Diversity of Fish in Idanoi River and It’s Relationship to Physical Factors of Water Chemistry

. A river is an area through which a body of water moves from a high place to a low place either through the surface or underground which has an average width equal to or more than 5 meters. One of the rivers in Indonesia is the Idanoi river, located in the North Sumatra region, Ononamolo 1 Lot village, Gunungsitoli Selatan sub-district, Nias. This river is inseparable from human activities which affects the condition of river waters as a habitat for aquatic biota. The purpose of this study was to analyze the diversity of fish species in the river Idanoi and to analyze the physical-chemical factors of waters which correlate with the diversity of fish species in the river Idanoi. This study uses the Random sampling method. The results of the research obtained from the four research stations found 1 class, 5 orders, 7 families and 7 species. The highest density value was found at station 1 with a value of 0.023 ind / m2, fish diversity index ranged from 1.072 - 1.829 and the fish uniformity index ranged from 0.92 to 0.98. DO, BOD5 values and oxygen saturation correlated very strongly with fish diversity in river Idanoi village Ononamolo 1 Lot.

inseparable from human activities such as bathing, washing and leaving the house, garbage dumps such as household waste and tofu factory waste, where to dispose of animal waste and others.
Human activity in the Idanoi river greatly affects the condition of river waters as a water biota habitat.
Polluted river water conditions can interfere with life in the river. The entry of pollutants into rivers can alter the physical condition of environmental chemistry, thereby changing the diversity of water biota communities. The species contained in rivers are not all tolerant to the pressures of environmental conditions, but have tolerance limits [3].
In the waters there are groups of organisms that are intolerant and groups that are tolerant to contaminants. Organisms used as biological indicators in polluted waters are organisms that respond to little or no amount of contaminants. Intolerant organisms will experience a decrease in abundance and will even disappear from the aquatic environment. Intolerant organisms can be used as indicators of clean and normal water quality [4] . Fish is a key ecological factor related to the rules and functions of river ecosystems and also water biota that can be used as an indicator of the level of pollution that occurs in water. The diversity and abundance of fish in the river is influenced by environmental conditions, in addition fish also have a high enough economic value so that the surrounding population uses it for consumption needs by netting, fishing and electrocuting it. Sustainable fishing activities can result in reduced population and diversity of fish species, therefore research is needed to determine fish diversity and also the relationship of physical factors in aquatic chemistry with the presence of fish in the Idanoi river. Idanoi River is a river located in Ononamolo Village 1 Lot Of South Gunungsitoli Subdistrict, Nias is one of the rivers that have a diversity of fish species in it. Until now fish diversity data and its relationship to the physical-chemical factors of waters in rivers have never been studied so it is necessary to study data on fish diversity as a source of information.

Time and Location of Research
The study was conducted in May -December 2018. The research was conducted in Idanoi River Gunungsitoli Idanoi Subdistrict, Gunungsitoli City. The samples obtained were taken for identification to the Natural Resources and Environment Management Laboratory, Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Sumatera Utara, Medan.

Research Methods
Determination of the sampling location point in this study was done by purposive random sampling method, namely by determining 4 sampling stations. Each station is determined based on the activities in the area.

Station 1 research location
Station 1 is in Ononamolo Village 1 Lot, Hamlet 3, South Gunungsitoli Subdistrict. This station is a control area. At this station, no activity is carried out. The base substrates at this location are sand and rocks geographically located at 1o 12'41' N LU and 97o 39'32' BT.

Station 2 research location
Station 2 is in Ononamolo Village 1 Lot, Hamlet 3, South Gunungsitoli Subdistrict. Station 2 is an animal waste disposal area as well as household waste not far from the river stream. The base substrate of this location is sand, and the rocks are geographically located at 1o 13'34' N LU and 97o 39'42' BT.

Station research location 3
Station 3 is in Ononamolo Village 1 Lot, Hamlet 2, South Gunungsitoli Subdistrict. Station 3 is a tofu waste dump not far from the river stream. The base substrate of this location is sand and slightly muddy geographically located at 1o 13'20'' N Lu and 97° 39'28' BT

Station research location 4
Station 4 is in Ononamolo Village 1 Lot, Hamlet 1, South Gunungsitoli Subdistrict. This station is a sand dredging area. The basic substrate at this location is sand and stone geographically located at 1° 13'47' N LU and 97° 39' BT

Fish Sampling
Fish sampling using scattered nets was conducted at sampling points at each randomly selected research site. The spread of nets at one of the sampling sites was carried out as much as 45 times the spread of the net. The size of the spreader mesh used is 12.56 m2. Fish sampling is done in conjunction with measurements of aquatic chemical physical factors. The fish samples obtained were put in 10 kg of plastic and preserved using 70% alcohol to be further taken to the laboratory for identification using the identification book [5].

