Ichthyofauna of Merbau River, Leuser Ecosystem Area, Indonesia: species composition, diversity, biometric condition, potency, and conservation status

Abstract

The Leuser Ecosystem Area (LEA) is one of the largest conservation areas in Southeast Asia. However, the explorations of ichthyofauna at LEA are still relatively scarce compared to other vertebrates fauna. We report the first ichthyofauna studies of the northern river of LEA in Aceh Province. This study aimed to determine the composition, diversity, biometric condition, potency, and conservation status of freshwater fish in Merbau River, LEA, Indonesia. Fish sampling was carried out at six research stations using selective gill nets, throwing net, hook, tray net, and scoop net. A total of 434 individual fish belonging to 21 species, nine families and six orders were collected from the sampling location. Cyprinidae was the predominant family obtained, namely 42.9%. Based on their conservation status, 85.7% of collected fish were categorized as Least Concern, 9.5% as Data Deficient, and 4.8% as Near Threatened. A total of 14 fish have the potential as consumption fish, two species have the potential as ornamental fish, and five others have the potential both as consumption and ornamental fish. All fish species collected had negative allometric growth patterns with growth coefficient values (b) ranging from 1.17–2.51. The diversity and evenness index of fish was categorized as moderate (H’ = 2.52) with stable conditions (E = 0.85).

Keywords:

• Freshwater fishes
• diversity indices
• growth pattern
• potency
• conservation area

1. Introduction

The Leuser Ecosystem Area (LEA) is one of the largest conservation areas (reaches 2.6 million ha) in Southeast Asia, comprising with high biodiversity of both flora and fauna (Nuribadah 2022). The composition of flora in LEA was recorded at 4000 species, where around 113 species were categorized as endemic (Ardi et al. 2021). Meanwhile, 739 species of fauna were also reported, including mammals, aves, reptiles, amphibians, fish, and other invertebrates (Djufri 2015). In addition, LEA has become the last natural habitat for endemic Sumatran fauna, for instance, orangutan sumatera (Pongo abelii), Sumatran elephant (Elephas maximus sumatrensis), Sumatran tiger (Panthera tigris sumatrae), and Sumatran rhinoceros (Dicerorhinus sumatrensis) (Djufri 2015). Unfortunately, the explorations of ichthyofauna in LEA are still relatively scarce compared to other vertebrates fauna.

An inventory of ichthyofauna is crucial for demonstrating variety, investigating imported and invasive fish, assessing the potential of fish, and contributing to the search for new species. Therefore, this information provided a valuable reference for constructing conservation policies for aquatic ecosystems (Shen et al. 2019; Mariac et al. 2022). Besides having economic value, fish is also susceptible to water pollution, potentially becoming a bio-indicator (Chovanec et al. 2003; Darwall & Vie 2005; Laffaille et al. 2005; Sarkar et al. 2008). Recently, the excessive level of anthropogenic activities, such as water pollution, habitat fragmentation, and the existence of invasive species, can reduce and threaten ichthyofauna biodiversity, especially endemic and native fish (Latuconsina 2020).

Temporarily, ichthyofauna studies in LEA were investigated by Kreemer (1922), followed by Wirjoatmodjo (1987), Hadiaty and Mun’im (1998), Defira and Muchlisin (2004), Hadiaty (2005), Haryono (2006), Muchlisin et al. (2015), Mardianti et al. (2018), and Maghfiriadi et al. (2019). The covering areas were the Alas River, Lembang River, Bahorok River, Tripa Peat Swamp, and Kluet River (Wirjoatmodjo 1987; Defira & Muchlisin 2004; Hadiaty 2005; Haryono 2006; Muchlisin et al. 2015; Mardianti et al. 2018; Maghfiriadi et al. 2019). Based on the previous studies, the Lembang River was reported to have the highest composition of fish species, followed by Alas River, Bahorok River, and Kluet River, which were 53, 52, 32, and 23 species, respectively. A previous study by Hadiaty (2005) reported several new species, including Osteochilus jeruk, Osteochilus serokan, Nemacheilus tuberigum, Mystus punctifer, Hemibagrus caveatus, and Kryptopterus piperatus. In contrast, Maghfiriadi et al. (2019) reported two introduced and invasive fish in the Alas River at LEA, namely Oreochromis niloticus (native from the northern of Africa and the Levante area) and Pterygoplichthys pardalis (native from the Amazon River basin).

The Merbau River is one of the rivers in the LEA that has not been studied for ichthyofauna. In contrast to the previous studies, which were dominant in the southwest region of the KEL, this river is located in the northern part of the LEA. Its upstream was administratively located in Tenggulun Subdistrict, while the estuary was in the Simpang Kiri Subdistrict, Aceh Tamiang Regency. Even though it is protected, illegal land conversion into palm plantations around the Merbau watershed has been massively occurring since 2000. Several adverse effects of this activity, mainly for the aquatic environment, were reported, including water pollution, erosion, and sedimentation.

