Abstract

Biodiversity of an aquatic ecosystem and its management is considered to be one of the leading concerns of enabling sustainable use of natural resources. Fishes have a wide impact on the existence and influence on other organisms in their habitat. In the present study of fish diversity and its abundance in Nakki Lake, Mount Abu was studied in the weather cycle of 2018-19 in ten different sampling sites. The findings show the precise number of fish, population density, homogeneity and species dispersion patterns in Nakki Lake. To estimate the number of fish population in the lake, quadrat sampling method was used owing to certain constraints by the department of forest, as Mount Abu falls under the categoriy of eco-senstive zone. The lake supports around twelve species of fishes which are Aorichthys seenghala, Mystus cavasius, Carassius auratus, Catla catla, Cirrhinus cirrhinus, Garra gotyla, Labeo gonius, Labeo rohita, Puntius sarana, Puntius ticto, Gambusia affinis and Heteropneustes fossilis. Out of these dominating fishes are Labeo gonius, Labeo rohita, Catla catla, Heteropneustes fossilis. The result shows that the lake supports fish diversity and the lake habitat is condusive to the growth of thriving population of fish as well as other aquatic species. The other method such as electrofishing could not be carried out since the lake is leased for boating facilities for tourists and fetches high renumeration, which contributes to the revenue of the town.

1. Introduction

Nakki Lake is considered to be an attractive tourist spot and is the biggest water reservoir of Mount Abu, a small hill station in Rajasthan. The lake is known for its unique beauty as it is surrounded by the Aravali hills on all sides. It fulfils the annual need of drinking water and other needs of the tourists, residents as well as the endemic species of the habitat. Fishes play a symbolic role in fresh and marine water ecosystem. It controls the population of zooplankton, phytoplankton by consuming them as food, and serve as prey for higher trophic level animals and humans in an ecosystem. It is uncertain to crosscheck the accuracy of the fish population, unless fishes have been stocked in reservoirs with known numbers, or fishes are counted directly by draining out from the water body ^{1, 2, 3}. A particular fish species may have colonies, periodic, occasional or seasonal movements, or other ethological patterns which effect susceptibility in sampling.

Thomas (1994) suggested that alteration in habitat and destruction is the major cause of extinction of most freshwater fishes. Fish communities vary with different freshwater lake systems; hence site-specific management is important in fish biodiversity conservation ^{4, 5}. Guisan and Thuiller (2005) assume that the characteristics of distribution of fish species and habitat emerges from combination of biotic and abiotic valuables or either anyone or some of them ^{6, 7}. Rosenfeld (2003) and Ahmadi-Nedushan et al., (2006) confirm that abiotic features are often defined essentials of fish habitats in water ecosystem that are fundamentals for the survival and flourish of population or individuals ^{8, 9}. According to Elith and Leathwick, (2009) very few fish territory models exceptionally comprise biotic factors, which can be used to infer interactions between species. Quadrat sampling method mainly deals with precision, the précised counting of fish population with multiple sampling in different locations in a specific habitat. Gothwal and Gupta (2018) studied the icthyofauna in Sant-Sarover pond, Mount Abu, India, their finding suggested that the fish population in Sant-Sarover pond had the ability to reduce eutrophication. The variations in the rate of pH also affects the growth rate of icthyofauna in Sant-Sarover pond ¹⁰.

2. Materials and Methods

Nakki Lake (Mount Abu) was selected for research purpose, replete by annual rainfall. It is situated at the highest peak of Aravali range “Mount Abu” (Arbudanchal), Rajasthan. The Aravali range is composed of igneous rocks (Granite and Basalt) and known as the oldest mountain ranges in the world ^{10, 11, 12}. The Aravali hill range, running from north-east to south-west, divides the state into western arid and eastern semiarid regions (Anon. 2009). The total surface area of Nakki-Lake is 209,776.1m² (Figure 1) identified by GIS tool.

Ÿ Location: 24.596140°N, 72.703066°E

Ÿ City: Mount Abu

Ÿ State: Rajasthan

Ÿ Country: India

Ÿ Max. Depth: 70-80 ft.

A quadrat can be made by staking out typically a square area of the same size by using string or sticks of metal, wood or plastic. A specific size quadrat was used to determine population abundance and density. Each quadrat marked off a square area of 10 X 10 meter encompassed by fish net within the habitat. After setting up quadrat, the numbers of fish samples within the boundary were counted. Multiple quadrat samples were performed throughout the habitat at several random locations, which ensured that the numbers recorded were representative of the habitat overall. The data was used to estimate the population size and population density within the entire habitat. Sokal and Rohlf (1981) studied that a biased but sensitive scale might yield inaccurate but precise weight. By chance, an insensitive scale might result in an accurate reading, which would however be imprecise, since a repeated measurement would be unlikely to yield an equally accurate weight, as the measurements are impartial, precision will lead to accuracy ^{13, 14, 15}.

