–6 in female.

The Gobiidae is the most speciose vertebrate family and notoriously problematic in terms of identifying fishes down to species level.

Stiphodon is often included in the putative subfamily Sicydiinae which currently contains at least six other generaCotylopusLentipesParasicyidiumSicydiumSicyopus, and Sicyopterus.

Sicyopus and Lentipes species are omnivorous or carnivorous whereas the others are mostly herbivorous.

All share a similar life-history with many endemic to a particular island or group of islands, though a few are widespread.

They also share some morphological characters including pelvic fins modified into a sucking disc with a strong spine and thickened, highly-branched rays, at the posterior edge of which the pelvic-fin spines and first ray are joined by a membrane forming ‘fleshy pads’ at the tips of the spines.

The tongue is fused to the base of the mouth, a feature shared by some other gobiids.

Following the work of Koumans (1953) Stiphodon was considered a monotypic genus containing only S. elegans for almost half of the twentieth century, despite S. semoni being the original type species, but since the late 1980s a number of species have been described or revalidated.

Over 30 species have been described to date with at least a similar number awaiting description (Watson, per. comm.), and while traditionally considered confined to the tropical Indo-Pacific region they’re also found in the eastern Indian Ocean with Sri Lanka representing the known limit of their range.

They can be separated into two generalised groups based on male morphology; those with a first dorsal-fin approximately the same height as the second, e.g., S. atropurpureusS. semoni, etc., and those in which the first dorsal-fin contains extended, sometimes filamentous spines or rays, e.g., S. percnopterygionusS. atratusS. elegans.

Some species also exhibit a patch of white, fatty tissue behind the pectoral-fin in males. The function of this is unknown but it appears to be related to male dominance in some way, with older adults possessing larger patches of tissue (Watson, 2008).

The fused pelvic fins form a structure normally referred to as the pelvic disc, a common feature among gobiids which is used to adhere to rocks and other submerged surfaces.

In Sicyopus and Stiphodon this is short-based and attached to the belly only between the fifth pair of fin rays whereas in other sicydiines it’s attached between all five rays (Watson, 2005).

The role of the disc in ascending waterfalls and cascades has given rise to the common names of ‘rock-climbing’ or ‘cling’ gobies for members of the Sicydiinae in general.

They’re also sometimes referred to as ‘toothed-lip’ gobies in reference to the outwardly-orientated, replaceable teeth of the upper jaw.

Many of those being imported for the aquarium trade have proven difficult to identify for a number of reasons including:

– taxonomic confusion.
– lack of aquarium literature.
– incorrect labelling by exporters and subsequently shops.
– historical over-use of some names.
– likely trade of undescribed species without locality data.
– mixing of species at export facilities.

References

  1. Keith, P., G. Marquet, and M. Pouilly, 2009 - Publications Scientific du Muséum d'Histoire Naturelle, Paris 31 (3): 471-483
    Stiphodon mele n. sp., a new species of freshwater goby from Vanuatu and New Caledonia (Teleostei, Sicydiinae), and comments about amphidromy and regional dispersion.
  2. Maeda, K. and H. H. Tan, 2013 - The Raffles Bulletin of Zoology 61(2): 749-761
    Review of Stiphodon (Gobiidae: Sicydiinae) from western Sumara, with description of a new species.
  3. McDowall, R. M., 2009 - Reviews in Fish Biology and Fisheries 19(1): 1-8
    Early hatch: a strategy for safe downstream larval transport in amphidromous gobies.
  4. McDowall, R. M., 2007 - Fish and Fisheries 8(1): 1-13
    On amphidromy, a distinct form of diadromy in aquatic organisms.
  5. Parenti, L. R., and K. R. Thomas, 1998 - Journal of Morphology 237(3): 257-274
    Pharyngeal Jaw Morphology and Homology in Sicydiine Gobies (Teleostei: Gobiidae) and Allies.
  6. Watson, R. E., 2008 - Zootaxa 1715: 43-56
    A new species of Stiphodon from southern Sumatra (Pisces: Gobioidei: Sicydiinae).
  7. Watson, R. E., 1995 - Ichthyological Exploration of Freshwaters 6(1): 33-48
    Gobies of the genus Stiphodon from French Polynesia, with descriptions of two new species (Teleostei: Gobiidae: Sicydiinae).
  8. Watson, R. E. and I-S. Chen, 1998 - Aqua, Journal of Ichthyology and Aquatic Biology 3(2): 55-68
    Freshwater gobies of the genus Stiphodon from Japan and Taiwan (Teleostei: Gobiidae: Sicydiini).
  9. Watson, R. E. and M. Kottelat, 1995 - Ichthyological Exploration of Freshwaters 6(1): 1-16
    Gobies of the genus Stiphodon from Leyte, Philippines, with descriptions of two new species (Teleostei: Gobiidae: Sicydiinae).
  10. Yamasaki, N. and K. Tachihara, 2006 - Icthyological Research 53(1): 13-18
    Reproductive biology and morphology of eggs and larvae of Stiphodon percnopterygionus (Gobiidae: Sicydiinae) collected from Okinawa Island.
  11. Yamasaki, N., K. Maeda and K. Tachihara, 2007 - Raffles Bulletin of Zoology Supplement 14: 209-214
    Pelagic larval duration and morphology at recruitment of Stiphodon percnopterygionus (Gobiidae: Sicydiinae).

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