Iksookimia koreensis (KIM, 1975)

SynonymsTop ↑

Cobitis koreensis Kim, 1975

Etymology

koreensis: named for Korea, to which this species is endemic.

Classification

Order: Cypriniformes Family: Cobitidae

Distribution

All Iksookimia species are endemic to Korea, with I. koreensis among the more widely-distributed.

It was described from ‘Jojong River, tributary of the Han River, at Sang-myon, Gapyong-gun, Gyong gi-do, South Korea’, but is relatively common in river drainages of northern and western South Korea.

Habitat

This species apparently shows a preference for small, shallow rivers and streams with moderate to fast currents.

Substrates are normally composed of smaller rocks, sand and gravel with jumbles of boulders, and while riparian vegetation and patches of submerged leaf litter are common features aquatic plants aren’t usually present.

The most favourable habitats contain clear, oxygen-saturated water which facilitates the development of a rich biofilm carpeting submerged surfaces during warmer periods.

The climate of South Korea is characterised by cold, dry winters and hot, humid summers with spring and autumn essentially non-existent.

I. koreensis tends not to feed much during colder months when it enters a period of semi-hibernation.

Maximum Standard Length

100 – 130 mm.

Aquarium SizeTop ↑

An aquarium with base measuring 100 ∗ 30 cm should be the smallest considered.

Maintenance

Most importantly the water must be clean and well-oxygenated so we suggest the use of an over-sized filter as a minimum requirement.

Turnover should ideally be 10-15 times per hour so additional powerheads, airstones, etc. should be employed as necessary.

Base substrate can either be of gravel, sand or a mixture of both to which should be added a layer of water-worn rocks and pebbles of varying sizes, and perhaps some driftwood roots and branches.

Although rarely a feature of the natural habitat aquatic plants can be used with adaptable genera such as Microsorum, Crinum and Anubias spp. likely to fare best. The latter are particularly useful as their leaves tend to attract algal growth and provide additional cover.

Since it requires stable water conditions this species should never be added to a biologically immature set-up, and regular partial water changes are essential.

Water Conditions

Temperature: For general care 20 – 24 °C is recommended but it should withstand warmer conditions provided dissolved oxygen levels are maintained.

pH: 7.0 – 8.0

Hardness: 90 – 268 ppm

Diet

Chiefly a micropredator feeding on chironomid larvae and benthic inveretebrates in nature.

In the aquarium it will accept sinking dried foods but should also be offered regular meals of small live and frozen fare such as Daphnia, Artemia, bloodworm, etc. A varied diet is key to maintaining it in the best of health.

Behaviour and CompatibilityTop ↑

Iksookimia spp. are peaceful both with one another and other fishes and there exist no reports of them harming tankmates though they may prey on eggs or fry.

They fare best in the presence of conspecifics and should ideally be kept in a group of 4 or more specimens.

I. hugowolfeldi makes an excellent addition to communities of suitably-sized stream-dwelling fishes. Good tankmates include small, peaceful cyprinids plus current-loving loaches from genera such as Gastromyzon, Pseudogastromyzon, Beaufortia, Sewellia, and peaceful nemacheilids.

Rheophilic gobies from genera including Sicyopterus, Stiphodon, Rhinogobius, and Lentipes can also make interesting additions to this kind of community.

Territorial or otherwise aggressive bottom-dwellers such as most substrate-dwelling cichlids and some nemacheilid loaches are less-suitable companions.

Sexual Dimorphism

In mature males the first pectoral-fin ray is extended and there is a thickened structure known as the lamina circularis at the base of the second.

Adult females are typically heavier-bodied and a little larger then males.

Reproduction

Presumably a seasonal spawner in nature but hasn’t been bred in captivity as far as we know.

NotesTop ↑

This species may not yet have reached the western hobby but is sometimes traded in Korea and Japan, and is one of five currently-recognised members of the genus alongside I. koreensis, I. longicorpa, I. pumila and I. yongdokensis.

Among them it’s most similar to I. pumila which was initially described as a subspecies but is now considered distinct.

The two are most easily-separated by colour pattern; I. koreensis has 10 or more dark bars along each flank, a series of saddle-like markings along the dorsal surface and the entire upper body is peppered with irregular spots whereas I. pumila has less than 10 bars on the flanks and lacks spots in the upper body.