Quadrat sampling method was used to identify the fish population. The total surface area of the lake is 209,776.1m² identified by GIS tool (Figure 1). On the basis of the topography and the concentration of human contact with the lake, it was categorised into three specific regions. Each region was also categorised into three specific sites and one site taken from the central region of Nakki Lake. In order to calculate total fish population of Nakki Lake, ten sampling sites (Figure 2) were identified which are as follow:

1. Populated Region (Site-1, Site-2, Site-3)

2. Non-Populated Region (Site-1, Site-2, Site-3)

3. Mountain Region (Site-1, Site-2, Site-3)

4. Central Region

Further, fish samples were collected from ten pre-selected sampling sites of populated, non-populated, mountain and central regions of the lake and their data was calculated to gauge the precise fish population, population density and homogeneity of fishes in Nakki Lake.

3. Result and Discussion

The total no. of fishes counted in Nakki Lake was 299,769.89 among which the population of small fishes were 264,947.08, whereas the population of large fishes were 34822.81. As shown in (Table 1), it can be concluded that the total number of small and large fishes observed in quadrat sampling of three sites of populated region is 517 and 71, however the number of fishes found in quadrat sampling of non-populated and mountain region are 329 and 42, 295 and 34 ^{16, 17, 18}.

The comparative analysis of fish population density in Nakki Lake, Mount Abu indicates that the highest fish’s population is found in the populated region (Figure 6, high density human population zone). In this zone there is continuous supply of food such as flour balls, popcorns and bread, hence fish species as well as ducks swim mostly in this region. Icthyofauna in Nakki Lake includes 10 to 12 different species of small common carps and large fishes ^{19, 20}. Considering the Null hypothesis for the homogeneity in fish population (Table 3), calculated value of Chi-Square (χ2) was 139.06 for 9 degree of freedom at 5% level of significance. Tabulated value of Chi-Square (χ2) was 16.91 for 9 degree of freedom at 5% level of significance. The calculated Chi-Square value (χ2) was more than the tabulated Chi-Square value (χ2), hence it does not accept null hypothesis (H_o).

a) Total area of Nakki Lake (Figure 1) = 209,776.1 m²

b) Size of the quadrat selected is of 10 x 10 meter = 100m²

c) Total number of quadrat counts available in Nakki Lake = 209,776/100 = 2097.76

Sample mean () represents an estimate of the true population mean (μ).

Where:-

x_i = Total sample observation of individuals

n = Total sample size (number of plots) = 10

On the behalf of Table 1:-

(A) The total number of Small fishes in sampling observation is 1263. Total sample size (number of plots) = 10

(1)

(B) The total number of Large fishes in sampling observation is 166. Total sample size (number of plots) = 10

(2)

Hence, from (1) and (2), the total no. of précised fish population calculated in Nakki Lake was 264,947.08 + 34822.81= 299,769.89.

In the given sampling of fish population from Table 1:-

Null hypothesis (H₀): Population of small and large fishes are homogenous.

Alternative hypothesis (H_A): Population of small and large fishes are not homogenous.

4. Conclusion

The study of fish population with quadrat sampling method indicates that the total no. of fishes observed in Nakki Lake was 299,769.89 which includes the population of small and large fishes are 264,947.08 and 34822.81. The comparative analysis of all sampling sites indicates that, small fishes are widely distributed in all regions (Figure 4 & Figure 5), as they mostly feed on planktons and algae which are available on surface of rocks in the mountain region, which acquires a small habitat for fish colonies. Species dispersion patterns or distribution pattern indicates the type of dispersion of individuals in that habitat. The dispersion of fish individuals in Nakki Lake appears to be random dispersion, as the individuals were distributed or dispersed randomly without any foreseeable arrangement.

Icthyofauna in Nakki Lake includes 10 to 12 different species of small common carps and large fishes (Figure 3), (Table 2). The migration of fishes in the winter season was less compared to summer and rainy season, as the air temperature of Mount Abu in winter varies from -3 to 9°C, hence fish species remained at deep water instead of migrating to surface. In summer and rainy season the fish species are abundantly available in populated region compared to other regions. The test of homogeneity does not accept null hypothesis. As the calculated Chi-Square value (χ2) 139.06 is more than the tabulated value of Chi-Square (χ2) 16.91 for 5% level of significance at 9 degree of freedom.

Acknowledgments

This manuscript was developed as part of my Ph.D project “Limnology and Ecological Diversity of Nakki Lake, Mount Abu (Rajasthan) India. I am extremely thankful to Madhav University (Department of Bio-Science) for providing research facilities to conduct the demographic study. I am thankful to the local boatmen of Nakki Lake, Mount Abu for their outright support to conduct this research.

References