Temperature
Temperature measurements are done using a thermometer with a scale of 0 to 100°C. The thermometer is inserted into the body of water and leaves it for a while and then reads the thermometer scale and records the results listed on the thermometer scale.

Light intensity
The lux meter is placed at the research site after it is first turned on and sets the lux meter at an magnification of 200,000, then records the value listed on the screen.

Penetration of light
Measurement of light penetration is done using pieces of sechii, the way with pieces of sechii is put into river water until the piece of sechii is not visible then measured the length of the rope.

Speed of river currents
The ping pong ball is inserted into the body of the river along with the stopwatch, until it reaches a distance of 10 m. Then the stopwatch is turned off and the time is recorded. The current speed measurement is carried out as many as 5 reps.

Degrees of acidity (pH)
The measurement of the pH of water is done using a pH meter. The previous pH was calibrated to pH 7. The measurement of the pH of the water is done by way of the pH end of the meter inserted into the surface of the body of water and then reading the values listed on the pH meter and recording the results obtained.

Dissolved oxygen (DO)
Measurement of dissolved oxygen is done using the Winkler method, which is a sample of water inserted into a Winkler bottle, then adds 1 ml of MnSO 4 and KOH-KI respectively to the bottle and is homogenized. The sample is silenced briefly until a white deposit is formed, then added 1 ml of H 2SO4, homogeneous and silenced until brown deposits are formed. The sample is taken 100 ml and put into the erlenmeyer and then titrated with Na 2S2O3 0.0125 N to pale yellow, then the sample drips with 5 drops of amylase and is homogeneous until a blue solution is formed. Then the sample was titrated using Na 2S2O3 0.0125 N until the discoloration became apparent. The volume of Na2S2O3 0.0125 N used is calculated and the result is recorded.

Biochemical Oxygen Demand (BOD 5)
Bod5 measurements were taken after water samples were taken, incsessed for 5 days, then by the winkler method using chemical reagents MnSO 4 and KOH-KI, H2SO4, Na2S2O3 and amylase. Water samples are put into a Winkler bottle, then added 1 ml of MnSo4 and KOH-KI to their respective bottles and are homogeneous. The sample is silenced briefly until a white deposit is formed, then added 1 ml of H 2SO4, homogeneous and silenced until brown deposits are formed. The sample is taken 100 ml and put into the erlenmeyer and then titrated with Na 2S2O3 0.0125 N to pale yellow, then the sample drips with 5 drops of amylase and is homogeneous until a blue solution is formed. Then the sample was titrated using Na 2S2O3 0.0125 N until the discoloration became apparent. The volume of Na2S2O3 0.0125 N used is calculated and the result is recorded. The BOD 5 value is the initial DO value that is reduced to the final DO value.

Oxygen saturation
Oxygen saturation value (%) can be calculated using formula As follows: The concentration value corresponds to the temperature.

Nitrate levels (NO 3)
Water samples were taken as much as 5 ml, then added 1 ml of NaCl with volume pipette and added 5 ml H2SO4 75% then added 4 drops of Brucine Sulfate Sulfanic Acid. The solution formed is heated for 25 minutes. Then the solution is cooled and then measured with a spectrophotometer at λ = 410 nm. Then the values listed on the spectrophotometer.

Posfat Level (PO4)
A sample of water is taken as much as 5 ml and then added 1 ml of armstrong reagent and 1 ml of ascorbic acid. The solution is left for 20 minutes, then measured with a spectrophotometer at λ = 880 nm. Then the values listed on the spectrophotometer. Measurements of the overall physical factors of aquatic chemistry along with the units and tools used can be seen in Table 1.