Since 2014, the vegetation restoration program has been conducted around the Merbau River watershed. Around 230 hectares of palm plantation area were successfully restored until 2017 (Mongabay 2017). Referring to a similar program, Maghfiriadi et al. (2019) reported a positive effect between the vegetation restoration and rehabilitation program as well as increased fish composition (from 9 to 20 species) in the Alas River. Therefore, this study aims to describe the composition, diversity, biometric condition, potency, and conservation status of freshwater fish in Merbau River, LEA. The results might provide further reference and scientific information to prevent biodiversity loss.

2. Material and methods

Fish collection and identification

Fish sampling was carried out at six locations along the Merbau River with different habitat typologies. The location and characteristics of each station are presented in Table I and Figures 1 and 2. Fish were collected using gears, including throwing nets, gill nets, rods, and scoops. As many as three gill nets (50 × 1 m) with different mesh size were set at 09.00–15.00 Indonesian Western Time (WIB) and lifted every two hours. The mesh sizes used were 0.5, 1 and 2 inch, and the set distance between the nets was 50 m. Meanwhile, the throwing nets were spread 15 times at each station. Fish sampling was conducted for three days in each location. Furthermore, the collected fish were counted and sorted by species. The morphometric data, including total weight, total length (TL), standard length (SL), and fork length (FL), were measured with a digital scale and caliper at an accuracy of 0.01 g and 0.01 mm. For further identification, each fish species was preserved using 4% formalin and transferred into a labeled bottle. Identification of taxonomic groups was conducted using standard fish keys provided by Allen et al. (1990), Kottelat and Whitten (1996), Rachmatika (2004), Tan and Kottelat (2009), Official Fishbase website https://www.fishbase.se/, as well as Eschmeyer’s Catalog of Fishes (www.calacademy.org). Information related to local fish names was obtained from community interviews. Voucher specimens were transferred to 70% ethanol and deposited at the Laboratory of Ecology, Department of Biology, Faculty of Science and Technology, Universitas Islam Negeri Ar-Raniry (Lots ARY16102 to ARY16122, Table II).

Figure 1. Location of the study sites (sampling locations with green dot, Merbau River indicated with red line).

Figure 2. Sampled localities in the Merbau River, LEA. (A) Lubuk Ombo, (B) Kampung Selamat, (C) Kampung Tenggulun, (D) Alur Bujok, (E) Tenda Biru, (F) Tualang Tukul. Photographs by Siti Maulizar.

Table I. Description of research stations.

Station	Location	Coordinate	Description
1	Lubuk Ombo	N 04°02'03,22'' E 97°95'23,21''	The width of the river reaches ten meters with a depth of around four meters, the current was relatively fast. The substrate consists of small and sandy rocks. The brightness was high with greenish watercolor, the pH ranges from 8.2 to 8.8, and the DO ranges from 6.9 to 7.4 Mg/L, water temperature ranges from 24°C–26°C. The vegetation cover around the site was dominated by Meranti (Shorea sp.) and Teak (Tectona grandis) species.
2	Kampung Selamat	N 04°01'36,948'' E 97°57'17,22''	The river’s width reaches five meters with a depth of around five meters. The current was relatively fast. The substrate consists of small and sandy rocks. Low turbidity with turquoise watercolor. pH ranges from 8.5 to 8.1, and DO ranges from 6.5 to 7.2 Mg/L. Vegetation cover around the watershed includes meranti (Shorea sp.) and palm (Elaeis guineensis). Water temperature ranged from 25°C–27°C.
3	Kampung Tenggulun	N 04°02'05,36'' E 097°57'34,86''	The river’s width reaches eight meters with a depth of more than five meters. The current was relatively slow. The substrate consisted of gravel sand. Low brightness with brownish-green watercolor. pH ranged from 6.1 to 6.6, and DO ranged from 6.2 to 7.6 Mg/L. Water temperature ranged from 24–26°C. Vegetation around the river was ferns (Nephrolepis cordifolia) and palm (Elaeis guineensis)
4	Alur Bujuk	N 04°01'22,77'' E 097°58'14,86''	The river’s width reaches two meters with a depth of one point five meters. The current was relatively slow. The substrate was dominated by mud. The brightness was low with brownish-yellow watercolor. pH ranged from 5.8 to 6.4, and the DO ranged from 5.2 to 6.2 Mg/L. Water temperature ranged from 24–28°C. Vegetation around the river was dominated by grass (Cyperus rotundus) and shrubs (Cenchrus purpureus).
5	Tenda Biru	N 04°02'05,70'' E 097°57'54.92''	The river’s width reaches six meters with a depth of more than five meters. The current was relatively slow. The substrate was dominated by mud and sand. Watercolor was greenish. pH ranged from 8.4 to 9.1, and the DO ranged from 5.7 to 6.7 Mg/L. The temperature of the water ranged from 26°C–28°C. Vegetation around the river was dominated by shrubs (Cenchrus purpureus and Tridax procumbens), and palms (Elaeis guineensis).
6	Tualang Tukul	N 04°06'26,93'' E 97°98'73,68''	The river’s width reached eight meters with a depth of one point five meters. The current was relatively slow. The substrate was dominated by mud. The watercolor was brownish-yellow. pH ranged from 5.5 to 6.2, and the DO ranged from 5.4 to 6.1 Mg/L. The temperature of the water ranged from 26°C–28°C. Vegetation around the river was grass (Cyperus rotundus), shrubs (Cenchrus purpureus), and palms (Elaeis guineensis).

