Diversity and distribution of fish in the Lokop river, Leuser Ecosystem Area, Indonesia

ABSTRACT


Introduction
Lokop River is located in Leuser Ecosystem Area, Serbajadi District, East Aceh Regency, Aceh Province.This river flows from the upper reaches of Central Aceh Regency to East Aceh Regency.Information on the existence of fish species and fish distribution in the Lokop River has not been widely published (Mawardi and Yusrizal, 2017).Meanwhile, the existence of these fish is now threatened by various factors, including destructive fishing (toxin and electric shocks), global climate change and environmental pollution resulting in a decline in fish populations (Defira and Muchlisin, 2004;Maghfiriadi et al., 2019).
Fish plays an important role in river ecosystems because it can be used as a food source and bioindicator of water quality (Nurudin et al., 2013).The distribution of fish is also determined by biotic, abiotic and human activity factors.The existence of ecological changes to river waters can affect the diversity of fish in the river.The diversity of fish species is also determined also by habitat characteristics that affect the presence of fish in the aquatic environment (Syafei, 2017).Previous fish diversity studies have been conducted in several areas such as the Kluet River in South Aceh (Mardianti et al., 2017), Alas River in Subulussalam (Maghfiriadi et al., 2019).The results of the study revealed that the level of fish diversity in Aceh waters were in the moderate categorized.
Information about the diversity and distribution of fish in the Lokop River is rare, from previous studies, only one species of fish was studied and generally the type studied was a native species in the river.The study included the meristic and morphometric diversity of Keureuling fish (Tor spp.) (Thaib, 2012) and the food habiets of Jurung fish (Tor soro) (Mawardi and Yusrizal, 2017).Hence, this study aims to analyze the level of diversity and distribution patterns of fish in the Lokop River in the Leuser  Maghfiriadi et al. (2023) Ecosystem Area.
Information about the diversity and distribution of fish in the Lokop River is rare, from previous studies, only one type of fish was studied and generally the type studied was a native species in the river.The study included the meristic and morphometric diversity of Keureuling fish (Tor spp.) (Thaib, 2012) and the food habiets of Jurung fish (Tor soro) (Mawardi and Yusrizal, 2017).Hence, this study aims to analyze the level of diversity and distribution patterns of fish in the Lokop River in the Leuser Ecosystem Area.

Location and time of research
This research was carried out from June to August 2022.Data collection was carried out using purposive sampling methods, at five stations along the river flow divided according to different habitat typologies.The research locations and descriptions of each research station are presented in Figure 1 and Table 1.The identification of fish samples was carried out at the Biosystematics Laboratory of the Faculty of Mathematics and Natural Sciences, Syiah Kuala University, Banda Aceh.
The method of physical-chemical analysis of water used in the Lokop River uses the in situ method.The physical parameters analyzed are temperature, brightness and current velocity, while the chemical parameters are pH and dissolved oxygen (DO).Water quality parameters such as temperature (°C) were measured using a digital thermometer ( MTA-37163967, Made in China), pH and Dissolved Oxygen (mg L -1 ) were calculated using a digital water quality checker (Lutron WA-2017SD, Made in Taiwan), current water were measured using current meter (FLOWATCH FL-03, Made in Swiss), water brightness is measured using a secchi disk and GPS (Global Position System) which functions to mark the coordinates of observation stations (Garmin 64s, Made in Indonesian).The location of the river ranges from 10 meters with a river depth range of more than 3 meters, relatively fast currents, high brightness with greenish water conditions, pH ranging from 7-7.5 and dissolved oxygen ranging from 6.5-7.9 mg/L, water temperature 25 °C, vegetation around the river in the form of trees and shrubs.

