Hong Kong's Freshwater Fish: Who Cares?!?

More about Hong Kong freshwater fishes

Yaoshanicus no more, but Nicholsicypris galore!

Even more about Hong Kong freshwater fishes

Hong Kong's Freshwater Fish: Who Cares?!?

by Bosco Chan

An on-going survey of the ichthyofauna in lowland waterways, as part of my Ph.D. study concerning the environmental effects of channelization in Hong Kong, has revealed the desperate need for such studies. Twenty-two lowland watercourses, of different sizes and various degrees of human impacts, have so far been visited. A total of 45 species in 20 families have been recorded. Eight species are new Hong Kong records including two newly established exotic species. Five of the eight species have not been recorded in Guangdong Province (see Table 1). Brackish water species and marine vagrants were excluded from this survey.

Table I New records of freshwater fishes for Hong Kong

Species Remarks
Noemacheilus incertus  
Awaous melanocephalus Not recorded in Guangdong
Ctenogobius cervicosquamus Not recorded in Guangdong
Stiphodon sp. Await identification, not recorded in Guangdong
Channa gachua  
Mastacembelus armatus  
Poecilia sphenops Exotic species, not recorded in Guangdong
Tilapia zillii Exotic species, not recorded in Guangdong

While new records of freshwater fishes are still being made locally, there is no room for complacency. The overall prospect for fauna and flora associated with lowland streams looks extremely bleak indeed; the rate of channelization, a by-product of rural development, has never been higher. It is particularly disturbing because the engineering designs of flood channels in Hong Kong have rarely if ever considered the ecological consequences of replacing a natural stream by a homogeneous concrete ditch. Also the Government's efforts at pollution control are far from satisfactory (go to Ho Pui at Kam Tin and Ping Yuen River above Sheung Shui if you don't believe me!). Other lowland streams which still support good fish populations are being regularly electrofished, a fishing method well known to greatly deplete fish populations and alter composition. Dudgeon (1993) listed 11 native freshwater fishes as threatened with extinction or possibly locally extinct already; only 4 species listed were recorded during the present survey (Rasbora steineri, Acrossocheilus wenchowensis beijiangensis, Rhodeus sp., and Oryzias latipes). Sadly, all were found in and around development sites. In addition, five of the recently recorded species were found in only one location. Considering the rate of urbanization and the alarming appetite for channelization shown by our government, these five fish could be considered as threatened with extinction in Hong Kong. All are freshwater or amphidromous species mainly confined to lowland watercourses (see below).

List of freshwater fish threatened with local extinction in Hong Kong (based on Dudgeon (1993), and the present survey conducted by the author).
*=Species recorded during the present survey

Plecoglossus altivilis
Rasbora steineri*
Tanichthys albonubes
Aphyocypris lini
Rasborinus formosae
sp. * (see Note below)
Acanthorhodeus macropterus
Acrossocheilus wenchowensis beijiangensis*
Pseudorasbora parva
Cobitis sinensis
Oryzias Iatipes*
Awaous meIanocephalus*
Ctenogobius cervicosquamus*
Stiphodon sp*
Channa asiatica*
Channa gachua*
Macropodus concolor
Mastacembelus armatus

The study is still in its early stages. However, the urgent need for the protection of native freshwater fish is already obvious; half of the 45 species recorded so far were found in only one or two sites, none of the sites visited are protected and many are being destroyed for development. Furthermore, no lowland freshwater waterways are protected in Hong Kong. With many of the rural villages being re-developed, and pending projects to develop north Lantau and a new 8-lane highway between Shatin and Sha Tau Kok, the freshwater fishes, together with other wildlife living in and along the lowland rivers, are highly susceptible to local extinction. Any loss of fish species due to careless development is likely to be permanent and they will never be naturally restored by colonization from populations elsewhere. It is hoped that this study can race against time to help government decision-makers to evaluate the environmental impacts of developments around lowland streams. My ultimate intention in writing this article, however, is to draw some much-needed attention to the protection of native freshwater fishes, many of which depend entirely on lowland waterways. These lowland streams/rivers, together with the adjacent marshes, are probably the most threatened wildlife habitats in Hong Kong at present.

Six years have elapsed since Dudgeon (1993) warned us about our fast-disappearing native freshwater fish and urged us to protect them. Regrettably, ABSOLUTELY NOTHING has been done (or even attempted?!) in regard to this matter. Are freshwater fishes really that worthless? Does anybody care?

