Assessment of cage culture and its effect on Maphou Reservoir, Manipur

Kamei Ringjonmeilu / P Bhattacharjee / Y Bedajit / Ch Basudha / J Parhi / P Pal / MK Datta *

Among the top 5 States in terms of fish consumption, Manipur stamds in 3rd place with an annual consumption rate of 14.1 kg per capita per year. However, the State’s production is about 32,000 tonnes a year-1 against the requirement of 52,000 tonnes year-1 (Anon. 2020).

In order to make the State self-sufficient in terms of production, proper management and developmental activities should be considered. And cage culture in the Maphou reservoir which is situated on the Thoubal river, Manipur, can be considered as one of the initiatives as many of the villagers who are residing on the periphery of the reservoir lost their livelihoods due to damming.

Since, cage culture is suitable for a wide range of open freshwater ecosystems especially reservoirs and lakes, to augment the production of the region as well as to uplift the livelihood. But there is a gap in knowledge about the production potential of the reservoir and the effect on cage culture on its environment. It is essential to investigate the physico-chemical characteristics and productivity of the reservoirs.

Therefore, the present work was undertaken by Kamei Ringjonmeilu, Post Graduate Scholar under the Department of Fisheries Resource Management, College of Fisheries, Lembucherra, Tripura, Central Agricultural University, Imphal to study the variation of the different water quality parameters and the primary productivity of the cages installed in the Maphou reservoir was estimated.

It was observed that the cage culture carried out in the reservoir was a semi-intensive type of manage- ment. Fish were not stocked at the optimum stocking density and feeding was done in a sustenance way. Species stocked in the cages were Silver carp, Grass carp, Tilapia, Jayanti Rohu, Pangasius, and Vietnam koi. Water quality parameters showed spatiotemporal variation during the study period.

The water's temperature ranged from 17.97°C to 26.10°C, with April recording the highest temperature and January recording the lowest. The pH varied from 7.15 to 9.24, with March being the highest value and December being the lowest. The maximum and minimum values of transparency were recorded in the months of November and April, respectively, and ranged from 139.36 to 333.62 cm.

TDS value varies from 53.47 to 106.00 mg l-1 with November recording the lowest value and March posting the highest. Total alkalinity ranges from 59.33 to 71.33 mg l-1, and EC values vary from 107.20 to 206.00 µS cm-1. Both EC and total alkalinity were determined to be at their lowest and highest levels in the months of November and March respectively.

The total hardness value ranged from 63.93 to 82.00 mg l-1, with November obtaining the highest value and April documenting the lowest. The free CO2 value ranged from 0 to 4.26 mgl-1 and the highest was found in the months of November and December and absent in March and April. The maximum and minimum concen- trations of phosphate were obtained in February and January respectively and varied from 0.02 to 0.19 mg l-1.

The observed ammonia value range from 0.01 to 0.12 mg l-1 highest in January and lowest in Decem- ber. The nitrate concentration ranged from 0.04 to 0.14 mg l-1 with the highest in November and April and the lowest in December.

The highest nitrite concentration was recorded in April and the lowest in December with a range of 0.02 to 0.10 mg l-1. DO concentration was obtained highest in the month of November and lowest in January with a range of 5.93 to 11.47 mg l-1. The maximum BOD concentration was observed in the months of April and the minimum in November with a range of 0.20 to 2.60 mg l-1.

Among the water quality parameters measured ammonia, nitrate, nitrite, BOD and phosphate were observed to be higher in the cage area than in intermediate and control while DO was considerably low in the cage area than in intermediate and control but it was within the permissible limit.

A positive correlation was observed between pH and water temperature, water temperature and DO, DO and pH, hardness and EC, hardness and TDS, alkalinity and TDS, DO and transparency, and alkalinity and EC and EC and TDS. Whereas between TDS and transparency, EC and Transparency, free CO2 and BOD, free CO2 and hardness and free CO2 and pH showed a negative correlation.

Primary productivity (GPP, NPP and Chl-a) was also measured for both the sites (1 and 2) and showed variation in GPP, NPP and Chl-a in terms of months as well as distance wise. GPP was higher in the month of March and lowest in January and NPP was higher in the month of February and lowest in March.

Both GPP and NPP was higher at the cage area than the intermediate and control. Likewise, Chl-a was higher in the month of April and lowest in November and Control was higher than cage and intermediate. A total of 40 phytoplankton and 6 zooplankton genera have been identified during the study periods and Ceratiaceae was dominant in both sites (1 and 2).

CCA resulted that in the months of November, December and January, water quality parameters like nitrite, nitrate and free carbon had an influence on the population of plankton group Harpacti-coida, Gonatozy-gonaceae, Basi-llariaeae, Desmidia-ceae, Closteriaceae and Fragilariaceae. Whereas in February, phosphate, ammonia, and transparency were the effective factors for the variation in the population of Naviculaceae, Dinobryaceae and Zegne- mataceae.

pH, hardness, DO, EC and alkalinity were the factors that affect the distribution of Pleuro-sigmataceae, Catenu-laceae, Scenedes-mus, Branchioni-deae and Nostocaceae in the month of March and in April, water temperature and chlorophyll-a were the factors that influence the 98 variation of Asplan-chnidaea, Sphaerocystida- ceae, Cope-pod nauplii and Microcoleaceae.

In general, from the present study, we can conclude that few of the water qualityparameters assessed show a slight increase in the cage area compared to theadjacent area of the reservoir. However, the values ranged within the safe or permissible limits. Water quality parameters are an important factor that has to be considered solely for the purpose of management and sustainable utilization of a waterbody.

The quality of water varies between various water bodies as well as among various regions within a single water body. The long-term spatio-temporal dynamics ofvarious surface water body types and their potential driving forces over vast distances remain largely unknown.

Therefore, appropriate and in-depth biological investigations on the planktonic groups must be conducted in the future in order to understand the impact of water quality parameters on the dispersion of the planktonic groups. Since the cages installed in the studied area were on a small scale, the effect on the environment was not profoundly sound.

This could be due to the overall low input interventions in the cage functioning. The level of management in the studied cageswere semi-intensive types of management as the fish feed was used in subsistence amount as well as the stocking density of fish were below the optimum level.

Therefore, there is a scope for extension of cage culture practices to increase regional productivity as well as the standard of living for those living close to the reservoir's perimeter. Production can be increased by maintaining optimum stocking density with intensive management.

However, it is essential to regularly evaluate the water quality parameters so that the producer can modify management according to environmental factors, such as reducing fish density or altering feeding rates, to minimize or prevent deterioration of water quality so as to obtain sustainable utilization of the resource.


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