Table II. Taxonomic classification, local name, distribution pattern, conservation status and potency of fishes in Merbau River, LEA, Indonesia.

ORDER Family Species	Local Name	LO	KS	KT	AB	TB	TT	Total	IUCN	Potency	Voucher
CYPRINIFORMES
Cyprinidae
Crossocheilus cobitis (Bleeker, 1854)	Lemungkus	18	9	0	0	0	0	27	LC	C	ARY16110
Cyclocheilichthys apogon (Valenciennes, 1842)	Mata merah	3	0	0	20	2	5	30	LC	C	ARY16104
Hampala macrolepidota (Kuhl & van Hasselt, 1823)	Sebarau	0	4	0	2	3	4	13	LC	C	ARY16108
Labiobarbus leptocheilus (Valenciennes, 1842)	Sepui	0	0	5	9	3	0	17	LC	C	ARY16102
Mystacoleucus obtusirostris (Valenciennes, 1842)	Kempras	0	4	3	11	3	0	21	LC	C	ARY16106
Osteochilus vittatus (Valenciennes, 1842)	Paitan	0	4	15	32	10	9	70	LC	C	ARY16103
Oxygaster anomalura (van Hasselt, 1823)	Awur-awur	0	0	0	17	4	0	21	LC	C	ARY16109
Rasbora sumatrana (Bleeker, 1952)	Seluang	4	5	7	14	6	0	36	DD	C&O	ARY16105
Striuntius lateristriga (Valenciennes, 1842)	Gempual	0	2	8	11	8	0	29	LC	C&O	ARY16107
ANABANTIFORMES
Channidae
Channa lucius (Cuvier, 1831)	Gabus bujok	0	0	0	7	1	1	9	LC	C	ARY16112
Channa striata (Bloch, 1793)	Gabus sawah	0	0	0	6	2	2	10	LC	C	ARY16111
Pristolepididae
Pristolepis fasciata (Bleeker, 1851)	Keper	0	0	0	13	5	4	22	LC	C&O	ARY16113
SILURIFORMES
Clariidae
Clarias batrachus (Linnaeus, 1758)	Lele	0	0	0	10	0	2	12	LC	C	ARY16114
Clarias meladerma (Bleeker, 1846)	Lele batu	0	0	0	6	2	2	10	LC	C	ARY16115
Siluridae
Silurichthys phaiosoma (Bleeker, 1851)	Lempok	0	0	0	11	2	2	15	NT	C	ARY16116
Bagridae
Hemibagrus sabanus (Inger & Chin, 1959)	Keting	0	0	0	27	10	9	46	DD	C	ARY16117
Mystus nigriceps (Valenciennes, 1840)	Lambenatap	0	0	0	7	3	1	11	LC	C	ARY16118
SYNBRANCHIFORMES
Mastacembelidae
Macrognathus aculeatus (Bloch, 1786)	Sili	0	0	0	10	0	3	13	LC	C&O	ARY16119
Macrognathus maculatus (Cuvier, 1832)	Sili	0	0	0	8	0	2	10	LC	C&O	ARY16120
ANABANTIFORMES
Osphronemidae
Trichopodus trichopterus (Pallas, 1770)	Sepat	0	0	0	8	0	3	11	LC	O	ARY16121
BELONIFORMES
Zenarchopteridae
Zenarchopterus dispar (Valenciennes, 1847)	Cucut	0	1	0	0	0	0	1	LC	O	ARY16122
Total		25	29	38	229	64	49	434

Note: LO: Lubuk Ombo, KS: Kampung Selamat, Kampung Tenggulun, AB: Alur Bujok, TB: Tenda Biru, TT: Tualang Tukul. Global conservation status according to IUCN. LC: least concern, NT: near threatened, and DD: data deficient. Potency: C: Consumption, O: Ornamental.

Diversity indices

Diversity indices, including the Shannon-Wiener diversity index (H’), the Simpson evenness index (E), the Simpson dominance index (C), and the Sorensen similarity index (SI) between sampling areas, were measured. The measurement of the Shannon-Wiener diversity index (H’) was calculated as follows Shannon and Wiener (1963):

$H{ }^{\text{rsquo}}=-\mathrm{\Sigma }pilnpi$

where H′ = Shannon – Weiner index, pi = the proportion of density of i^th species (pi = ni/N), “ni” is the density of each species in the sample, and “N” is the density of individuals of all species. The Simpson evenness index (E) was calculated as follows:

$E=H{ }^{\text{rsquo}}/Hmaks$

where, E = Evenness index, H = Diversity index, Hmax = ln S, S = Number of species found. The Simpson dominance index (C) was calculated as follows:

$C=\hspace{0.17em}\mathrm{\Sigma }\hspace{0.17em}{\left(pi\right)}^2$

where C = The Simpson dominance index, pi = the proportion of density of i^th species (pi = ni/N), “ni” is the density of individuals of each species in the samples, and “N” is the density of individuals of all species. The Sorensen similarity index (SI) was calculated as follows:

$\mathrm{S}\mathrm{I}=2\mathrm{C}/\left(\mathrm{A}+\mathrm{B}\right)$

Where A = the number of all fish species in location A, B = the number of all fish species in location B, and C = the number of common species (present in both locations A and B).

