Diversity and distribution of fish fauna of upstream and downstream areas at Koto Panjang Reservoir, Riau Province, Indonesia

Background: The capture fishery sectors in the river and reservoir play an important role in the Indonesian economy through increased income and diversification of livelihoods. The present study was conducted to ascertain fish diversity and their distribution pattern in the upstream and downstream areas of Koto Panjang Reservoir, Riau Province-Indonesia. Methods: Fish samples were collected for a period of 12 months using a variety of fish nets at four sites; Koto Mesjid (KM) and Batu Bersurat (BB), located in the upstream area of Koto Panjang Reservoir and Rantau Berangin (RB) and Kuok (KK), located in the downstream area of Koto Panjang Reservoir. Data obtained were analyzed using standard taxonomic keys based on morphometric characters. Results: A total of 44 species belonging 19 families and 33 genera were recorded in the study area. Alpha diversity indices showed that fish diversity in this area was quite high (Shannon’s index = 2.10 and Simpson-D = 0.21) and evenness was low (evenness H/S =0.19). The ﬁsh in KM and BB sites (upstream) were from eight and 11 families, respectively. In RB and KK sites (downstream), fish were from 16 and 15 families, respectively. In KM, BB, RB and KK sites, the dominant family was Cyprinidae, comprising 33.45%, 50.95%, 43.04% and 39.35% of all fish caught at each site, respectively. Exotic species, especially Nile tilapia, were 20.15%, 14.11%, 5.62%, and 5.34%, respectively. Some differences were also noted between the upstream and downstream reservoirs, with a slight increase in exotic species in the upstream reservoir over the study period (from 11.39% vs. 34.66%), corresponding to decrease of native species (from 88.61% vs. 65.34%). Conclusion s: The diversity and distribution of fish fauna were varied in upstream and downstream areas of Koto Panjang Reservoir. The exotic species were found to be dominant in the upstream reservoir areas.


Introduction
The capture fishery and aquaculture sectors play an important role in the Indonesian economy through increased income, diversification of livelihoods, supply of animal protein, and foreign exchange earnings. In 2018, the total fishery production of Indonesia was 23.186,442 metric tons, of which 467,821 metric tons was obtained from inland capture fisheries, 6,603,631 metric tons was obtained from marine fisheries, and 16,114,991 metric tons was obtained from aquaculture fisheries production 1 . A total of 1,300 fish, including 40 endemic species are known to inhabit in the freshwaters of Indonesia, with 16 exotic species recorded in Indonesia 2 . The production from the inland capture fisheries of Indonesia comes from wetlands (rivers, lakes, swamps, oxbow lakes, floodplains, etc). In Riau Province, one of the rivers that produce freshwater fish from capture fishery is the Kampar Kanan river. Fithra and Siregar 3 found 54 species in Kampar Kanan River, while Aryani 4 reported 40 species. At present, major Cyprinidae species such as Leptobarbus hoevenii, Osteochilus haselti and Rasbora argyrotaenia, along with exotic species, such as common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus), are the available species of fish at local food markets.
According to Mulyadi 5 , Kampar Kanan river is one of the largest rivers in Riau Province. It is approximately 213.5 km long and between 125 to 143 m wide, with significant capture fishery potential. Since 1996, this river has been dammed into a reservoir (Koto Panjang Reservoir) for the operation of a 114 MW hydroelectric power plant. The dam height is 96 m and located at altitude of 85 m above sea level 5 , and at the geographical position 0°17'23.76˝N and 100°52'53.39˝E. However, at the location of the dam, there is no fishway. The abiotic and biotic characteristics of river ecosystems can be affected by the construction of dams. These conditions have an impact on mortality and failure of fish migration [6][7][8][9] . The hydrologic regime of streams changing from lotic to lentic can influence the water retention in the reservoir. In general, the lentic condition causes a decrease in native species and then an increase in exotic species 10,11 . Furthermore, the degradation of aquatic fauna habitats can be caused by an increase in homogeneity of water channels, which has an effect on the seasonal flow variability of river 12 . The reduction in river runoff also affects the habitat and distribution of fish fauna.
On the other hand, there are serious threats to the original fish biodiversity in the downstream and upstream regions of the reservoir due to the dam of the hydroelectric power plant, such as sand mining in river, land use change and aquaculture activity with cages, which can affect the depth of river water, food availability, and breeding sites. Amadi et al. 13 state that original biodiversity can be eroded by habitat degradation and alien species impact. Meanwhile, aquaculture heavily impacts the structure and diversity of local fish communities 14,15 . Hence, it was essential to study fish diversity continuously in different ecosystem areas, including upstream and downstream areas at Koto Panjang Reservoir, Riau Province, Indonesia. Specimens of fish species categorized as non-endangered and exotic were killed once caught. Endangered fish species (Hemibagrus wyckii) were returned to the river in good condition following analysis in the field. All efforts were made to ameliorate any animal suffering through anaesthetizing fish with ice water before euthanization.

