Tan Shan River, tributary of Ng Tung River, New Territories, Hong Kong

_th place in Biotope Aquarium Design Contest 2020

Volume:  160 L
Dimensions: 100x40x40 cm
List of fishes: Rhinogobius Duospilus
List of
Description of decorations: The decoration of this aquarium was acquired to resemble the natural biotope as close as possible without hurting it’s natural environment. (or any natural environment). The bottom layer of the aquarium consists of river sand with a grain size of 0.8mm, artificial river stones protrude from the sand. The appearance of the sand is affected by the water current and the fish burrowing, leaving a build up of sand around the stones giving it a natural feel.

Description of equipment: The aquarium is equipped with a large canister filter; the JBL CristalProfi e1501 greenline (1400l/h), and a streaming pump; the EHEIM streamON+ 3500 (with a maximum capacity of 3500l/h). The lighting is a EHEIM classic LED daylight (up to 6500K), powered by a EHEIM Dimmer Day & Night, the extendable mounting brackets on the lighting make it possible to place the lighting at angles which allows creating natural lighting effects.

Water parameters: The water is clear and well oxygenated due to the fast flowing current, it is alkaline with the pH having a value of 7.5 and the hardness has a value of 10 gH. The aquarium is kept at room temperature, so the temperature has an average range of 18°C to 24°C, regular water changes also cause temperature drops.

Additional info: Water changes are done every 14 days which consists of changing 25% water, the water comes straight from the tap resulting in small temperature drops, highly appreciated by the fish.


Description of the area surrounding the biotope:

Hok Tau and Lau Shui Heung Reservoirs, located in the upper course of Ng Tung River, were built in 1968, with the purpose of collecting and diverting water from nearby streams to Plover Cove Reservoir. Meanwhile, some river water is used to irrigate adjacent farmland. This section of the river, named as Tan Shan River, is one of the main tributaries of Ng Tung River. Tan Shan River is natural with excellent water quality, and it has been designated by the Agriculture, Fisheries and Conservation Department as an “Ecologically Important Stream”. The river supports a diversity of flora and fauna. Notably, it provides an important habitat for dragonflies. Ng Tung River is located in the northeast New Territories. The river catchment covers areas such as Lung Yeuk Tau, Fanling and Sheung Shui. Ng Tung River is a large tributary of the Shenzhen River System, and its own different tributaries bare different names, making the delineation of Ng Tung River Catchment complicated. The river named as Ng Tung River on map originates from the southern slope of Robin’s Nest summit (492 m) at an altitude of about 450 m, and flows westward to Fu Tei Au. However, the actual origin of the main stream of Ng Tung River is from the west of Wong Leng summit (639 m) at an altitude of about 580 m. The main stream flows down the valley on the western slope of Wong Leng and goes into Hok Tau Irrigation Reservoir through Ping Shan Chai. It then turns northward to Tan Chuk Hang, and then westward merging with the tributary that originates from Robin’s Nest at Ko Po North Tsuen. This river section from Wong Leng to Ko Po North Tsuen is called Tan Shan River on the map. The main stream of Ng Tung River merges with other major rivers in the region as it flows along. A few hundred meters to the west of Ko Po North Tsuen, the main stream merges with a tributary named Kwan Tei River. The main stream continues westward and passes north of Lung Yeuk Tau before merging with a tributary named Ma Wat River. The main stream then passes northern Sheung Shui, and merges with two tributaries named Shek Sheung River and Sheung Yue River near Fu Tei Au. Finally, the main stream turns north and merges with Shenzhen River.

Description of the underwater landscape of the biotope:

The landscape of Hong Kong is dominated by hills and ravines and flat land is restricted to the low floodplains and coastal regions. In this hilly domain, hundreds of small rocky streams flow through steep ravines. These hill streams are typically fast flowing at their upland sources, and gradually reduce speed as they wind along hill cuttings to reach the lowlands. There are only a few long and meandering rivers in Hong Kong and are found only in the floodplains of the northern and northwestern NewTerritories. There are over 2 500 km of natural streams and rivers in Hong Kong, mostly located in hillsides remote from developed areas. Many of these natural streams and rivers are good habitats supporting a variety of wildlife. They have important ecological functions and carry high aesthetic and landscape value. A natural stream or river refers to a natural channel with natural water fed from upper terrains, which covers both perennial stream and river with water flowing throughout the year as well as intermittent ones with water-flow only during the wet season. The streambed is natural and not manmade, which could consist of mixtures of bedrocks, boulders, cobbles, gravels, sand, silt or clay. The banks are also largely natural and defined, covered with bank-side and riparian vegetation.

Description of the parameters of the habitat: Rivers and streams in Hong Kong are generally short with small flows, many of which have their upstream sections located within the catchment areas of reservoirs where potable water is gathered. Other than for drinking water supply, the primary beneficial uses of the rivers and streams in Hong Kong include maintenance of aquatic life, as general amenity, flood prevention and storm water drainage. The main channel of Shing Mun River is the only watercourse used for secondary contact recreation activities. Tan Shan River is natural with excellent water quality, and it has been designated by the Agriculture, Fisheries and Conservation Department as an “Ecologically Important Stream”. The river supports a diversity of flora and fauna. Notably, it provides an important habitat for dragonflies. The Dissolved Oxygen (DO) has a minimum value of 4mg/L, a average of 6.0-8.9mg/L and a maximum value of 15mg/L, Dissolved Oxygen (DO) and E.coli are two important parameters indicating the general conditions of water and its health risk to the public. Dissolved Oxygen indicates the total amount of oxygen dissolved in the river and stream water. Most aquatic organisms need oxygen for respiration and maintenance of life. The pH ranges from 6.5 to 8.5  depending on the exact location and time of the year, the Ammonia-Nitrogen has a value that ranges from 0.032 to 0.480 mg/L and the Nitrate-Nitrogen ranges from 0.440 to 0.900mg/L. The water temperatures range from 18°C to 28.4°C depending on the season and weather conditions.

List of fishes and invertebrates occurring in the nature biotope: Anguilla japonica, Acrossocheilus parallens, Hypophthalmichthys nobilis, Barbus schwnenfeldi, Carassius auratus, Ctenopharyngodon idellus, Cyprinus carpio, Parazacco spilurus, Puntius semifasciolatus, Zacco platypus, Misgurnus anguillicaudatus, Liniparhomaloptera disparis, Pseudogastromyzon myersi, Pterocryptis anomala, Silurus asotus, Clarias fuscus, Clarias gariepinus, Gambusia affinis, Poecilia reticulata, Xiphophorus hellerii, Xiphophorus variatus, Monopterus albus, Oreochromis mossambicus, Oreochromis niloticus, Tilapia zillii, Rhinogobius duospilus, Rhinogobius giurinus, Anabas testudineus, Macropodus opercularis, Channa asiatica, Channa gachua, Channa maculata, Channa striata

List of plants found in the nature biotope: The vegetation around the Tan Shan River is limited to wetlands and riparian vegetation. Riparian vegetation provides food for many aquatic organisms in the stream as well as sheltering effect that is important for regulating the water temperature. Riparian vegetation also serves important functions including purifying water by removing sediments and contaminants; reducing the risk of flooding; and reducing erosion on stream bank.

Threats to the ecology:
Sources of information:

Book: “Dudgeon and Richard Corlett – Hills and Streams: An Ecology of Hong Kong”

Comments of the members of the jury of Biotope Aquarium Design Contest 2020