Length-weight relationship, length-length relationship, and condition factor

Length-weight relationship of fish was calculated using the following equation: W = aL^b. Where W = fish total weight (g), L = fish total length (mm), a = intercept, and b = fish growth coefficient. The relationship between total (TL), standard (SL), and fork length (FL) was measured using a simple linear regression equation, namely TL = a + b*SL and TL = a+ b*FL (Rosli & Isa 2012). The condition factor (K) was calculated using the formula: K = W × 100/L³ (Ricker 1973). Only fish species with at least three individuals were counted and examined.

Potency and conservation status

The potency of fish was divided into consumption and ornamental categories. Fish consumption was identified based on interviews with local communities regarding its taste, availability, and price. Meanwhile, ornamental fish was determined by referring to the color of the scales, fins, morphology, body color patterns, and behavior (Muchlisin 2013; Maghfiriadi et al. 2019). The conservation status was evaluated based on the IUCN (International Union for Conservation of Nature) website https://www.iucnredlist.org/.

3. Results

Species composition

This study reported 21 species (434 individuals) of fish belonging to six orders and nine families spatially distributed randomly among six stations (Table II, Figures 3 and 4). Osteochilus vittatus was the predominant species collected (70 individuals), followed by Hemibagrus sabanus (46 individuals), Rasbora sumatrana (36 individuals), and Cyclocheilichthys apogon (30 individuals). In contrast, Zenarchopterus dispar was the least species collected, with only one individual. The families of Cyprinidae was the most represented family (nine species; 42.9%). Each of Clariidae, Channidae, Bagridae, and Mastacembelidae family has two species (9.5%) representation; likewise, each of Osphronemidae, Siluridae, Zenarchopteridae, and Prestolepidae has one species (4.8%) representation in the fish composition (Figure 5). Based on the sampling stations, Alur Bujok has the highest family, species, and specimens contribution, with eight families, 19 species, and 229 specimens. Meanwhile, Lubuk Ombo has the lowest values, with a single family, three species, and 25 specimens (Figure 6).

Figure 3. Fish species from Cyprinidae. (1) Crossocheilus cobitis; (2) Cyclocheilichthys apogon; (3) Hampala macrolepidota; (4) Labiobarbus leptocheilus; (5) Mystacoleucus obtusirostris; (6) Osteochilus vittatus; (7) Oxygaster anomalura; (8) Rasbora sumatrana; (9) Striuntius lateristriga. Scale bar = 50 mm.

Figure 4. Fish species from Channidae, Prestolepididae, Clariidae, Siluridae, Bagridae, Mastacembelidae, Osphronemidae, Zenarchopteridae. (10) Channa lucius; (11) Channa striata; (12) Prestolepis fasciata; (13) Clarias batrachus; (14) Clarias meladerma; (15) Silurichthys phaiosoma; (16) Hemibagrus sabanus; (17) Mystus nigriceps; (18) Macrognathus maculatus; (19) Macrognathus aculeatus; (20) Trichopodus trichopterus; (21) Zenarchopterus dispar. Scale bar = 50 mm.

Figure 5. Percentages of the different families of fishes in Merbau River.

Figure 6. Distribution of families, species and specimens according to sampling stations.

Species diversity

The diversity and evenness indexes of fish species in the Merbau River at LEA were categorized as medium (H’ = 2.52) and stable (E = 0.85). The Alur Bujok has the highest diversity (H’ = 2.55; medium), while Tenda Biru has the highest evenness index values (E = 0.92; stable community). In contrast, Lubuk Ombo has the lowest diversity (H’ = 0.78; low category) and evenness index value (E = 0.71; unstable community) (Table III). The dominance index of fish was categorized as low (C = 0.07). The highest and lowest values were detected in Kampung Tenggulun (C = 0.74; medium category) and the Alur Bujok (C = 0.07; low category) (Table III). Furthermore, the composition of fish in the Alur Bujok tended to be similar to Tenda Biru and Tualang Tukul, with the similarity index values ranging from 75.86–84.85%. The lowest was observed between Kampung Tenggulun and Tualang Tukul, with a value of 10.52% (Table IV).

Table III. Diversity indices of fishes according to sampling stations in Merbau River.

Diversity variables	Lubuk Ombo	Kampung Selamat	Kampung Tenggulun	Alur Bujok	Tenda Biru	Tualang Tukul	Overall
Shannon-Wiener (H')	0.78	1.78	1.47	2.55	2.50	2.41	2.52
Evenness (E)	0.71	.91	.91	0.87	0.92	0.85	0.85
Dominance (C)	0.55	.18	.74	0.07	0.09	0.10	0.07

Table IV. Similarity index (%) of fishes in Merbau River.

