Fish community structure in Sermo Reservoir, Yogyakarta, Indonesia: Initial study on invasive fish species

Invasive species are becoming issues in freshwater ecosystems throughout the world including Indonesia. Sermo Reservoir is located in Yogyakarta, Centra Java, was indicated to have invasive species identified as Cichlidae family. The study aimed to assess fish communities’ structure and identified invasive fish in Sermo Reservoir. The research was conducted in Sermo Reservoirs, Yogyakarta, Indonesia on March-October 2019. In total, about 3,084 individuals of 10 fish species belonging to 3 families and 8 genera were captured using a experimental gillnets (mesh size 0.75; 1; 1.5; 2; 2.5; 3 inch) at five stations. The fish community in Sermo Reservoir was dominated by Cichlid fish (98.66%). Red devil (Amphilophus labiatus) and Midas cichlid (A. citrinellus) were dominant species founded in Sermo Reservoir (58.82% and 37.00%, respectively). Another species of cichlid that caught consist of nile tilapia (Oreochromis niloticus), mozambique tilapia (O. mossambicus), and jaguar cichlid (Parachromis managuensis). The study showed that Amphilophus spp. have high dispersal (One-way ANOSIM revealed Amphilophus spp. was not significantly different for spatio-temporal (p>0.05)). SIMPER analysis (p < 0.05) showed that A. citrinellus and A. labiatus had spread throughout the waters and were concentrated in Tegiri station which had more littoral zones.


Introduction
Reservoirs 'the man-made lakes' are constructed with the primary aim of the generation of electricity and water storage for purposes of irrigation as well as the water supply for humans. Moreover, reservoirs have an integral role in the fisheries and livelihood security of the local community. Sermo Reservoir, the only reservoir was built in Yogyakarta Special Region, an area of about 157 ha and volume capacity of about 25 million m 3 . The Sermo Reservoir was constructed in 1996, with the aim of water storage for irrigation and water drinking supply. Furthermore, Sermo Reservoir also provides benefits for the fisheries sector especially capture fisheries. The Sermo Reservoir has an important role in providing animal protein and generating employment for the surrounding community [1].
Small scale fisheries in Sermo Reservoir used to be very beneficial for the local people, however, the fisheries yield was reported to be declined due to the emergence of invasive species known as a red devil (Amphilophus spp.). Red devil fish was unintentionally introduced to Sermo Reservoir around 1995, through fishes restocking program in Sermo Reservoir [2]. The Red Devilfish in Sermo Reservoir currently has dominated in fishermen catch. Currently, that red devil dominated almost >70% of the catches [2][3][4]. In term of consumption, the red devil and midas cichlid has no economic value, and need more process to produce a useful product such as poultry feed [2].
The fishes found in the early inundation of Sermo Reservoir were silver barb (Barbonymus gonionotus), carp (Cyprinus carpio), spotted barb (Barbodes binotatus), Yellow rasbora (Rasbora lateristriata), Barred loach (Nemacheilus fasciatus), catfish (Clarias batrachus), nile tilapia (Oreochromis niloticus), Mozambique tilapia (Oreochromis mossambicus) and Guppy (Poeciliata reticulata) [5]. The fishes in Sermo were native species from the river and introduced species from the stocking program. Since early inundation until the 2000s, several government agencies have stocked some species in Sermo Reservoir to increase fishermen catch and production, such as nile tilapia and common carp. The red devil species is thought to have entered Sermo Reservoir through the stoking of tilapia since the red devil seed looks similar to the tilapia seed. The fish turned out to have a very high rate proliferation in Sermo Reservoir and dominate the fishermen catch [5,6].
The stocking of fish into inland water in Indonesia is mostly implemented in the lentic ecosystem (lake, reservoir, swamp, and other types of puddle) aimed to increase the production of fish biomass. The stocking of fish into inland water should be conducted with a precautionary approach to prevent changes in ecosystem balance. Introduced new species of fish into inland water can cause a negative impact if the species turn invasive and detrimental both ecologically and economically [2,7]. The presence of invasive alien species can threaten native species in the ecosystem, and contribute to the extinction of native fish up to 30% [8].
This study aimed to assess the fish community and identify invasive species in Sermo Reservoir. This information is expected to be used as basic information to determine policy in controlling or eliminating invasive species in Sermo Reservoir.
The fishes were caught then measured using a ruler with a precision of 1 mm for its total length and height, furthermore weighed using a digital scale with a precision of 0.01 grams. Identification of fish species refers to Barlow and Munsey [12], Kottelat et al. [13], Loiselle [14], and fishbase site [15]. Fish samples that required further identification were preserved using 10% formalin solution and put in the coded plastic sample.

