Effect of Introduction: The data on seeding (refer Table 1) reveals that no scientific approach is adopted while seeding. Without determining the carrying capacity and productivity of the reservoir enormous amount of seeds were introduced during the early 90s. In the absence of any baseline data on fisheries, it is hard to quantify the impact due to improper introduction. Even then by looking at the present condition it becomes clear that it has negatively affected the total fish fauna.

Introduction of Tilapia (Oreachramis masambica): This is slowly gaining its phase in Linganamakki reservoir. As per the local fishermen, the catch of Tilapia is increasing over the years. The catch starts at the post monsoon period and during November, it dominates the entire catch. Due to the least demand for this fish in local markets, fishermen treat this fish as an unwanted catch. Scientifically, this fish is regarded as a hardy, territorial and a powerful competitor in nature. Ecologically, these fishes have adverse effect on the fish diversity. As per the fishermen, the maximum weight that this fish can attain is 0.5kg in this reservoir.

Endangered Mahseers: Tor Khudree and Tor mussullah are the two species present in the reservoir. These fishes breed during post monsoon period and their habitat is rocky pools. Presently, mahseers are endangered in the Indian context. Their commercial value and habitat destruction might be the major factors. In the Linganamakki Reservoir, mahseers were recorded in Hallibylu of Sharavathi Wildlife sanctuary area. In other areas also these fishes are rarely found. These fishes prefer rocky bottom areas with optimum temperature. In the present condition, the silt deposition at the bottom of the reservoir is slowly disturbing their habitat along with the fishing pressure.

Cyprinus carpio (Common carp) fishery: During monsoon period, common carp is the major fish catch in deeper areas like Holebagilu, Madenur and Hasaramakki areas. During other seasons, this fish catch almost reduces to zero. Since, Common carp is a bottom dweller, high transparency of the reservoir makes it to move to the bottom surface. During monsoon season, the transparency reduces and common carp comes to the water surface. Cyprinus carpio is regarded as one of the major competitors to native species of fishes for food and habitat. In the present case, this fish may affect benthic fishes like Wallago attu, Ompok bimaculatus and Channa marulius indirectly. Growth is quite fast in Cyprinus carpio and it consumes the lower level organisms like phytoplankton and other aquatic insects. The decrease in population of these lower level organisms due to continuous feeding by common carp may affect the population of other fishes with similar food habits. The decrease in such fishes may in turn affect the food requirement of carnivorous fishes and result in decrease in their population.

Diseases: Fishermen recall the widespread out break of a Epizootic Ulcerative Syndrome (EUS) decease about 5 years back, featured by sever ulcerative skin lesions, which ultimately caused the death of the fish. Reports on out break of EU in Shimoga district show that during Dec 1993 - Jan 1994 the disease had caused mortality in the major and minor irriagation tanks. Even though the disease affected the bottom dwellers like Channa spp., minor carps and catfish, interestingly, it has not affected the Indian major carps like Catla, Rohu, Mrigal and common carp in Kamataka (Mohan and Shankar, 1994). This disease might be one of the main reasons for extinction of many species. According to the local fishermen, fish species like Wallago attu, Heteropneustes fossilis and Channa marulius were severely affected by this disease and there is a remarkable decline in their population. Presently, there are no reported episodes of this disease outbreak in the reservoir. Still, sampling at Lingadakai found one sample of Garra gotyla stenorynchus with such lesions on the body.

Mastacembelus armatus: Recently, another parasitic infection to the species mastacembelus armatus was observed in areas like Hasaramakki. The infection showed mumerous lesions within the abdomen with approximate diameter of 1-2 cm. After the death of the fish during fishing, nearly 2 inch long thread like worms were penetrating out of the abdomen. With the present available information, it can be concluded that the fish is acting as a host for those parasites, which are in a stage of completing their life cycle. Since, there were no deaths of the diseased fishes, it further justifies the argument. The infection was at its peak during the summer season and affected almost all the fishes of the species. During this period, the commercial use of this fish had almost stopped in this area. However, the suitability of the fish as food and the reason for the first time occurrence during June 2002 remain unanswered.

Destruction at the breeding ground: Species of Garra, Puntius, Labeo, Cirrhinus, Mystus, and Pseudeutropius etc. are regarded as resident species. These fishes breed within the reservoir or migrate to smaller distance in search of shallow weedy areas for breeding. Most of the people residing along the bank go for fishing during the monsoon season. This is the season when a large quantum of fish can be caught. These people use traditional techniques to capture these fishes. These are the localities where large congregations of the spawning fishes are caught and destroyed. Even some fisherman move to shallow upstream areas during monsoon to ex­ploit the breeding grounds. Probably this is a prime factor that retards the population of these migratory fishes. Most of the streams along the western side are observed to be excellent breeding grounds for the native fishes.

Over exploitation and improper fishing system : The over exploitation of the reservoir plays a major role in extinction of the species. The department deliberately issues the license to any number of fishermen. Many fishermen from Tungabhadra dam migrate to this area during rainy season and catch huge quantity of fish. This has adversely affected the livelihood of permanent local fishermen. Over exploitation of the reservoir for fishing has resulted in excessive mortality and reduction in effective population size of the fish. Monsoon is the breeding season for most of the fishes and the fishing activity is at its peak during this season.