Research stations	Lubuk Ombo	Kampung Selamat	Kampung Tenggulun	Alur Bujok	Tenda Biru	Tualang Tukul
Lubuk Ombo		4.00	25.00	18.18	22.22	11.76
Kampung Selamat			66.67	38.46	45.45	19.05
Kampung Tenggulun				50.00	50.00	10.52
Alur Bujok					82.35	84.85
Tenda biru						75.86
Tualang Tukul

Length-weight relationship, length-length relationship, and condition factor

All fish collected had negative allometric patterns with b coefficient values ranging from 1.17–2.51 (Table V). The highest and lowest value of b was observed in Osteochilus vittatus and Trichopodus trichopterus. Based on the total length-standard relationship, the highest and lowest coefficient a (slope) value was recorded in Crossocheilus cobitis (TL = 38.72 + 0.84 SL) and Macrognathus maculatus (TL = 3.24 + 1.03 SL). However, Macrognathus maculatus and has the highest value of the coefficient of b (TL = 3.24 + 1.03 SL), while Hampala macrolepidota and Striuntius lateristriga have the lowest value (TL = 37.06 + 0.68 SL) (Table VI). Based on the total length-fork relationship, the highest and lowest coefficient a (slope) value was recorded in Hemibagrus sabanus (TL = 24.84 + 0.87 FL) and Oxygaster anomalura (TL = 0.61 + 1.02 FL). Silurichthys phaiosoma has the highest value of the coefficient of b (TL = 10.49 + 1.11 FL), while Hampala macrolepidota (TL = 20.14 + 0.82 FL) and Striuntius lateristriga (TL = 20.13 + 0.82 FL) have the lowest value (Table VI). The highest and lowest condition factor was recorded in Osteochilus vittatus (K = 1.47) and Hemibagrus sabanus (K = 0.78) (Table V).

Table V. Estimated parameters from length–weight relationship of fishes in Merbau River. a: intercept; b: slope of the linear regression; Cl: confidence limits; R²: coefficient of determination; K: condition factor.

Spesies	Total Length (mm)		Total Weight (g)		a	b	CI b of 95%	R^2	K	Growth pattern
	Min	Max	Min	Max
Channa lucius	146.47	448.48	76.25	497.68	0.0076	1.81	1.70–1.90	0.95	1.01	negative allometric
Channa striata	120.23	381.46	57.45	622.26	0.0037	2.01	1.60–2.43	0.97	1.01	negative allometric
Clarias batrachus	153.05	251.23	73.45	180.54	0.0063	1.85	1.73–1.97	0.99	0.99	negative allometric
Clarias meladerma	156.2	244.32	62.81	164.32	0.0017	2.08	1.79–2.37	0.97	1.01	negative allometric
Crossocheilus cobitis	89.12	142.77	7.28	27.28	0.0002	2.27	1.54–3.01	0.61	1.24	negative allometric
Cyclocheilichthys apogon	75.75	147.54	29.04	95.18	0.0097	1.83	1.67–2.00	0.95	1.00	negative allometric
Hampala macrolepidota	115.81	186.49	27.02	66.34	0.0007	2.18	1.72–2.65	0.90	0.93	negative allometric
Hemibagrus sabanus	107.78	185.13	11.33	66.62	0.0001	2.50	2.13–2.86	0.80	1.40	negative allometric
Labiobarbus leptocheilus	103.59	145.43	50.98	91.88	0.0094	1.85	1.61–2.09	0.94	1.24	negative allometric
Macrognathus aculeatus	133.24	292.75	12.64	67.43	0.0020	1.83	1.42–2.24	0.92	1.12	negative allometric
Macrognathus maculatus	86.18	307.01	8.72	68.21	0.0007	2.03	1.61–2.45	0.91	1.10	negative allometric
Mystacoleucus obtusirostris	97.85	143.23	45.24	95.56	0.0095	1.85	1.74–1.97	0.98	1.00	negative allometric
Mystus nigriceps	88.36	153.32	12.18	48.23	0.0012	2.10	1.69–2.50	0.93	0.96	negative allometric
Osteochilus vittatus	49.89	217.33	5.43	65.82	0.0001	2.51	2.33–2.69	0.92	1.47	negative allometric
Oxygaster anomalura	40.02	62.32	3.02	7.54	0.0073	1.62	1.38–1.87	0.90	0.99	negative allometric
Pristolepis fasciata	83.55	128.81	24.21	75.72	0.0010	2.31	2.02–2.60	0.93	1.02	negative allometric
Rasbora sumatrana	62.90	115.80	4.07	18.68	0.0002	2.40	2.06–2.73	0.86	0.78	negative allometric
Silurichthys phaiosoma	112.02	183.48	17.61	65.49	0.0002	2.36	1.51–3.22	0.73	1.26	negative allometric
Striuntius lateristriga	64.49	100.56	13.23	40.29	0.0004	2.48	2.29–2.66	0.96	1.02	negative allometric
Trichopodus trichopterus	65.87	95.67	7.19	12.45	0.0519	1.17	0.63–1.72	0.72	1.00	negative allometric

Table VI. Estimated parameters from relationship between total length (TL), standard length (SL) and fork length (FL) of fishes in Merbau River.