Ethical statement
Sampling sites and methods of specimen collection Fish sampling was carried out from January to December 2018 at four sites, namely, Koto Mesjid (KM) and Batu Bersurat (BB) (upstream reservoir), Rantau Berangin (RB) and Kuok (KK) (downstream reservoir) ( Table 1). Fish samples were randomly collected from the study area using traditional fishing gear (e.g. traps nets, cast nets, gill nets, drag nets, and fishing poles). Data was collected once a month at each site and five pieces of fishing gear were in operation at any one time. Trap nets (local name bubu) are made from bamboo woven with rattan and have a cylindrical front with a diameter of 80 cm and cone-shaped back, with a length of two meters. Chicken intestine was placed inside the gear as bait. This gear was used between the hours of 18:00 and 06:00 at the bottom of river and reservoir to catch demersal fish such as Bagridae, Pangasidae, Gobitidae, Claridae, Anabantidae, Belontiidae.
Cast nets (local name Jala) are a type of active fishing gear made from string, with a length of 2.5 meters and mesh size of 1.5 inches. This gear was used on the river and reservoir sides by fishermen using canoes. This gear was operated during the day from 06.00 until 10.00. The purpose of cast nets is to catch the family of Cyprinidae, Osphronemidae, Notopteridae and Cichlidae.
Gill nets (local name jaring insang) are made of rectangular monofilament yarn, are 60 meters in length and 8 meters in depth, with a 2.5 inch mesh size. These were operated passively and transversely on the surface of river from 18.00 until 06.00 to catch pelagic fish such as Cyprinidae, Osphronemidae, Notopteridae and Cichlidae.
A drag net (local name belad) is a passive fishing device made from nylon net material with a diameter of 0.15 mm and a mesh size of 0.5 inches. This gear is assisted by bamboo or wood as a cantilever, with a height of 2.5 meters and a length of 100 meters, which was placed parallel to the river coastline from 18.00 until 06.00. The purpose of the drag net is to catch the family of Bagridae, Pangasidae, Gobitidae, Claridae, Anabantidae, Belontiidae and Siluridae.
The fishing pole (local name rawai) used consisted of a main line with a length of 50 to 100 cm and a distance from one branch line to another of 1.5 meters. One fishing pole has hooks ranging from 20 to 30 pieces and the hooks are size no. 15. The fishing pole was operated passively on the river bottom between the hours of 18.00 and 06.00 and used chicken intestine as bait. The main purpose of fishing pole is to catch the family of Bagridae, Tetradontidae, Pangasidae and Channidae.
Samples were classified as endangered, non-endangered and exotic fish species based on the categories described by Kottelat and Whitten 16 . Once caught, fish were anaesthetized in ice water at a temperature of 5°C. Euthanization was achieved by piercing part of the brain of the fish. Samples were given an intraperitoneal injection prior to store in a formalin solution. Smaller specimens were stored directly in 5% formalin solution, while the larger specimens were stored in 10% formalin solution. Specimens that were categorized as non-endangered were transported in a cold box (10 °C) to the Fish Biology and Ichthyology Laboratory, Department of the Aquaculture, Riau University for measurement of specimen length, weight, and morphometric characteristics. Endangered fish species such as Hemibagrus wyckii were analyzed and measured in the field. Then, the same fish was returned to the river in good condition. The length, body weight and morphometric characteristics were only collected for 10 individual specimens from each species.
Samples from each site were separately packed in labeled plastics jars according to date, site, time, and locality. Each specimen was labeled with a specific number manually. Classification and taxonomic identification of the sampled specimens was completed using standard keys 17,18 on the basis of morphometric and meristic characters.

Data analysis
The data of different species for abundance and occurrence was calculated for species richness (S), Shannon diversity Index (H'), Simpson diversity index (D), evenness (H/S) and Sorenson's coefficient (CC) [19][20][21] using Microsoft Excel 2010 (version 14.0). The accuracy of the data and results were verified by applying all the diversity indices separately according to sampling months and sampling sites.