Data analysis
Fish community was analyzed using an index of relative importance (IRI) that were combined abundance (N), biomass (W), and occurrence of catch (F) with formula IRI = [(%Wi+%Ni)Fi/ Σ[(%Wi+%Ni)Fi]*100 [16][17]. IRI of the fish community was calculated based on total catch spatial and temporal. Diversity index of Shannon or entropy (H'), equitability Pielou's index (J'), and Simpson index of dominance (D) were assessed for relative abundance from each fish species with bootstrap (center type; n=9,99) to get interval limits of 95% [18]. One-way Analysis of Similarity Test (ANOSIM) was used to assess spatial and temporal differences in abundance and biomass of fish communities. The similarity matrix used in the ANOSIM test was calculated based on Bray-Curtis [18]. SIMPER analysis (Similarity Percentage) was used for ANOSIM calculation which was significantly different (P<0.05) in spasio-temporal fish communities [19]. All the calculation process was done using PAST 3.26 [19].

Species composition
In total, the fishes were caught by approximately 2,089 individuals consisted of 10 fish species belonging to 8 genera and 3 families (table 1). The dominant family was Cichlidae that consisted of 5 species, midas cichlid (Amphilophus citrinellus), red devil (Amphilophus labiatus), mozambique tilapia (Oreochromis mossambicus), nile tilapia (Oreochromis niloticus), and jaguar guapote (Parachromis managuensis). All the species of Cichlidae family in Sermo were identified as non-native species. The most abundance of cichlid species was Amphilopus labiatus, followed by another cichlid, Amphilophus citrinellus. Based on the index of relative importance (IRI), Red devil and Midas had higher value than other species, mewhich ans both of species dominated catches during the survey. Cichlid fishes were more abundant compared to native species (98.66%).
The Midas cichlid complex (A. citrinellus, A. amarillo, and A. labiatus) existence in Indonesia was still being debated especially for their species identity. Several publications referred to the "red devil" fish, the local name of Amphilophus spp. used in Sermo Reservoir, as A. citrinellus [20]. Nevertheless, other publications refer to A. labiatus [3,4] and A. amarillo [21]. An effort to investigate the red devil fish through a molecular approach by using a partial control region of mitochondrial DNA. It was concluded by the author that the red devil fish was identified as A. amarillo [21]. Nevertheless, the study provides weak evidence and shows no distinct clade was successfully constructed from the bootstrapped phylogenetic analysis. The uses of mitochondrial regions were also proved to be unsuitable for Midas cichlid complex identification in their original location (Lake Nicaragua) [22]. Until now, the only powerful approach to distinguish the Midas cichlid was based on their phenotypic or morphological information [23]. It was identified that A. amarillo has a specialized phenotypic characteristic by looking at the orange coloration of the throat area [24]. Thus, the closest species existing in Indonesia were either A. citrinellus or A. labiatus. Our previous investigation has successfully identified through Generalized Proscrusted Analysis (GPA) morphological, the differentiation between A. citrinellus and A. labiatus  2). This finding was also confirmable as their similar morphology differences from A. citrinellus and A. labiatus from Nicaragua ( figure 3). The existence of these two species is similar to Kedungombo Reservoir [25].   [26] and their origin location, Nicaragua Lake (bottom figure) [23]. Native species of fishes in Sermo were spotted barb (Barbodes binotatus), silver barb (Barbonymus gonionotus), bonylip barb (Osteochilus vittatus), and yellow rasbora (Rasbora lateristriata) while other fishes were introduced species. All the native species in Sermo belong to Cyprinidae and the introduced species are Cichlidae and Eleotridae. IRI values that were presented in table 1 show that Cichlidae species which were Amphilophus labiatus and Amphilophus citrinellus more abundant than other species in Sermo Reservoir. All the native species of fishes (Cyprinidae) in Sermo were found in smaller abundance compared to Cichlidae species that were non-native species. Based on the IRI value (table  1), silver barb (Barbonymus gonionotus) was the species that has the smallest IRI value. This is because the species was just re-stocking along with bony lipbar (Osteochilus vittatus) in June 2020 by the Fish Quarantine and Inspection Agency of Yogyakarta (Ministry of Marine Affairs and Fisheries). Based on the analysis, Cichlidae species, especially Amphilophus labiatus and Amphilophus citrinellus were being invasive species that dominated in fish community structure.
The invasive of Cichlidae in the freshwater ecosystem not only occurred in Sermo Reservoir, it was reported that a similar case also occurred in another freshwater ecosystem in Indonesia. The Cichlidae fish that enter inland water and become invasive in Indonesia, mostly because of unintentional introduction, such as occurred in Ir. H. Djuanda reservoir [28], Cirata reservoir [29], Jati Gede reservoir [30], Kedungombo reservoir [25], Lake Matano [31,32], Beratan Lake [33] and Sentani Lake [34,35]. A similar condition also occurred in Sermo Reservoir whereas the Cichlidae species have high proliferation and become dominant in the community.