Species	SL (min-max)	FL (min-max)	Equation (TL-SL)	R^2	Equation (TL-FL)	R^2
Channa lucius	123.77–425.78	132.87–434.88	TL = 20.95 + 0.98 SL	0.98	TL = 12.62 + 0.98 FL	0.97
Channa striata	100.76–373.66	111.46–378.16	TL = 25.01 + 0.96 SL	0.97	TL = 9.57 + 0.98 FL	0.98
Clarias batrachus	145.31–241.43	150.43–248.11	TL = 20.11 + 0.93 SL	0.98	TL = 15.60 + 0.93 FL	0.99
Clarias meladerma	145.70–237.82	150.88–240.02	TL = 14.84 + 0.97 SL	0.98	TL = 6.72 + 0.99 FL	0.99
Crossocheilus cobitis	65.67–120.21	80.67–139.44	TL = 38.72 + 0.84 SL	0.75	TL = 12.67 + 0.92 FL	0.94
Cyclocheilichthys apogon	55.94–130.69	64.73–134.16	TL = 24.24 + 0.92 SL	0.94	TL = 16.37 + 0.93 FL	0.96
Hampala macrolepidota	105.81–176.49	107.31–177.99	TL = 37.06 + 0.68 SL	0.69	TL = 20.14 + 0.82 FL	0.83
Hemibagrus sabanus	90.12–153.95	100.67–164.82	TL = 36.84 + 0.85 SL	0.89	TL = 24.84 + 0.87 FL	0.90
Labiobarbus leptocheilus	75.35–127.32	85.19–136.36	TL = 33.78 + 0.89 SL	0.85	TL = 20.51 + 0.91 FL	0.82
Macrognathus aculeatus	128.74–288.25	130.14–290.65	TL = 5.22 + 0.96 SL	0.92	TL = 2.47 + 0.99 FL	0.99
Macrognathus maculatus	70.89–290.81	74.08–239.91	TL = 3.24 + 1.03 SL	0.92	TL = 4.36 + 1.07 FL	0.95
Mystacoleucus obtusirostris	83.50–134.38	90.39–138.07	TL = 20.38 + 0.93 SL	0.91	TL = 11.31 + 0.98 FL	0.94
Mystus nigriceps	74.94–145.21	81.84–149.85	TL = 14.68 + 0.96 SL	0.98	TL = 6.29 + 0.99 FL	0.96
Osteochilus vittatus	42.94–205.55	39.04–196.43	TL = 27.44 + 0.95 SL	0.93	TL = 17.00 + 0.96 FL	0.89
Oxygaster anomalura	31.76–57.67	37.83–62.92	TL = 5.90 + 0.98 SL	0.81	TL = 0.61 + 1.02 FL	0.98
Pristolepis fasciata	71.35–122.61	81.65–128.43	TL = 23.98 + 0.84 SL	0.97	TL = 3.00 + 0.98 FL	0.98
Rasbora sumatrana	47.50–109.19	51.65–113.63	TL = 19.25 + 0.96 SL	0.86	TL = 19.25 + 0.96 FL	0.86
Silurichthys phaiosoma	95.69–168.62	103.38–165.67	TL = 27.44 + 0.95 SL	0.85	TL = 10.49 + 1.11 FL	0.92
Striuntius lateristriga	50.40–92.01	56.08–96.56	TL = 37.06 + 0.68 SL	0.69	TL = 20.13 + 0.82 FL	0.83
Trichopodus trichopterus	58.37–89.17	60.89–91.57	TL = 9.40 + 0.97 SL	0.91	TL = 3.17 + 0.99 FL	0.98

Potency and conservation status

A total of 24% of fish species collected have the potential to be utilized both as consumption fish and ornamental fish, 9% have the potential as ornamental fish, and 67% have the potential as consumption fish (Figure 7(b)). Some consumption fish with high economic value, including Hampala macrolepidota (4.60–6.57 USD/kg), Macrognathus aculeatus, and Macrognathus maculatus (5.52–7.88 USD/kg), and Osteochilus vittatus (2.63–3.94 USD/kg). Trichopodus trichopterus and Zenarchopterus dispar were potentially ornamental due to their color patterns, unique body shapes, and varied patterns (Figure 4 number 20–21). The conservation status of fish in the Merbau River was divided into three categories, namely Least concern (18 species), Data deficient (2 species), and Near Threatened (1 species) (Table II, Figure 7(a)).

Figure 7. Diagram of the IUCN red list status (A) and Venn diagram of potency (B) of 21 species of fish in Merbau River. LC: least concern, DD: data deficient, and NT: near threatened. Potency: C: Consumption, O: Ornamental.

