Results and Discussion

Ichthyofauna Diversity of Lakes

The present study records 18 species of ichthyofauna belonging to 4 orders, 7 families and 14 genera (Figure 9.2). The ichthyofauna belonging to order (Figure 9.3a) Cypriniformes were dominant in lakes (41 per cent) followed by Perciformes (33 per cent), Cyprinodontiformes (15 per cent) and Siluriformes (11 per cent).

The order Cypriniformes consists of species namely Catla catla, Labeo rohita, Ctenopharyngodon idella, Cyprinus carpio, Cirrhinus mrigala, Labeo fimbriatus, Puntius ticto and Hypophthalmichthys molitrix. Cyprinodontiformeswas represented by species such as Gambusia affinis and Poecilia reticulata. Perciformes was represented by Oreochromis mossambicus, Oreochromis niloticus, Channa punctata, Channa striata and Parambassis ranga. Siluriformeswas represented by Clarias gariepinus, Clarias batrachus and Heteropneustes fossilis. Similar results were observed in other lakes, for example, the order Cypriniformes were dominant in Mallasandralake of Tumakuru (Nayaka, 2018); Kelagerilake of Dharwad (Kamble and Ganesh, 2016) and Nagaram tank (Ramulu and Benarjee, 2013).

Fish species belonged to 7 families (Figure 9.3b) namely, Ambassidae, Channidae, Cichlidae, Clariidae, Cyprinidae, Heteropneustidae and Poeciliidae. Among these, Cyprinidae was dominated in 41 per cent of monitored lakes, followed by Cichlidae (28 per cent), Poeciliidae (15 per cent), Clariidae (9 per cent), Channidae (3 per cent), Ambassidae (1 per cent) and Heteropneustidae (1 per cent).

Cyprinus carpio, Ctenopharyngodon idella, Gambusia affinis, Oreochromis sp., Clariasgarie pinus and Hypophthalmichthys molitrix are exotic fishes recorded in the current study. Clarias gariepinus is a hardy species and can tolerate both oxygenated as well as poorly oxygenated waterbodies (Ogundiran et al., 2010).

Table 9.1: Ichthyofauna Diversity in Lakes of Bangalore, Karnataka

Ichthyofauna Diversity in Relation to Water Quality of Lakes of Bangalore

Gambusia affinis and Poecilia reticulata feed on larvae and is used for mosquito control (Mahapatra et al., 2014). The invasion of exotic species results in loss of native and endemic species (Singh et al., 2013; Sandilyan, 2016). Exotic fish species were introduced in India for aquaculture, aquarium, sport fishing, weed control, etc. and the introduction of exotic species led to the decline in native species of fish and biodiversity (Kumar, 2000).

Among the 14 genera, Catla was found in 32 lakes and Oreochromis was recorded in 29 lakes in the current investigation (Figures 9.4 and 9.5). Based on the diet (Table 9.2), fishes are grouped as herbivorous, omnivorous, larvivorous, planktivorous and carnivorous. For example, Labeo rohita (column and bottom feeder) prefers plant material and decaying vegetation. Catla catla (surface feeder) feed mainly on phytoplankton whereas Cirrhinus mrigala (bottom-feeder) feed mainly on decaying vegetation (Chattopadhyay, 2017). Oreochromis niloticus are opportunistic feeders and feed on detritus, phytoplankton, crustacean, aquatic Ichthyofauna Diversity in Relation to Water Quality of Lakes of Bangalore insects, small fish, zooplankton and macrophytes (Mohamed and Al-Wan, 2020; Chatterjee et al., 2015).Under conservation status as per IUCN (2010),one species was categorized as critically endangered, one species under near threatened, 13 under least concern and one species under vulnerable category (Table 9.2).

Table 9.2: List of Ichthyofauna, their IUCN Status, Diet Pattern and their Benefits

*LC: Least Concern; NE: Not Evaluated; CR: Critically Endangered; NT: Near Threatened; VU: Vulnerable.

Indian major carps such as Catla catla, Cirrhinus mrigala and Labeo rohita contribute 70 to 75 per cent of the total freshwater fish production and have high economic importance (Jayasankar, 2018). Genus such as Clarias, Channa and Heteropneustes are air breathing fishes with good market value for live fish (Thirumala et al., 2011).Dishes prepared with fish flour (of Oreochromis niloticus) are rich in proteins, lipids, essential amino acids, ash and polyunsaturated fatty acids (PUFAs) (Alam and Aslam, 2020), which highlights the need to conserve fish fauna to sustain food and medicine to the dependent population.