Spatially and temporally fish composition
Observation of the fish community in Sermo Reservoir spatially showed that Amphilophus labiatus and Amphilophus citrinelus were found in high abundance across all the sites compare to other species. IRI value of fish community structure spatially in Sermo Reservoir in table 2 shown that Amphilophus labiatus were recorded found abundant in all site, and Amphilophus citrinelus, though distributed across the sites, it found most abundant in DAM site. It seems that Amphilophus labiatus has invaded almost all part of the reservoir so that Amphilophus citrinelus were concentrated in the DAM area (table 2). This rapid expansion of red devil cichlids can be explained by the morphology of cichlids. The Cichids have a highly integrated pharyngeal jaw apparatus, which supports them during the invasion and colonization of new lacustrine environments [36]. The invading cichlids can successfully occupy a range of adaptive zones and to specialize progressively into diversified subzones, which may help to explain why cichlid fishes have successfully invaded new ecosystems in many different parts of the world [37].  The ecological indices consist of diversity index (H'), equitability Pielou's index (J'), and Simpson index of dominance (D) of fish community structure spatially and temporally in Sermo is presented in figure 4. The diversity index spatially and temporally was categorized as low-medium, while the dominance index and equitability were medium ( figure 4). This indicated that one species tend to be dominant in the community with the result that diversity species becomes low and dominance rise. In Tegiri site, the diversity index was categorized as low and dominance index was high. This indicated that the Amphilophus spp. was abundant in Tegiri. The diversity index value that was assessed temporally showed that the ecological index tends to improve in June when the silver-barb restocking was implemented. Amphilophus spp. has dominated the fish community structure in Sermo Reservoir and affected the fish community ecologically.
Oneway ANOSIM revealed fish community abundance was not significantly different for spatial (R=0.0417, p>0.05) and temporal (R=0.0285, p>0.05) as presented in tables 3 and 4. This is because Amphilophus spp. has dominated completely with the high abundance in all part of Sermo Reservoir.    Figure 5. Bray-curtis similarity dendrogram of fish community in Sermo Reservoir (remarks: Midas = midas cichlid; Jaguar = jaguar guapote; Rasbora = yellow rasbora; Marble = marble goby; Mozam = mozambique tilapia; Silver = silver barb; Bonylip = bonylip barb; Nile = nile tilapia; Spotted = spotted barb). Based on bray-curtis analysis (50% of similarity) there was six groups of the fish community ( figure  5). Group 1 consists of spotted barb, nile tilapia, and bonylip barb. Group 2 only has silver bar, while group 3 consists of mozambique tilapia and marble goby. Group 4 and 5 consists of yellow rasbora and jaguar guapote, respectively. The las group, consists of red devil and midas cichlid. Red Devil and midas cichlid share 79.08%, which means that the dispersals of both species are the same.

Conclusion
Amphilophus citrinellus and A. labiatus has dominated Sermo Reservoir spatially and temporally, therefore their existence in Sermo has altered the structure of the fish community. A. citrinellus and A. labiatus have the same dispersal pattern in Sermo, especially in the littoral zone.