4. Discussion

As many as 12 of 21 fish species in the Merbau River were also detected in the rivers located south-west of LEA (Alas River, Lembang River, Bahorok River, Kluet River, and rivers around Tripa Peat Swamp). These species include Osteochilus vittatus, Cyclochtheilichthys apogon, Rasbora sumatrana, Mystacoleucus marginatus, Hampala macrolepidota, Channa striata, Channa lucius, Silurichthys phaiosoma, Mystys nigriceps, Macronagthus maculatus, Macronagthus aculeatus, and Trichogaster trichopterus (Defira & Muchlisin 2004; Hadiaty 2005; Muchlisin et al. 2015; Mardianti et al. 2018; Maghfiriadi et al. 2019). Meanwhile, four fish species were recorded in the northern part of LEA (Bahorok River), including Mystacoleucus marginatus, Mystys nigriceps, Channa striata, and Trichogaster trichoperus (Haryono 2006). Interestingly, Striuntius lateristriga, Oxygaster anomalura, Crossocheilus cobitis, Pristolepis fasciata, Clarias meladerma, Silurichthys phaiosoma, and Zenarchopterus dispar were first reported in the river of LEA.

The number of fish orders found in the Merbau River (6) were still lower than other rivers in the LEA including Lembang River (13), Kluet River (12), Tripa Peat Swamp (10), Bahorok River (9), and Alas River (8) (Defira & Muchlisin 2004; Hadiaty 2005; Haryono 2006; Muchlisin et al. 2015; Mardianti et al. 2018; Maghfiriadi et al. 2019). Cypriniformes, Anabantiformes, Siluriformes, Synbranchiformes, and Beloniformes were also found in the rivers in the South West of LEA. Meanwhile, only Cypriniformes, Siluriformes, Anabantiformes, and Synbranchiformes were similar to river in northern of LEA (Haryono 2006).

The composition of fish species in aquatic ecosystems might be influenced by several factors, such as physicochemical water parameters and food availability (Gebrekiros 2016; Burgos-Aceves et al. 2019). Differences in habitat characteristics between the LEA’s west-south and northern rivers might be the main factors influencing the variation in fish composition. The south-west area was reported to consist of more rivers with more varied environmental conditions, including large rivers, tributaries, small channels, and estuaries (Defira & Muchlisin 2004; Hadiaty 2005; Muchlisin et al. 2015; Maghfiriadi et al. 2019). Additionally, the vegetation around the rivers in the south-west of the LEA was still relatively natural and well-maintained. In contrast, the environmental conditions of rivers in the northern part tend to be more homogeneous and accompanied by many land conversions around the river. Degradations in the forest cover areas in the Aceh Tamiang Regency watersheds that might be responsible for sedimentation and water quality changes. The shrinking of fish composition due to the high level of sedimentation has been reported in other rivers, including the Ganges, India (Vass et al. 2010), Sironko (Turyahabwe et al. 2022), and rivers in the Alpine (Scheurer et al. 2009).

Cyprinidae was the predominant family in the Merbau River, with 42.9% of the total fish found. This percentage was relatively high compared to other rivers of LEA, such as the Lembang and Ketambe River (14%) (Hadiaty 2005) and the Bahorok River (31%) (Haryono 2006). However, it was still lower compared to the Kluet River (57%) (Mardianti et al. 2018) and Alas River (50%) (Defira & Muchlisin 2004; Hadiaty 2005; Maghfiriadi et al. 2019). The dominance of the Cyprinidae family has also been reported in several other rivers in Indonesia, including the Enim River, South Sumatra (Hamidah 2004), rivers in the Tesso Nilo area, Riau (Rachmatika et al. 2006) and Kampar Kanan River, Riau (Aryani 2015)

Hubert et al. (2015) stated that Cyprinidae was the dominant fish family in the Indonesian freshwater ecosystem, especially in areas on the Sunda shelf. However, the Cyprinidae family tends to be sensitive to the alteration of the aquatic environment. Previous research revealed a decrease in Cyprinidae family composition due to water pollution in rivers, for instance, the Karnataka River, India, and Pahang River, Malaysia (Shetty et al. 2015; Rashid et al. 2018).

Osteochilus vittatus was the predominant fish caught, which was 70 individuals. This species was also reported recorded in other LEA rivers, such as Alas River (Maghfiriadi et al. 2019), Kluet River (Mardianti et al. 2018), and rivers around Tripa Peat Swamp (Muchlisin et al. 2015). The high population has also been reported in other waters in Indonesia, such as the Kepari and Emperas River, West Kalimantan (Siska et al. 2020), Benanga reservoir, East Kalimantan (Jusmaldi et al. 2020), and Lake Talaga, Central Sulawesi (Muryanto & Sumarno 2016). The abundance of Osteochilus vittatus might be influenced by its ability to spawn throughout the year and its adaptability toward the fluctuations of water conditions (Putri et al. 2015; Madihah et al. 2021). Zenarchopterus dispar appears to be the most diminutive species which only has one individual. The presence was first reported in LEA and only detected at Kampung Selamat Station, Merbau River. The river around this station had specific characteristics, such as the relatively high torrent, river basins/bottoms, substrate dominated by gravel and sand, and fern vegetation around the river. The characteristics of this habitat and the minor abundance of Zenarchopterus dispar were almost similar to other river locations where this type of fish was discovered.