Note: The bitterling (Rhodeus sp.) that occurs in Kam Tin stream, was discovered and identified as Rosy Bitterling (Rhodeus ocellatus) by Mr. K. W. Cheung of AFD in Porcupine! 18. However, specimens collected during the present study from the same site fitted the description of Rhodeus sinensis (Chinese Bitterling) rather than R. ocellatus. The body depth : body length ratio and colour in alcohol of the specimens are of particular diagnostic value in distinguishing this species from R. ocellatus. See Ye (1990) and Akai & Arai (1998) for detailed descriptions of the identification for the subfamily Acheilognathinae, especially the genus Rhodeus.

Akai, Y. and Arai, R. (1998). Rhodeus sinensis, a senior synonym of R lighti and R. uyekii (Acheilognathinae, Cyprinidae). Ichthyological Research 45 (1): 105-110.
Cheung, K.W. (1 998). Sightings of three freshwater fish. Porcupine! 18: 9.
Dudgeon, D. (1993). Hong Kong's vanishing freshwater fishes. Porcupine! 4:1 & 6.
Ye, F. L. (1990). The Acheilognathinae. In The Freshwater Fishes of Guangdong Province, pp.123-136. Ed. J. H. Pan. Guangdong, China: Guangdong Science and Technology Press. (In Chinese)

A little message

I have been contemplating organizing a freshwater group, believing such a group may be useful for the exchange of relevant information and discussion of issues of concern about Hong Kong's freshwaters amongst interested people. Any suggestions to, or anybody interested in this idea please contact Bosco Chan via email: or mobile: 96399240.

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More about Hong Kong freshwater fishes

by David Dudgeon

In the last three issues of Porcupine! there have been reports of sightings of new and/or rare freshwater fishes by K.W. Cheung and Keith Wilson et al. Their records update those published by Chong Dee-hwa and myself in 1993. There are a couple of matters arising from K.W. Cheung's two articles which I would like to address. The record of Rhodeus ocellatus (the bitterling) from a stream near Kam Tin reported in Porcupine! No.18 is exciting: I had guessed that these fish were extinct in Hong Kong [but see preceding article]. The bad news is that this stream is now polluted with silt arising from work on the new KCRC extension. Excessive sedimentation is known to degrade stream habitats in Hong Kong and elsewhere (e.g. Dudgeon, 1994), but the not-so-bad news is that KCRC have promised to install a silt trap in an attempt to correct the situation as soon as possible.

Rhodeus ocellatus (and related species in the same genus) has the unusual symbiotic habit of laying its eggs inside the body of another animal: the swan mussel, Anodonta woodiana. The eggs develop inside the respiratory chamber of the mussel and, in due course, hatch into tiny fish which escape to take up a free-living existence (see Dudgeon, 1985). Interestingly, during the initial stages of their lives, the larvae of the swan mussels (called glochidia) are parasitic on fishes, although the species identity of the host fish does not seem to be critical for Anodonta woodiana glochidia (Dudgeon & Morton, 1984). The bitterling cannot breed if the mussels are not present. K.W. Cheung did not report finding any mussels in the stream when he visited, but Bosco Chan and myself uncovered some during a recent visit. This stream is the only place in Hong Kong where we know that the fish and their mussel hosts co-occur in this symbiosis. Anodonta woodiana is reported from only one other site in Hong Kong (Plover Cove Reservoir: see Dudgeon & Morton, 1983). Unfortunately, swan mussels are highly sensitive to siltation and other environmental changes. Indeed, on a global basis, this family (the Unionidae) has an exceptionally large number of endangered species (World Conservation Monitoring Centre, 1996).

Back to K.W. Cheung's records. In Porcupine! No. 17 he reports a 'new' Eleotris sp. (Eleotrididae) from a waterlogged field in Sai Kung. Eleofris spp. spend most of their lives in freshwater but swim down streams into estuaries in order to breed. The larvae of these fish are planktonic so the marine phase of their life cycle is essential. It is therefore surprising and interesting to come across a juvenile in a marshy area. Presumably, this fish became lost while migrating upstream. Incidentally, I doubt this juvenile represents a new record for Hong Kong. Several Eleotrididae are known from the Territory and different species in the genus Eleotris are very difficult to identify when small. I suspect that this is a juvenile of one of the species already reported by Chong & Dudgeon (1992).