Water Quality of Lakes

Health of aquatic ecosystems are assessed based on water quality considering the physical, chemical and biological characteristics of water. Evaluation of these parameters will aid in understanding the suitability of lake water for biotic consumption and health of a particular aquatic ecosystem. Fish is very sensitive to variations in water quality and hence considered as biological indicator in aquatic ecosystems. Thus, it is necessary to understand the water quality of lakes or habitat conditions of fishes. Physical, chemical and biological parameters assessed in sampled lakes are discussed next.

Water Temperature and pH

Water temperature influences both the physico-chemical variables and biological activities in the aquatic ecosystems. Temperature affects the microbial (algae and bacteria) activities in water as it influences the organic matter decomposition and nutrient cycling. Temperature also affects the solubility of gases like O₂, CO₂ and NH₃ (Siriwardana et al., 2019). Water temperature in the current study varied between 23.5oC to 34.2oC (Figure 9.6). pH varied among the monitored lakes and found to range between 7.2 to 10.19, indicated an alkaline nature of lake water (Figure 9.6).

pH regulates many biological processes and biochemical reactions. In case of pH, the desirable range for fish culture is 6.5 - 9.0. Doddakallasandra had high levels of pH among all the lakes due to high photosynthetic activities by phytoplankton. The photosynthesis raises the pH whereas respiration and decomposition processes lowers pH in lake water. Fish have an average blood pH of 7.4, so the acceptable range for fish culture would be 6.5 - 9.0. The pH in water ranging from 4.0 - 6.5 and 9.0 - 11.0 is stressful for fish growth and reproduction. Fish death can occur at pH level of <4 or>11 (Ekubo and Abowei, 2011).

Total Dissolved Solids (TDS) and Electrical Conductivity (EC)

Total dissolved solids in natural waters are mainly contributed by the presence of carbonates, bicarbonates, sulphates, chlorides, phosphates and nitrates of magnesium, calcium, sodium, potassium, iron etc. and tiny amounts of organic matter (Ramachandra et al., 2014). Electrical conductivity gives the measure of the capacity of water to conduct an electric current. When the concentration of dissolved ions in water increases then, electrical conductivity also increases. The value of total dissolved solids and electrical conductivity in lakes ranged from 152.5 mg/L to 1548 mg/L and 306.67µS/cm to 2814 µS/cm, respectively (Figure 9.7). Lakes such as Basapura-1 and Basapura-2 had higher ionic contents with higher TDS and EC levels. The increased levels of dissolved and suspended solids will decrease the dissolved oxygen levels in aquatic ecosystems (Yýlmaz et al., 2020). The optimum conductivity level for fish culture differs among different species as they vary in their capability to maintain osmotic pressure (Kumar et al., 2017).

Turbidity and Dissolved Oxygen (DO)

Turbidity occurs due to the presence of various suspended and colloidal matter in lake water such as clay, silt, inorganic matter, organic matter, plankton and tiny micro-organisms (Ramachandra et al., 2018). Turbidity in monitored lakes was found to range between10.14 NTU - 306.33 NTU (Figure 9.8) .High turbidity in lakes result in low light penetration to bottom levels, reduces photosynthetic rate and may even cause fish death due to clogging of gills (Saraswathy et al., 2015). The concentration of dissolved oxygen in lake water varies with temperature, amount of organic waste, sediment quality/quantity, turbulence, photosynthetic rate and respiration/decomposition (Devi et al., 2015). The solubility of dissolved oxygen decreases under low atmospheric pressure and high saline conditions (Rouse, 1979). The dissolved oxygen levels ranged between 1.52 mg/L - 11.27 mg/L in lakes with minimum value in Gangadharkere while maximum value in Jakkur lake (Figure 9.8).

Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD)

Biochemical oxygen demand is the amount of oxygen utilized by micro- organisms in stabilizing the organic matter (Davraz et al., 2019). The chemical oxygen demand is the amount of oxygen equivalent of the organic matter in lakeIchthyofauna Diversity in Relation to Water Quality of Lakes of Bangalore

Biodiversity Challenges: A Way Forward

water that is susceptible to oxidation with the help of a strong chemical oxidant. The BOD and COD of lake water samples ranged between 7.45 mg/L - 99.59 mg/L and 11.33 mg/L - 150 mg/L, respectively (Figure 9.9). Both BOD and COD of lake water increases with an increase in the organic matter content due to organic pollution from point as well as non-point sources.

Total Alkalinity and Chloride

Total alkalinity provides the measure of the ability of water to neutralize acids. Alkalinity is due to the presence of carbonates, bicarbonates and hydroxides of calcium, magnesium, potassium, sodium and salts of borates, silicates, phosphates, etc. (Sarkar et al., 2020, Qureshimatva et al., 2015). The salts of sodium (NaCl), potassium (KCl) and calcium (CaCl₂) contribute chlorides in lake water. The total alkalinity and chloride in sampled lakes were recorded as 81.33 mg/L - 684.33mg/L and 25.56 mg/L - 1165.82 mg/L, respectively (Figure 9.10). The desired level of alkalinity for fish culture is between 50-150 mg/L whereas the desirable level of chlorides for catfish production is > 60 mg/L (Rajbongshi et al., 2016). The main source of chloride in lake water include salt deposits, untreated sewage, industrial effluents and through agricultural inputs (Sajeev et al., 2020).