Density, Relative Density and Frequency of Fish Presence
Based on Table 2 it can be seen that the type of fish that has the highest density is found at station 1, namely the species Homaloptera ripleyi which has a density of 0.008 ind / m 2 . This is because station 1 is an activity-free area that is a sandy and rocky area that allows Homaloptera ripleyi fish species to live in it. According to [8], this type of Homaloptera ripleyi fish is only found in rivers that have a lot of rocks upstream. Environmental conditions with very heavy currents cause this type of aquatic biota such as fish in these waters will have different physical characteristics and patterns of adaptation to fish that live in temperate or calm waters. According to [9], stating that one of the heavy current fish attached to river rocks such as homaloptera ripleyi species has an attractive body color that is a yellowish-black pattern on the dorsal so that it has the potential to be developed into ornamental fish. The lowest density values are at stations 3 and 4. The rare species found at station 3 are Homaloptera ripleyi while at station 4 the low species are Mugil cephalus and Clarias teijsmani. This is because in station 3 the substrate of the base is sandy and muddy so Homaloptera ripleyi is rarely found in distasiun. Homaloptera ripleyi is able to live in stone areas to protect itself from enemy threats, so the stones can be used as shelter. In station 4 it can be known that Mugil cephalus and Clarias teijsmani the lowest density value is 0.001 ind/m 2 . Every type of fish in order to live and breed properly must be able to adjust to the environmental conditions in which the fish live. The composition and distribution of fish is strongly influenced by physical, chemical, and biological changes. According to [10], changes in river habitat caused by humans can lead to limited distribution of fish. Some types of fish require different habitats at each stage of development such as catfish (Clarias sp.) which are isolated in one particular place and can also disrupt their life cycles leading to population decline.In table 2 it can be known that the type of fish that has the highest relative density value (KR) found at station 3 is Tor tambra with a value of 43.75%. If the KR value is more than 10% then it can be said that the type of tambra tor fish can live and thrive in areas where the substrate is sand and slightly muddy. According to [11], the habitat of tambra fish (Tor tambra) in general can be explained, namely the water base is generally in the form of rocks, gravel and sand substrate, clear water color, slow to heavy water currents, and the river environment is mostly primary forest.
According to [12], Cyprinidae are the largest family of freshwater fish, consisting of 220 genera and 2,420 species. The number of species of the family Cyprinidae indicates the ability of this family to adapt and multiply rapidly. The lowest relative density (KR) value at station 4 is Clarias tjeismanni with a value of 4.34%. Clarias tjeismanni is a freshwater fish species that can be tolerant to the environment of this species. The family Cyprinidae can live well in river areas that have strong currents and weak currents with good water quality. Cyprinidae are a family with a relatively large number of species in fresh water [13] but it can be known that at station 4 this rare type of catfish was discovered because station 4 is a station located adjacent to the mouth of the river. Catfish cannot survive in salt water because it so interferes with the osmotic pressure level of fluid in its body that the fish must make adjustments to its environment to survive. According to [14] that the ability of fish to survive at the maternity site depends on the ability to regulate body fluids so as to maintain a constant level of osmotic pressure and changes in salinity levels also affect the osmotic pressure of the fish's body fluids, therefore the fish must make adjustments or arrangements of internal osmotic work so that physiological processes in its body can work normally again. According to [15] the further the isoosmotic conditions, the higher the osmotic workload to balance the osmolarity pressure on the fish's body so that the energy wasted on osmotic performance becomes greater.

Diversity Index (Shannon-Wienner) (H') and Indices Uniformity (E)
The diversity index (Shannon-Wienner) and the fish uniformity index at each station on the Idanoi River can be seen in the following 4 table. The highest diversity index was at station 4 at 1,829. This is due to the good water conditions for the presence of fish and can survive due to the many food sources contained in these locations. According to [17], a community is said to have a high species diversity when there are many species with a relatively even number of individuals per species. In other words, that if a community consists of only a few species with an uneven number of individuals, then it has a low diversity. According to [4], a community is said to have a high species diversity when there are many species with an abundance of each species is high, whereas species diversity is low when there are only abundant species. Stations that have a low diversity index are found at stations 1. This is because station 4 is an activity-free area and environmental conditions whose vegetation does not support the growth of fish in the station. According to [18] explained that an increase in water temperature will increase the solubility of compounds in water. In toxic compounds, then the toxic strength of this compound generally increases with increasing temperature so that it can make the survival of the fish will be disrupted. Uniformity index (E) value on each station shown in table 4 ranges between 0.92-0.98 with the highest uniformity value found at station 3 of 0.98. The high uniformity value at station 2 is due to the presence of each type of fish in the waters is relatively evenly distributed. According to [19], the uniformity index value of fish species ranges from 0-1. The criteria for the uniformity value of fish species is the value of E is close to 0, then the spread of individuals between types is relatively unequal and it is found that there is a group of certain types of individuals that are abundant.

Abiotic environment
The measurement of physical-chemical factors in the waters of the Idanoi River can be seen in Table 5 follows.

