LIMNOLOGICAL CHARACTERISTICS AND CAGE CULTURE PRACTICE IN INDRASAROBAR RESERVOIR OF NEPAL Madhav K. Shrestha (IAAS, Chitwan, Nepal) Narayan P. Pandit (FDC, Hetauda, Nepal) World Aquaculture Conference 2008, May, Busan, South Korea

AquaFish CRSP USAID The Aquaculture CRSP is funded in part by United States Agency for International Development (USAID) Grant No. EPP-A The opinions expressed herein are those of the authors and do not necessarily reflect the views of the US Agency for International Development. ACKNOWLEDGEMENTS This research was funded by National Agricultural Research and Development Fund (NARDF), Nepal. All the funding for attending WAS ’08 was made by AquaFish CRSP.

Introduction Indrasarobar reservoir was built by damming in small river valley of mountain region of central Nepal. Indrasarobar reservoir was built by damming in small river valley of mountain region of central Nepal. Established in 1982 for hydropower generation. Established in 1982 for hydropower generation. Lies at the altitude of 1430 m from mean sea level (msl) at bottom. Lies at the altitude of 1430 m from mean sea level (msl) at bottom.

When filled it reaches 1530 m msl. When filled it reaches 1530 m msl. Reservoir is 7 km in length and m in width. Reservoir is 7 km in length and m in width. Total area is 216 ha when filled and 55 ha when dry. Total area is 216 ha when filled and 55 ha when dry. Introduction….

Water depth lowest 60 m and highest 100 m. Water depth lowest 60 m and highest 100 m. Reservoir is fed with seven small streams. Reservoir is fed with seven small streams. Filled during rainy season and draw down continuously till next rainy season occurs. Filled during rainy season and draw down continuously till next rainy season occurs. Introduction….

Started in 1988 Started in 1988 Technology copied from Phewa lake (Extensive system) Technology copied from Phewa lake (Extensive system) Fish Species: Fish Species: Silver carpSilver carp Bighead carpBighead carp Cage culture

Cage culture …… Cage size: Cage size: 5 m x 5 m x 2 m 50 m 3 ( in general) Stocking density: Stocking density: 10 fish/m 3 Feeding: Feeding: None

Cage Materials Bamboo poles for frame as well as for float Bamboo poles for frame as well as for float Recently plastic drum as floats Recently plastic drum as floats Nylon net Cage: Nylon net Cage: Nursery cage – 10 mm meshNursery cage – 10 mm mesh Grow out cage - 20 – 50 mm meshGrow out cage - 20 – 50 mm mesh

Cage culture expansion and production trend YearHouse- hold (no) Cage (no) (no)Cage Volume (m 3 ) Total prod n (mt)

Increased cage landing

Cage culture expansion trend

Cage productivity and Open water catch of reservoir Year Productivity in cage (kg/m 3 ) Open water Catch (mt)

Total cage fish production trend

Productivity trend of cage fish culture in reservoir

Trend of fish catch from reservoir

Limnological Characteristics of Reservoir ParameterMeanMaxMin Depth (m) Temperature ( 0 C) Dissolved oxygen (mg/L) pH Conductivity (μmhos/cm) Transparency (m) (Oct - Dec) 96 (Oct - Dec) 24.9 (Jul) 24.9 (Jul) 11.7 (Jun) 11.7 (Jun) 9.5 (Mar) 9.5 (Mar) 126 (May) 126 (May) 6 (Feb) 6 (Feb) 62 (May) 62 (May) 12.2 (Feb) 12.2 (Feb) 5.9 (Dec) 5.9 (Dec) 7.6 (Dec/Jan) 7.6 (Dec/Jan) 59 (Feb) 59 (Feb) 3 (Nov) 3 (Nov) Monthly mean and range of water quality parameters of reservoir during May 2006 to April 2007

Monthly mean water depth of the reservoir

Monthly water temperature during

Limnological Characteristics……. ParameterMeanMaxMin Total alkalinity (mg/L) Total suspended solids (mg/L) Total dissolved solids (mg/L) BOD 5 (mg/L) Chlorophyll-a (mg/m 3 ) (Mar) 65 (Mar) 980 (Aug) 382 (Aug) 5.6 (Dec) 5.6 (Dec) 20.7 (Sep) 50 (Sep) 48 (Sep) 45 (Sep) 3.7 (Aug) 2.7 (May)

Monthly mean chlorophyll-a during

Limnological Characteristics……. ParameterMeanMaxMin Total Nitrogen (mg/L) Total ammonium-N (mg/L) NO 2 -N (mg/L) NO 2 +NO 3 -N (mg/L) Total Phosphorus (mg/L) SRP (mg/L) (Aug) 0.15 (Aug) (Sep) (Jan) 0.22 (Dec) 0.06 (Dec) 0.56 (May) 0.04 (Feb) (Jun) (May) 0.06 (May) 0.02 (Feb)

Monthly mean total nitrogen (TN) and total phosphorus (TP) trend in reservoir during

Monthly mean total ammonium nitrogen (TAN) and soluble reactive phosphorus (SRP) content trend in reservoir during

Conclusion Increased cage landing has decreased productivity – Plankton limitation Increased cage landing has decreased productivity – Plankton limitation Mean fish harvest size has been decreased Mean fish harvest size has been decreased Current cage culture is about 4 ha which is about 2% area of the reservoir when fully filled and about 7% of the reservoir when lowest water level. Current cage culture is about 4 ha which is about 2% area of the reservoir when fully filled and about 7% of the reservoir when lowest water level.

Recommendation Options Decrease cage culture areaDecrease cage culture area Decrease stocking densityDecrease stocking density Introduce feeding system which will support non feeding cage culture system too.Introduce feeding system which will support non feeding cage culture system too.  Currently Government has chosen recommendation # 2 and has asked cage culture farmer to reduce stocking density by 50% (10 to 5/m 3 )