Total Hardness, Calcium and Magnesium

Total hardness is caused due to the presence of cations and anions such as calcium and magnesium, carbonates, bicarbonates and chloride in lake water (Kamboj and Kamboj, 2019). Calcium levels in water help in osmoregulation under stressful conditions and are important for egg and larvae development in fishes. A calcium concentration of >400 mg/L is detrimental to fish and crustaceans (Stone et al., 2013). Magnesium generally occurs in lesser concentrations than calcium in lakes. The total hardness ranged between 72 mg/L – 510 mg/L in sampled lakes. Calcium and magnesium are necessary for metabolic activities like bone and scale formation in fishes (Bhatnagar and Devi, 2013). A hardness level of 150 mg/L is recommended for the optimum growth and survival of Labeo rohita (Rajkumar et al., 2018). The calcium and magnesium varied among lakes and recorded as 14.43 mg/L - 160.32 mg/L and 3.72 mg/L - 42.41 mg/L, respectively (Figure 9.11).

Nitrate and Ortho-phosphate

Nitrate and phosphate are the limiting nutrients in aquatic ecosystem. Nitrate ranged between 0.118 mg/L - 4.283 mg/L among lakes of Bangalore (Figure 9.12).

The increased levels of nitrogen and phosphorus in water occurs due to the discharge of untreated domestic wastes, industrial effluents and agricultural runoff (Pinto et al., 2020). In the present study, ortho-phosphate ranged between 0.06 mg/L - 4.41 mg/L (Figure 9.12). The increase of phosphorus levels in freshwater are due to domestic, agricultural and industrial inputs (external P loading) along with internal P loading from the bottom sediments (Calijuri et al., 2002). The extensive use of detergents and sewage are the major sources of phosphates in lake

Biodiversity Challenges: A Way Forward

Biodiversity Challenges: A Way Forward

water (Abdusalam et al., 2019). Water rich in phosphorus favors the growth and proliferation of algae, which results in the eutrophication in water bodies (Rocha et al., 2015). Detergent effluents can induce several toxicological effects in Clarias gariepinus (Ogundiran et al., 2010; Nkpondion et al., 2016).

Factors Affecting Lake Water Quality

Principal component analysis (PCA) was applied to the normalized data sets (i.e., 15 physico-chemical parameters of 36 lakes) to identify underlying factors affecting water quality of lakes. The PC loadings of > 0.75, 0.75 - 0.50 and 0.50 - 0.30 were classified as ‘strong’, ‘moderate’ and ‘weak’ respectively (Liu et al., 2003). The principal components (PCs) with eigenvalues greater than one (>1) were considered significant to explain the whole dataset.

In the present study, four principal components were obtained with eigenvalues greater than 1, that explained 81.4 per cent of the total variance in the water quality dataset (Table 9.3). The first component, PC1 accounted for about 47.5 per cent of the total variance in the water quality data set. PC1 has positive loadings on water temperature (0.50), TDS (0.94), EC (0.97), total hardness (0.90), calcium (0.93), magnesium (0.53), chloride (0.88), turbidity (0.76), BOD (0.83) and COD (0.76). This factor is attributed to ionic and organic pollutants, which highlights of industrial and domestic discharges.

Table 9.3: Loadings of Environmental Variables on Principal Components for Water Quality Datasets

PC2 accounted for about 18.0 per cent of the total variance with positive loadings of water temperature (0.52), pH (0.57), nitrate (0.58) and DO (0.51) and negative loadings of magnesium (-0.62) and alkalinity (-0.73). This factor corresponds to organic pollution and relates to the productivity of freshwater ecosystem. The PC3 explained 8.7 per cent of the total variance with positive loadings of ortho- phosphate (0.53), nitrate (0.53) and pH (0.61). This factor represents the varied sources of nutrient pollution due to domestic sources, agricultural activities (fertilizer input), industrial discharges and urbanization (urban wastewater). PC4 explained 7.2 per cent of the total variance and is related to DO (0.73) which suggests that lakes had enough amount of dissolved oxygen to sustain aquatic life. A healthy aquatic ecosystem holds DO level of 4 - 6 mg/L (Avvannavar and Shrihari, 2008). DO varies with time, season, rate of photosynthesis, decomposition and respiration activities in lake water. The untreated sewage flowing into lakes alters water chemistry by increasing the ionic, organic and nutrient contents.