Parameters of Physics
Based on Table 5 the measurable temperature at each station ranges from 25-30 °C. The highest temperature at station 1 is 30 °C. This variation is due to differences in the influence of dense vegetation around the waters. River. The temperature observed at each station is still ideal for fish growth. According to [20], fish sintasan increases with a steady increase in water temperature and reaches optimal conditions at stable temperatures between 29°C to 32°C. In these conditions, the entire physiological process of fish can run normally so that the vitality of the body can be maintained properly. According to [21], the optimal temperature range for organisms living in tropical waters is 20°C to 30°C.
Current speeds at each station range from 15-46 m/s. The current top speed is at station 1 which is 46 m/s. This is because station 4 is a sand dredging area. According to [22] states that the speed of currents is influenced by the slope, depth and width of the river. The range of currents obtained is generally found in tropical waters. According to [23], The highest light intensity is at station 1, which is 557 candela while the low intensity is at station 3 at 344 candela. This is due to differences in plant vegetation at each station. According to [17] states that if the intensity of sunlight is reduced then the process of photosynthesis will be inhibited so that oxygen in the water will be reduced.
The penetration of light measured at each station ranges from 0.5 m -1.5 m. The penetration of light distasiun 2, 3 and 4 1.5 m while at station 1 is 0.5 m. According to [24]states that the higher the depth of the disk the deeper the penetration of light into the water which will further increase the thickness of the productive water layer.

Chemical Parameters
Based on Table 5 the oxygen solubility (DO) values measured at each station range from 2.9 -5.2 mg/l. This value is still ideal for the growth rate of fish present at each station. According to [25] that A good DO value for fish growth is at 5 mg/l. It can be known that there are 3 stations whose oxygen solubility value is below 5 because the river conditions have been polluted so that it can cause a higher risk of death for fish life. A BOD value is the amount of oxygen needed by microorganisms to decompose organic compounds. Bod values that can be at each station range from 1.1 -5 mg / l this means that the condition of each station has been polluted. According to [26] that waters are categorized as unpolluted if BOD 5 ranges from 5 -10 mg/l. If at stations 2,3 and 4 the bod5 value is low this indicates that in these waters it contains compounds that are not biodegradable biological.
The pH measured at each station ranges from 6.8 to 7.5. The highest PH at station 4 with a pH of 7.5 while the lowest at station 2 with a pH of 6.8. Such pH conditions do not harm the organisms in it due to the normal pH state. According to [21] that most aquatic biota are sensitive to changes in pH and support pH 7-8.5. Highly acidic or highly alkaline river conditions will endanger the survival of the organism because it causes metabolic and respiration disorders.
Oxygen saturation at each station ranges from 38-64%. The highest oxygen saturation value is at station 1 which is 64% while the lowest oxygen saturation value is 38%. According to [27] that the higher the temperature of the water, the lower the level of saturation. Dissolved oxygen concentrations that are too low will cause fish and other aquatic animals that need oxygen to die.
Conversely, too high a concentration of dissolved oxygen also leads to a faster smelting process because oxygen binds to the hydrogen that coats the metal surface.

Pearson Correlation Analysis Values
Pearson Correlation Analysis was obtained by analyzing the relationship of diversity and physical-chemical factors of Idanoi river waters using the pearson method. The correlation index value (r) can be seen in the following table 6.  It plays a role in determining the presence of fish. Tolerance to high oxygen solubility in water has a major effect on the physiological activity of fish. If the solubility of oxygen is high then the growth of fish will be maximized. But in this case, if the DO is getting higher then the diversity of small fish and vice versa.
BOD values affect fish diversity because BOD still has a relationship with dissolved oxygen levels in water. Bod value will cause the amount of oxygen to be reduced so that the fish will lack oxygen for metabolic and respiration processes. The high value of BOD indicates that the amount of organic compounds found in water is also high. Fish can also utilize organic compounds for additional food. The presence of organic compounds can support the growth of plankton which is the main food of fish, especially fish that have small mouths.
Water temperature has a role in regulating aquatic life, especially in metabolic processes.
If the temperature is too high it will cause stress conditions in the fish that can cause death in the fish. In this case, when the temperature gets higher then the diversity of fish will be low n and vice versa.
Penetration of light also plays a role in determining the presence of fish. If the light penetration is high enough to reach the bottom of the water then the availability of oxygen to the bottom of the water is quite good. So that fish can be on the surface and underwater and cause various types of fish can live in every part of the water.
Oxygen saturation also determines the growth and diversity of fish. If the oxygen saturation condition is good or reaches 100% then the amount of dissolved oxygen reaches the maximum result which indicates that the water quality is good for fish growth.

Conclusion
The conclusions of this study are: a. Conclusions obtained from four research stations found as many as 1 class, 5 orders, 7 families and 7 species. The highest density values were found at station 1 with a value of 0.023 ind/m2, the fish diversity index ranged from 1.072 -1.829 and the fish uniformity index ranged from 0.92-0.98.
b. The values of DO, BOD5, temperature, penetration of light and nitrate (NO3-N) and oxygen saturation correlated strongly with the diversity of fish in the Idanoi river of ononamolo village of 1 Lot.