Sample collection and identification
The study site was divided into 5 observation stations based on the typology of river habitat, each observation station was divided into three substations representing parts of the basin, river bank and river basin approximately 50 m apart.Sampling was carried out at each observation station using a plot of 10 x 10 m 2 .The number of plots at each station is 9 plots with a total of 45 plots in total (Sukmono et al., 2013).
The fish samples caught grouped based on the same morphological characteristics to calculate the amount of each species.Before preserving, each large fish species placed on a tray equipped with a contrasting background and a ruler placed at the bottom of the fish as a scale for comparison (Zulfahmi et al., 2022), then photographed using a Canon EOS 1500D camera in a fresh state with the head facing left (Sukmono et al., 2013), while taking pictures for small fish was done after the fish were put in the aquarium and then photographed alive so that the colors captured were clearer (Maghfiriadi et al., 2019).For further identification, each species was taken three individual as an spesimen, then put into a collection bottle containing 4% formalin and labeled (Saanin, 1984).Identification of fish samples based on morphological and morphometric features refers to the identification book belonging to Rachmatika et al. (2002), Kottelat and Whitten (2009), Rainboth et al. (2012) and fishbase official website https:www.fishbase.se/(Froese and Pauly, 2019).

Research Parameters
The parameters observed in this study are the level of diversity and distribution patterns (Fachrul, 2007).Shannon-Wiener species diversity index calculated by formula as follow:

Diversity index
The diversity index is divided into three categories, namely low (H'<1), moderate (H'=1-3) dan high (H'>3).Based on the results of the diversity index analysis obtained during the research in Lokop River, overall it is included in the category of moderate diversity index.The diversity index Morisita index formula as follow Table 2.

Distribution pattern
The results of the distribution pattern analysis are known that the distribution pattern of fish in the Lokop River has a uniform pattern and clusters.Of the total 17 species obtained, as many as 8 (47%) were uniformly distributed, 8 species (47%) were scattered in clusters and 1 species (6%) could not be analyzed because only one individual was found.The pattern of distribution of fish species in the Lokop River was presented in Table 3.