WQI Status of Lakes in Bangalore

WQI is computed considering ten water quality parameters - pH, electrical conductivity, total dissolved solids, dissolved oxygen, total hardness, calcium, magnesium, chloride, total alkalinity and nitrate. The water quality condition is described on the basis of WQI value in the range of 0-25, 26-50, 51-75, 76-100 and >100 which corresponds to excellent, good, poor, very poor and unsuitable respectively. Overall, Water quality index (WQI) for the lake water samples were found in the range of 38 to 122 (Figure 9.13).

In the current study on lakes of Bangalore, about 5 per cent of lakes (Lalbagh and Yediyur) fell under good category while 31 per cent lakes fell under poor category. Majority of lakes (about 56 per cent) were classified under very poor category. Lakes namely Basavanapura, Mallathahalli and Sheelavanthakere which fell under the category of unsuitable (8 per cent), is not appropriate for fish culture. The water quality of lakes is deteriorating as evident from WQI status of lakes, mainly due to the inflow of sewage water from residential and commercial complexes, agricultural run-off, anthropogenic activities, untreated effluents from industries and factories, dumping of solid wastes into lakes and lack of proper sanitation.

In earlier studies, WQI values of Sankey tank water belonged to good water class whereas Mallathahallilake fell under poor water category (Ravikumar et al., 2013). WQI values of Hebballake fell under very poor category (Sudarshan et al., 2019). Earlier study has reported WQI of 3 lakes in Haryana of > 100, indicating that water is unsuitable for drinking, outdoor bathing and other uses (Kumar et al., 2018). WQI status of Pariyejlake is poor and unfit for human consumption (Thakor et al., 2011). Anthropogenic stress caused the deterioration of water quality of Dal lake as evident from WQI i.e., polluted and unfit for human consumption (Ahmad et al., 2020).

Water quality parameters such as temperature, suspended solids, pH, DO, ammonia, nitrite, carbon-dioxide and alkalinity play a crucial role in the growth, reproduction and survival of fish (Okoliegbe et al., 2020). The diversity and distribution of ichthyofaunais governed by pH, turbidity and electrical conductivity (Shetty et al., 2015). The climate change with a decline in rainfall and delayed monsoon, affects temperature of freshwater ecosystems and the breeding behavior/ ecology of fishes (Ninawe et al., 2018). The growth rate of Oreochromis niloticus increased at higher temperature and DO whereas the growth rate declined under increased pH, conductivity and ammonia levels (Makori et al., 2017). The sewage and industrial effluents let into water bodies increases the levels of total suspended solids, total dissolved solids, COD and BOD (Ramanujam et al., 2014). The detergent effluents in lake water induce severe damage to gills, skin, kidney, heart, liver and brain of fish (Nkpondion et al., 2016).Inorganic pollution from industries is another main threat to ichthyofauna (Rao et al., 2014). The waterdepth, pressure, turbulence, temperature, light and turbidity are important for fish culture (Priyamvada et al., 2013), which necessitates maintaining water quality to sustain fish production.

In 1970s, about 55 fish species were recorded in Bangalore. At present, there is a massive reduction in ichthyofauna diversity in Bangalore as the lakes are under threat due to water pollution,urbanization, encroachment of lakes, habitat loss or habitat degradation, invasion of exotic species, agricultural practices, climate change,flood, drought, over-harvesting of fish resources and loss of interconnectivity among lakes. The anthropogenic activities, water pollution, eutrophication, habitat degradation, overexploitation, hydrologic alterations, flow modification, damconstruction and climate change are the major threats to fish biodiversity (Borah and Das, 2020; Bhakta et al., 2019; Gupta et al., 2015; Vijaylaxmi et al., 2010). Introduction of exotic species and adopting destructive fishing method such as dynamite or poisoning would cause serious threat to native ichthyofauna (Bose et al., 2019). Urbanization, pollution and water abstraction for irrigation and power generation impose threat to fish diversity (Kumar Sarkar et al., 2013). Hence, it is essential to regulate the sustained inflow of untreated sewage and industrial effluents into lakes to maintain the integrity of aquatic ecosystems and sustain fish diversity. The nutrient removal in lakes (bioremediation) can be achieved in a cost effective way through the integration of conventional water treatment methods with the constructed wetlands (macrophytes) and algal pond (Ramachandra et al., 2018).In order to increase the ichthyofauna diversity, there is a need to avoid habitat destruction, control pollution sources, should ban the introduction of invasive species, harvesting of fish during the spawning period and the harvesting of juveniles. Environmental awareness through awareness programs would help in educating public on the impacts of water pollution on freshwater fish and also the role of healthy ecosystem in supporting people’s livelihood. Regular workshops and awareness programs on wetland goods and services would also help in the conservation of aquatic biodiversity.