Two new freshwater fish for Hong Kong
Specimens of freshwater fish were collected by our Field Officer Darwin Cheung during surveys of freshwater wetlands in the Sai Kung peninsula in the summer of 1997. Two species were found to be new records for Hong Kong.
Bagridae: Pseudobagrus trilineatus
One adult (length 7 cm; height 2 cm) and one juvenile (length 3 cm; height 0.5 cm) were caught in a pond in eastern Sai Kung. The pond was overgrown with the hydrophytes Ludwigia adscendens and Eichhornia crassipes. A site visit in winter found that the pond was drying up but the bottom was still wet and muddy.
Pseudobagrus trilineatus is a brownish fish with a smooth body and 4 pairs of barbels. The adult specimen has a bulky body and a large depressed head. The species can be easily identified by its three distinct yellow stripes along the trunk with the middle one, along the lateral line, being broken. The specimens also have a yellow C-shaped stripe at the 'neck'.
P. trilineatus is endemic to Guangdong and has previously only been recorded in streams of the Dongjiang (East River) catchment (Pan, 1990). The present discovery represents a first record of the species and the Family Bagridae in Hong Kong, and indicates that this species can also survive in pond habitats.
Eleotridae: Eleotris species (?)
A juvenile specimen (length 4 cm) was caught in an abandoned agricultural field near an estuary in west Sai Kung. The field was waterlogged with a thick layer of mud at the bottom, and was overgrown with grasses. The Black Paradise Fish (Macropodus concolor) was also found in similar habitats in the area.
The fish has a roughly fusiform body with a slightly depressed head. It has two separated dorsal fins with the second one being larger. The anal fin resembles the second dorsal fin in size and position. The pectoral fins are rather large and the pelvic fins are close to each other but not joined. The fins and other features indicate the fish is a member of the Eleotridae. However, it is not possible to identify the fish accurately as there is only one juvenile specimen. It is tentatively being identified as an Eleotris species.
The fish has a distinct colour pattern: it is brownish in colour with numerous small black dots laterally which make the fish look dark-coloured. However, the fish can turn paler when placed in a different environment. The dorsal surface of the body is paler in colour and has a pale brown stripe at the back. Such a colour pattern is not found in the members of the Eleotridae recorded in Hong Kong (Chong & Dudgeon, 1992) or Guangdong (Pan, 1990). It is not certain whether the colour pattern is simply a juvenile character. The identity of the species can only be determined when adult specimens are available. However, it is highly likely that the species is a new record for Hong Kong.
The number of freshwater fish species recorded in Hong Kong is increasing due to fish introductions (e.g. Wilson et al. 1997, Chong & Dudgeon, 1992), and there may be more new discoveries when further studies of freshwater habitats are carried out. Moreover, our understanding of the distribution and abundance of Hong Kong freshwater fish will be increased by such studies. For example, our surveys also found that Yaoshanicus arcus is more widespread than previously thought. The fish is rather common in freshwater habitats in Sai Kung.
Studies of freshwater habitats often focus on sites which are easily accessible (e.g. near to roads or paths), or look "good" (e.g. a clean stream with riffles and pools). Sites which are inconspicuous, difficult to access or do not look "good" are often neglected (a common phenomenon in the field surveys of EIA studies). It is possible that some interesting species may dwell in such sites. The discovery of Pseudobagrus trilineatus in this case is an example. On the other hand, some "good" looking sites may not necessarily have a diverse community or rare species. Caution should be exercised in assessing the ecological value (no matter whether high or low) of a site without a detailed field investigation.
I would like to thank my colleagues Mr. Simon Chan, Mr. Darwin Cheung and Dr. P.M. So for allowing me to examine the fish specimens and providing useful information.
Agriculture and Fisheries Department
Chong, D.H. & D. Dudgeon (1992). Hong Kong stream fishes: an annotated checklist with remarks on conservation status. Mem. H K Nat. Hist. Soc. 19: 79-112
Pan, J.H. (ed.) (1990). The Freshwater Fishes of Guangdong Province. Guangdong Science and Technology Press, Guangdong, China, p.589.
Wilson, K.D.P., S.Y.H. Lai and T.D Dahmer (1997). Fish introductions to Hong Kong: two recent case studies. Porcupine! 16: 9-11.
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