Based on locations, the highest composition of fish species was found in Alur Bujok (19 species), followed by Tenda Biru (15 species) and Tualang Tukul (14 species). The similarity index (IS) analysis showed that the composition of fish in these stations was similar (IS value = 75.86–84.85%). Alur Bujok was also the location with the highest diversity index. High species composition and similarity were closely related to the characteristics of the habitat and its location, which was included in the downstream area of the river. Power et al. (2013) and Humphries et al. (2020) stated that the downstream area of the river was broader and accompanied by highly abundant feed availability, resulting in increasing fish species and populations. A high composition of fish species in the downstream area was also reported in the Alas River (Maghfiriadi et al. 2019).

Analysis of the diversity index showed that the Merbau River was categorized as moderate (2.52). Fish diversity index in the moderate category was also reported in Kluet River (H’ = 1.52–2.30) (Mardianti et al. 2018) and the Alas River (H’ = 1.43–2.03) (Defira & Muchlisin 2004). Based on the evenness index, the Merbau River ecosystems are included in the stable category (E = 0.91). The stable community category was also reported in Alas River (E = 0.93) (Defira & Muchlisin 2004) and Tripa Peat Swamp (E = 0.81) (Muchlisin et al. 2015).

Information regarding the conservation status of fish in the LEA has not been widely reported. The availability of data related to the conservation status in LEA waters was only reported in the Alas River (Maghfiriadi et al. 2019). Based on the IUCN conservation status category, most Merbau River fish were considered the least concerned at 85.7%. These results are similar to the Alas River (LEA) and several others in Indonesia, such as Unda River (Indrawan et al. 2021), Way Sindalapai River (Juriani et al. 2020), and Cimanuk River (Herawati et al. 2020). The lack of information related to the conservation status of fish is inseparable from reduced attention to ichthyological studies. Hadiaty et al. (2019) reported that limited funds, research support facilities, and the difficulty of adapting to various ethnic groups and cultures are the major obstacle that hinders the diversity assessment of ichthyofauna. Therefore, further studies are needed to keep the information updated regarding the potential of fish switching/changing status, e.g., Zenarchopterus dispar (the least abundance fish).

As many as 14 species of fish collected have the potential to be used as consumption fish, five species of fish are bi-potential as both consumption and ornamental fish, and two other species have potential only as ornamental fish. Compared to other rivers in LEA, the number of fish that have the potential to be consumed from the Merbau River was higher than the Alas River (16 species) but similar to the rivers around Tripa Peat Swamp (18 species) (Muchlisin et al. 2015), and the Bahorok River (20 species). Ornamental fish from the Merbau River was still lower than those in Bahorok River, Alas River, and Rawa Tripa Peat Swamp consisting of 20, 12, and 20 species, respectively (Haryono 2006; Muchlisin et al. 2015; Maghfiriadi et al. 2019). Studies related to the potential of each type of fish are essential for the optimal utilization of fishery resources while paying attention to aspects of sustainability (Rochette et al. 2014; Su et al. 2020).

Information regarding biometric conditions (length to weight, length to length, and conditional factors) is needed in order to examine the general health of fish populations and assist in estimating the recruitment potential in population dynamics studies (Hossain et al. 2012; Kumar et al. 2013; Lim et al. 2013). The results showed that the growth patterns of all fish collected are in the negative allometric category. The dominance of fish with these patterns is also found in several other rivers, including the Torsa River, India (Koushlesh et al. 2017) and the Basistha River, India (Borah et al. 2017). Osteochilus vittatus is one type of fish that tends to have a fluctuating growth pattern. In this study, Osteochilus vittatus has a negative allometric growth pattern which is similar to Lake Telaga (Putri et al. 2015) and the waters of Rawa Pening (Rochmatin et al. 2014). In contrast, Osteochilus vittatus collected from the Benanga Reservoir, East Kalimantan showed allometric positive growth pattern (Jusmaldi et al. 2020). Differences in fish growth patterns between habitats can be influenced by several factors, such as the availability of fish feed, competition between populations, and the level of gonad maturity (Muchlisin et al. 2010; Batubara et al. 2019).

5. Conclusions

The study of ichthyofauna in the Merbau River recorded 21 species of fish belonging to six orders and nine families, where Cyprinidae was the most dominant family at 42.9%. Analysis of the diversity index shows that the river belongs to the moderate diversity index (H’ = 2.52) and stable condition (E = 0.85). From the classifications, five species have potential both as consumption and ornamental fish, 14 species as consumption fish, and two species was included in the ornamental category. The conservation status of fish in the Merbau River was categorized into three categories: Least concern (85.7%), Data deficient (9.5%), and Near Threatened (4.8%). The further study related to fisheries biology and population dynamics in the LEA is necessary to support sustainable management program.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was funded by a research grant from the Center of Research and Community Service, Universitas Islam Negeri Ar-Raniry under the ‘‘Penelitian Pengembangan Perguruan Tinggi 2021” Scheme [Reg No. 211040000045511].