Effects of cage culture in... Physicochemical parameters and primary productivity of Loktak Lake

Elezabeth Haobam / MK Datta / Y Bedajit / Ch Basudha / P Bhattacharjee *

Cage culture is the practice of raising fish in captivity in an enclosed area that maintains the open exchange of water with the surrounding water body, from fry to fingerling, fingerling to table size or marketable size. They can be used in variety of water resources, including lakes, reservoirs, ponds, and rivers because of their simple installation, use of existing water bodies, and flexible management.

Researchers and commercial farmers are paying more attention to the aqua-culture technique known as cage culture in order to boost productivity, fulfill the population's growing need for fish, provide more affordable sources of protein, and the need to create jobs in the fishing industry.

With the benefit of a cost-effective construction that can be used in any form, size, or water body, it is also simple to harvest and requires minimal manpower. Farmers and the State Fishery Department have embraced cage culture in an effort to increase fish production in Manipur and make the State self-sufficient.

In the context of sustainable use of fishery resources and the water body, the present study was conducted by Elezabeth Haobam, Post Graduate Scholar under the Department of Fisheries Resource Management, College of Fisheries, Lembucherra, Tripura, Central Agricultural University, Imphalto evaluate the effect of cage culture on the physicochemical parameters and to know the primary productivity of the sampling site. If cage culture has any adverse effects or has no effects.

Fifteen water quality parameters such as electrical conductivity, total dissolved solids, pH, water temperature, total alkalinity, total hardness, free CO2, dissolved oxygen, biological oxygen demand, phosphorus, ammonia, nitrate, nitrite, and chlorophyll a. for soil pH and organic carbon of soil, were conducted.

According to our current research, the water at the sampling station has a slightly acidic to alkaline nature pH, low soil pH, and a high organic content because of the presence of Phumdis. It also has the typical characteristics of soft water and low nutrient content during the sampling period. The soil pH is also acidic in nature with high organic carbon content.

In all the seasons, the post-monsoon period has the highest concentration of nutrients like nitrite, nitrate, ammonia, and phosphate. As a result of the monsoon period's precipitation, which causes nutrient leaching and draining into the water body, the nutrient concentration was likely to rise. The majority of water quality indicators were within acceptable limits and had no negative effects on the water's quality.

Two water parameters, in particular, ammonia and phosphate, were excessive at the sample stations attributable to anthropogenic activities other than cage farming. But there was no discernible variation between the sampling locations, indicating that the increase in ammonia concentration is related to factors other than feeding and the discharge of feces.

The lake's BOD was determined to be above the allowable limit, indicating water pollution, though not at an alarmingly high level. Washing, bathing, and disposing of animal waste are done in the lake by the residents.

Gross Primary Productivity and Net Primary Productivity were observed to be high in winter and pre-monsoon and it was observed within an optimum range throughout our study period and the chlorophyll-a concentration of the sampling sites was in the optimum range below 100 µg/l, and was high during the winter season.

From the sampling stations we observed 46 phyto- plankton, 7 zooplankton, and 4 protozoa taxa belonging to seven classes
(i) Cyanophyta,
(ii) Chloro- phyceae,
(iii) Trebou-xiophyceae,
(iv) Bacillario- phyceae,
(v) Conjugato-phycea,
(vi) Dinophyceae, and
(vii) Chrysophyceae.

A high level of diversity was observed in plankton with more species diversity in winter and pre-monsoon. Phytoplankton was more prevalent as compared to zooplankton. There were no distinct indicator species observed at the sampling sites as most of the plankton found were recorded by previous studies in Loktak.

The canonical correspondence analysis with seven- teen abiotic factors explained 25.62% and 25.47% cumulative variance of planktons along the two axes. With phosphate and depth, DO have a major impact on the dispersion of phytoplankton communities during our study course.

During our investigation, we noticed that fish didn't grow to their full potential, that some sparse feeding occurred at specific times of the day, and that the net was clogged with periphyton. Due to rainfall, temperature changes, and water precipitation, there was a seasonal variation in the water quality indicators.

Other than nitrite, there are no other water quality parameters that significantly vary with time or distance. And the bottom of the cage always touches the soil bed because Loktak's depth typically does not go beyond 6 meters. The six-month experi- ment was carried out at two cage culture locations in Loktak Lake, Manipur.

We found that all of the cages were not being used for fish culture, and the species that were cultured including Ctenophyragodonidella, Labeo bata, Osteobrama-belangeri, and Labeorohita were put in a few cages.

Low feeding rates were used and feeding was done sporadically and they performed a three-month culture cycle. From the present study, we conclude that cage culture in Loktak Lake can be increased in a properly managed way as there is no adverse effect from the current capacity of cage culture.