In the same article, K.W. Cheung makes the important comment that some of the fishes mentioned by Chong & Dudgeon (1992) are more widespread that previously thought. He mentions Yaoshanicus arcus as an example. This gives me the opportunity to make two points: firstly, the name Yaoshanicus arcus given by Chong & Dudgeon (1992) is probably incorrect; the species concerned is almost certainly Nicholsicypris normalis [see following article]. Secondly, the 'under-reporting' of fish reflects the fact that the Chong & Dudgeon (op. Cit.) paper included only the records we had to hand which were based on our rather unrepresentative series of collections; we did not survey every single stream in the Territory. A systematic survey of stream fishes in Hong Kong is now ongoing. That part of the survey dealing with lowland streams is being undertaken by Bosco Chan and, later in the year, I will be hiring a research assistant to work on sites that Bosco or I have yet to sample. The survey will be completed by the end of 1999. Initial work by Bosco Chan (reported separately in this issue of Porcupine!) has revealed a host of new records and interesting findings (including one I did not believe until I saw it with my own eyes!). Certainly, K.W. Cheung is right to say that caution should be exercised in assessing the ecological value of sites for fishes, and (to round things up neatly) it appears that the presence of bitterlings was not mentioned in the EIA report prepared for the KCRC extension.


Chong, D.-h. & Dudgeon, D., (1992): Hong Kong fishes: an annotated checklist with remarks on conservation status. Memoirs of the Hong Kong Natural History Society 19: 79-112.

Dudgeon, D. (1985) Anodonta woodiana (Bivalvia: Unionacea): the egg repository of Rhodeus sinensis (Pisces: Cyprinidae). - Malacological Review 18: 110.

Dudgeon, D. (1994): Functional assessment of the effects of increased sediment loads resulting from riparian-zone modification in a Hong Kong stream. – Verhandlungen Internationale Vereinigung für theoretische und angewandte Limnologie 25:1790-1792.

Dudgeon. D. & Morton, B. (1983): The population dynamics and sexual strategy of Anodonta woodiana (Bivalvia: Unionacea) in Plover Cove Reservoir, Hong Kong - Journal of zoology, London 201:161-183.

Dudgeon, D. & Morton, B. (1984) Site selection and attachment duration of Anodonta woodiana (Bivalvia: Unionacea) glochidia on fish hosts. - Journal of Zoologv, London 204: 355-362.

World Conservation Monitoring Centre, 1996. 1996 IUCN Red List of Threatened Animals. Gland Switzerland & Cambridge, U.K.: World Conservation Monitoring Centre: 228 pp.

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Yaoshanicus no more, but Nicholsicypris galore!

The long-time taxonomic confusion over a native cyprinid has finally been solved, thanks to the expert help of Dr. Sadovy at HKU. This handsome freshwater fish, previously identified as Yaoshanicus arcus (with three rows of lower pharyngeal teeth) is actually the superficially identical Nicholsicypris normalis (with two rows of lower pharyngeal teeth).

Nicholsicypris normalis is widespread in Guangdong, southern Guangxi and Hainan, while Yaoshanicus arcus is endemic to the Yaoshan area in Ouangxi. In Hong Kong, the fish has only previously been found in the Sai Kung area and Sha Lo Tung. Recently it was found to be quite common in two locations near Sha Tau Kok in the northeast New Territories, and a stream on northern Lantau. The Lantau record represents a rather dramatic local range extension, being the first record from the western side of the Territory.


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Even more about Hong Kong freshwater fishes

Previous records of Hong Kong's freshwater fish have included Plecoglossus altivelis, Rasborinus formosae, Tanichthys albonubes and Aphyocypris lini, referring to them as endangered or possibly extinct. Plecoglossus altivelis has been reported from Tai Ho Stream on North Lantau and may still survive there. There is a chance that this stream may soon be designated as an SSSI. The other three species are almost certainly extinct locally, and I have doubts that T. albonubes - a popular aquarium fish that is common in trade - was ever present in the wild. (I would be very pleased if someone could contradict me on this.) According to the China Red Data Book of Endangered Animals: Pisces published in 1998, T. albonubes and A. lini are extinct in the wild in China; R. formosae and P. altivelis is listed as 'vulnerable'. The authors of the Red Data Book suggest that attention needs to be paid to habitat protection including maintenance of channels to allow spawning migrations by anadromous P. altivelis fish.

A surprising entry in the Red Data Book is the listing of Parazacco spilurus as 'vulnerable'. This minnow is widespread and abundant in Hong Kong hillstreams but has a limited distribution elsewhere in China where it seems to be decilning. Perhaps Hong Kong fishes could provide broodstock for reintroduction into China once habitat protection can be ensured. To extend this suggestion further, I would like to explore the possibility of reintroducing T. albonubes to sites in Hong Kong where it used to occur - if I can obtain unequivocal evidence of an original presence. So …… any ideas?


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