Discussion
The fish diversity index in the Lokop River is catagorized as moderate category (H'=2.39).The value of the diversity index is influenced by the number of individuals of each species of fish and the total number of individuals of all fish species.The diversity index value is high if the population of each species is almost the same and the diversity index is low if there are certain species that dominate, so that the population of each species is uneven (Arhas et al., 2015).Species diversity is also influenced by environmental factors such as pH, dissolved oxygen, current velocity and brightness.This is in accordance with the opinion of Ulfah et al. (2019) which states that the high and low value of diversity in a body of water indicates an influence on environmental factors (temperature, pH, dissolved oxygen, current velocity, brightness) and the availability of fish feed in the waters.In addition, the carrying capacity of environmental factors is also very influential for the growth and development of fish, because each  Maghfiriadi et al. (2023) species of fish has certain environmental limiting factors.
Fish are organisms that have an ecological function in rivers whose existence is influenced by aquatic environmental factors.Table 4 shows that the water temperature of the Lokop River ranges from 24-28 0 C. Variations are due to differences in the influence of plant vegetation cover levels around river waters.These temperature conditions are still at an ideal level for fish growth.According to Kenconojati et al. (2016) the optimum temperature for fish growth ranges from 20-30 0 C, and the day and night temperature difference in the tropics tends to be smaller by < 5 0 C.
The highest brightness was obtained at station 4 at 61 cm and the lowest at station 5 at 32 cm.The difference in brightness is influenced by the bottom substrate and material suspended in river water, the brigthness of the river water is getting lower downstream of the river width tends to be wider and the current is relatively slow, so that a lot of material dissolved in the water has the potential to reduce the brigthness of the waters.This is in line with the opinion of Sinambela and Sipayung (2015) that stated the low brigthness is influenced by particels and sediments washed away by river flows from land erosion.According to Fauziah ( 2022), the brightness level is affected by the turbidity of the water, the low brightness is caused by high turbidity meanwhile low turbidity causes high brightness.Brightness has an important role in the photosynthesis process of phytoplankton organisms, good brightness helps light penetrate more waters and can make it easier for phytoplankton to carry out photosynthesis.According to Suin (2002) light penetration is influenced by the amount of dissolved solids that are in the waters of rivers or water bodies with high dissolved solids causing the water to become cloudy so that the penetration of light into the water is reduced and will decrease the feeding efficiency of aquatic organisms.
The Lokop River has a current velocity ranging from 0.16 -0.48 m/s.Based on this category, the Lokop River is included in the category of mediumwinded.The velocity of currents in a body of water greatly affects the value of diversity, distribution patterns, composition and behavior of fish, where the velocity of currents also has an impact on other abiotic factors.According to Sriwidodo et al. (2013) water currents are the movement of a water mass that is very important for aquatic life, because currents have a role in providing transportation of nutrients, plankton and fish larvae and other biota to move from one place to another.This is in accordance with the results of the study Erika et al. (2018) expresses the velocity of medium current which is in the range of (0.25 -0.5 m/s).Current velocity can be influenced by many things including the presence of wind, the slope of the water topography, the type of water bottom substrate, water discharge and rainfall (Kinanti et al., 2014).
The degree of acidity (pH) is a value to determine the acidity level of a water.The pH value in the Lokop River ranges from 7.8 -8.Human activities along river flows and the amount of organic or inorganic waste that enters the waters can affect the pH conditions in these waters.Acidic or alkaline water conditions can endanger the survival of organisms, because they will interfere with metabolism and respiration.The level of tolerance of aquatic organisms to pH varies greatly, but in general most aquatic organisms are very sensitive to changes in pH (Mainassy, 2017).The influence of pH on the diversity and distribution of fish in waters greatly affects the adaptability of fish to the conditions of the waters they occupy, if there is an increase or decrease in the degree of acidity in the waters will also have an impact on the immune system of fish which can affect fish health so that it will decrease the abundance of fish.
Dissolved oxygen (DO) is a compound that is very important for the life of aquatic organisms, especially for the respiratory process.Dissolved oxygen in the Lokop River in the Leuser Ecosystem Area ranges from 6.4 -7.7 mg/L.Dissolved oxygen is highest at station 4 and lowest at station 5. Based on the quality standards of the Government Regulation of the Republic of Indonesia.No. 22 of 2021 (Class II), the range of dissolved oxygen for fish farming activities is > 4 mg / L. The presence of dissolved oxygen in the waters is an important factor for the survival of all aquatic organisms.Kenconojati et al. (2016) states that good dissolved oxygen levels for fish growth are above 5 mg/L.Low concentrations of dissolved oxygen can result in fish and dead water biota.
The results of distribution pattern analysis generally show clustered distribution patterns.The distribution of fish in a region depends on habitat type, vegetation and environmental factors (current velocity, pH, dissolved oxygen and brightness).The uniform distribution pattern is very common in aquatic environments in fish habitats compared to clustered patterns.The uniform distribution pattern is caused by relatively homogeneous aquatic environmental factors can be detected from temperature, pH and dissolved oxygen conditions and competition between individuals in fighting for Depik Jurnal Ilmu-Ilmu Perairan, Pesisir dan Perikanan Volume 12, Number 1, Page 12-18 Maghfiriadi et al. (2023) food so that there is an even division of space.According to Odum (1996), organisms with a uniform distribution pattern are thought to be able to utilize all environmental factors so that they are found in all gradients in the habitat.Grouping distribution patterns occur due to the absence of competition between species in meeting the needs of food resources.According to Wahyuni et al. (2022), clustering distribution can occur due to the gathering of individuals in a habitat as a strategy to respond to changes in weather and seasons, as well as changes in habitat and reproductive processes.This makes it easier for fish to adapt to changing environmental conditions when in clustered distribution.

Conclusion
Fish diversity in the Lokop River is in the moderate category (H' = 2.39).The distribution pattern of fish in the Lokop River is classified as clusters and uniform and only one species has not detected its distribution pattern, namely Ompok bimaculatus fish.The diversity and distribution of fish is strongly influenced by physical-chemical factors including current velocity, brightness, temperature, pH and dissolved oxygen.
index Pi: ni/ N ni: The number of individuals of fish of the type -i N: Total number of individuals of the whole type Criteria: H' < 1 : Low diversity H' 1-3 : Moderate diversity H' > 3 : High diversity The distribution pattern is calculated by Morisita index formula as follow: number of individuals in a total of n plots X 2 : Number of individuals on each plot -i Criteria : Id = 1, then the distribution is random Id <1, then the distribution is uniform Id >1, then the distribution is clustered

Table 2 .
Diversity indeks on the Lokop river.

Table 3 .
Fish distribution patterns in the Lokop River Description: Id = Morisita spread index, Ip = Standard degree of Morisita Discussion

Table 4 .
Measurement of environmental factors in the Lokop river.Quality standards for the maximum level of river water based on the Government Regulation of the Republic of Indonesia No.22 of 2021 for class II concerning Water Quality Treatment and Pollution *)