It appears that I. hugowolfeldi, I. longicorpus and I. yongdokensis form a distinct biogeographic lineage to I. koreensis and I. pumila, with the former group distributed to the south of the Taebaek and Noryeong moutnain ranges and the latter to the west.

This is further evidenced by the fact that the lamina circularis in males of the southern group is rounded in shape while that of the western species is more elongate.

Iksookimia was erected by Nalbant (1993) to accommodate five species of Cobitis from Korea. The description of I. yongdokensis in 1997 increased the number of members to six but C. choii was later reassigned to its original status.

We haven’t seen Nalbant’s paper but a brief summation by Kim and Park (1997) states that he separated Iksookimia spp. on the basis of a combination of characters including: elongate first pectoral ray; relatively stout body form; longer barbels; more developed mental lobes; reduced sub-ocular spine; scales with a larger ‘focal’ area; absence of four ‘Gambetta’ pigmentation zones on the flanks.

This analysis was supported by Kim (2009) who noted the same characters while adding that the lateral line does not extend beyond the pectoral fins and that the second pectoral ray has a ‘beak-like tip’ while also placing Cobitis pacifica into Iksookimia.

The family Cobitidae, often referred to as ‘true’ loaches, is widely-distributed across most of Eurasia with the Indian subcontinent, Southeast Asia and China representing particular centres of species diversity.

Phylogenetic analyses by Tang et al. (2006), Šlechtová et al. (2007) and Šlechtová et al. (2008) revealed that the group constitutes a separate genetic lineage to the family Botiidae (the two were previously grouped together under Cobitidae as subfamilies Cobitinae and Botiinae).

In the most recent study Iksookimia was found to represent a polyphyletic grouping comprising up to three separate genetic lineages.

The authors stopped short of rearranging the genus, instead provisionally including it in one of four generalised lineages within a ‘northern’ clade of the family Cobitidae comprising species distributed in Europe, western, northern and eastern Asia, Vietnam and Laos. These are as follows:

1) All species of Sabanjewia.
2) Microcobitis misgurnoides.
3) All Misgurnus, Paramisgurnus and Koreocobitis spp.
4) All Cobitis spp. plus Iksookimia, Niwaëlla and Kichulchoia spp.

All cobitids possess sharp, motile, sub-ocular (below the eye) 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, in larger species, break human skin.

References

1. Jang, M.-H., J.-D. Yoon, J.-H. Shin, and G.-J. Joo, 2008 - Aquatic Conservation: Marine and Freshwater Ecosystems 18(6): 819-828
   Status of freshwater fish around the Korean Demilitarized Zone and its implications for conservation.
2. Kim, I.-S., 2009 - Korean Journal of Ichthyology 21 (Suppl.): 7-28
   A review of the spined loaches, family Cobitidae (Cypriniformes) in Korea.
3. Kim, I.-S. and J.-Y. Park, 1997 - Ichthyological Research 44(3): 249-256
   Iksookimia yongdokensis, a new cobitid fish (Pisces: Cobitidae) from Korea with a key to the species of Iksookimia.
4. Kottelat, M, 2012 - Raffles Bulletin of Zoology Supplement 26: 1-199
   Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei).
5. Tang, Q., H. Liu, R. Mayden and B. Xiong, 2006 - Molecular Phylogenetics and Evolution 39(2): 347-357
   Comparison of evolutionary rates in the mitochondrial DNA cytochrome b gene and control region and their implications for phylogeny of the Cobitoidea (Teleostei: Cypriniformes).
6. Šlechtová, V., J. Bohlen and A. Perdices, 2008 - Molecular Phylogenetics and Evolution 47(2): 812-831
   Molecular phylogeny of the freshwater fish family Cobitidae (Cypriniformes: Teleostei): delimitation of genera, mitochondrial introgression and evolution of sexual dimorphism.
7. Šlechtová, V., J. Bohlen and H. H. Tan, 2007 - Molecular Phylogenetics and Evolution 44(3): 1358-1365
   Families of Cobitoidea (Teleostei; Cypriniformes) as revealed from nuclear genetic data and the position of the mysterious genera Barbucca, Psilorhynchus, Serpenticobitis and Vaillantella.