Monthly occurrence of fish fauna in the upstream and downstream areas at Koto Panjang Reservoir
During the study, forty-four different species of fish were collected from the study area. A total of 8017 specimens of fish were collected from four sites 20 . The details of the fish species collected on a monthly basis for the period of one year (January to December 2018) are presented in   ecosystems, including species richness and diversity indices, are influenced by the alterations in abiotic factors such as river water temperature and discharge [24][25][26][27] .
Our study also revealed significantly lower species diversity in KM and BB (upstream reservoir) compared to that of RB and KK (downstream reservoir). The overall richness in KM was much lower than that found in RB (18 vs. 37). During the research period, we also recorded a slight increase in exotic species in the upstream reservoir and a decrease in native species. Therefore, the implication of exotic species such as Nile tilapia and common carp have negative effect to native species in the upstream area of Koto Panjang Reservoir. In contrast, in a Portuguese reservoir, it was found that there was a slight increase in exotic species in the downstream reservoir 6 . This result might be a consequence of cumulative impacts of cultivation of fish in floating net cages, such as Nile tilapia and common carp. According to Russel et al. 28 , Nile tilapia cause the extinction of native fish species by preying on eggs, fry and small fish of other species. On the other hand, the decrease in species richness can be influenced by aquaculture activity, such as water quality degradation, intensified competition, invasive species, and habitat fragmentation 14,[29][30][31] . Koto Panjang Reservoir was categorized as eutrophic, with level index values ranging from 4.6-5.2 32 . According to Edwards 33 , species with high environmental tolerance would be survive in poor environmental conditions, such as high pollution caused by food waste at the reservoir, while the sensitive species will disappear. Furthermore, fish populations in a reservoir can be affected by hydropower dams 5,6 . In addition, the intensifying competition for food and space between wild species and the large number of cultured species will lead to a decrease in wild fish numbers 34,35 .
Our study confirmed the existence of three species, Pangasius pangasius, Wallago leerii and Chitala hypselonotus, at Koto Panjang Reservoir that were not found previously by Warsa et al. 36 and Krismono et al. 37 . The study area also represents the area of the Kampar Kanan river with the largest fish species, including W. leerii, H. wyckii and P. pangasius. The construction of the dam for power generation purposes is posing serious threats to the biodiversity of Kampar Kanan river. After the construction of the Koto Panjang dam on Kampar

Discussion
Our results showed that the highest abundance and diversity of fish species collected in June, July and August, which may be due to a lesser water current in the study area during these dry season months. According to Kriaučiūnienė et al. 22 the abundance of fish species in rivers can be affected by river discharge. However, future alterations in river water temperature will have a significantly larger influence on the abundance of fish than river discharge. Overexploitation and illegal sand mining have affected the abundance of fish in the Kampar Kanan river 23 . Furthermore, the fundamental measures of aquatic  Kanan river, the movement of fish upstream has been restricted. Osteochilus kelabau has not been reported at RB in our study although this species has previously been found in this area 4  In addition to the species richness (S) analysis, Shannon diversity index (H'), Simpson diversity index (D) and evenness (H/S), we also analyzed the Sorenson's coefficient (CC) between the upstream and downstream sites. The Sorenson's coefficient for each site varied between 0.54 and 0.92. The highest value of Sorenson's coefficient was recorded between KM and RB, at 0.92, and the lowest value was recorded between BB and RB, at 0.54 (Table 5). According to Sorenson's coefficient, these communities have quite a bit of overlap or similarity.
The high diversity of native species in the water body will decrease their tolerance in poor aquatic environments. In contrast, the invasive fish species have a high tolerance to poor water quality 42 . The interaction between different species, combined with the limnological and physical properties of the aquatic ecosystem, may influence the diversity and distribution of fish fauna 43 . In this study, the diversity of fish to be found smaller than Fhitra and Siregar 3 , who reported 58 fish species belonging to 23 families and 40 genera from Kampar Kanan river. Simanjuntak et al. 44

Conclusion
The results indicate that the diversity and distribution of fish fauna in upstream and downstream areas of the Koto Panjang Reservoir were varied, and the evenness was low. The abundance and composition of fish in each site was dominated by Cyprinidae families, although exotic species were more dominant in the upstream reservoir compared to the downstream reservoir areas. Therefore, the management of the river and reservoir in a more holistic manner is important, for example, the management of land use, sand mining and aquaculture activity, as well as possible habitat restorations. All the factors above are a prerequisite for the environmental sustainability and conservation of fish diversity in the upstream and downstream areas at Koto Panjang reservoir and other regions. This project contains the following underlying data:

Data availability
-Tables 2 -5 (raw data for ichthyodiversity of fish in each site).
- Table 6 (data for abundance and composition of aquatic fauna each sites in the upstream and downstream areas at Koto Panjang Reservoir) - Table 7 (data for grand total and percentage of families of aquatic fauna in the upstream areas at Koto Panjang Reservoir) -

Open Peer Review
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