Associate Professor

Department of Zoology

SBP Government College

 Dungarpur, Rajasthan, India 

Associate Professor

Department of Geography

SBP Government College

Dungarpur, Rajasthan, India

Reservoirs are defined as man-made impoundments created by constructing dams or other barricades across rivers or streams (Sugunan, 1995). Although reservoirs offer immense scope for achieving high fish production yet their potentiality is not being harnessed properly. Generally reservoirs are meant for hydel power generation, irrigation, supply of drinking water, etc., So, the existing ecological conditions can not be altered because sharp fluctuation in the water level brought about by the constant inflow and outflow of the water. However, their natural biogenic production potentiality can be profitably exploited for enhancing the fish yield through the adoption of scientific management techniques of stocking and harvesting. Due to the inadequate understanding of their production dynamics and consequent low level of adoption of the scientific management strategies, a vast majority of them remain either undeveloped or underdeveloped.

Hence, the Reservoir Division of the Central Inland Capture Fisheries Research Institute undertook detailed investigations to evaluate the production potentiality of some of the small reservoirs. The studies have brought to light the reasons for the low fish yield being obtained as against the great production potentiality in these small reservoirs in Peninsular India. The ecology based investigations had helped to formulate certain valuable guidelines that would go a long way in bridging the wide gap between the great production potentiality and the actual yield being obtained from these reservoirs.

I. Importance of ecological investigations:

For fishery development in the reservoirs, the detailed investigations on various ecological parameters are the prime requirements. The formation of the reservoirs across the rivers bring about very conspicuous changes in the ecological conditions which is influenced by the morphological, edaphic and climatological features. Since the production potentiality of the reservoir is determined by the inherent quality of water and soil, inflow of nutrients, the quantity of the constant inflow and outflow of water, etc. Hence, it is paramount importance to have a thorough understanding of all the ecological conditions including the physico-chemical parameters of water and soil, the biotic communities like plankton, periphyton, benthos, primary productivity, etc. before planning the course of actions for enhancing the fish yield from the reservoirs (Selvaraj et al., 1997).

II. Importance of stocking:

1. Existing fish fauna : To assess the existing fish fauna in the reservoir, detailed investigations have to be undertaken. These investigations would help to find out not only the existence of the unwanted as well as the commercially important species of fishes but also the extent of their contribution to the yield of the reservoir could be assessed. After making such investigations, it could be decided about the introduction of the fast growing carps for enhancing the fish yield. It is also important to investigate the maturation and breeding behaviour of the different fast growing carps which are introduced into the reservoir. There were instances where the carps introduced failed to attain proper maturation in their establishing in the reservoir (Joseph et al., 1990 ; Selvaraj et al., 1997). Hence the fishery has to be sustained through regular stocking of advanced fingerlings of the fast growing major carps.

2. Size of the fingerlings to be stocked:  the size of the fingerlings is an important factor while stocking. Generally to achieve the target of seed production in the farm as well as achieving the target of stocking in the reservoir, the early fry are stocked in the reservoir. This results in heavy mortality during the transport and also in the reservoir due to predation by piscivorous fishes already existing in the ecosystem. Moreover, it is desirable to rear the fry in the farm ponds till they attain the size of advanced fingerlings of more than 100 mm in length which would ensure better survival of the seed stock in the reservoir.

3. Density of stocking: The reservoirs should be in relevance to the carrying capacity the reservoir. High stocking density may results in heavy mortality and poor fish yield. The studies have indicated that the stocking density can be drastically reduced when the reservoirs are stocked with advanced fingerlings of over 100 mm in length. It is found that it is sufficient to stock the small reservoirs at a low stocking density of 200-300 advanced fingerlings of major carps. (Selvaraj, 1998)

4. Ratio of different species stocked: There are various biotic organisms available in the reservoir ecosystem with the different feeding niches. With the background knowledge of the food and feeding habits of different species of fish it becomes easy to decide about the ratio of the species to be stocked. The ratio of the different species also depends on their different growth rate in a particular ecosystem with different feeding niches. Hence, it is highly essential to assess the growth rate of different species. This can be carried out through various marking techniques. The method of group marking through clipping of the pelvic fin has been proved to be more successful means to evaluate the growth rate of different fishes in the open water ecosystem (Selvaraj et al., 1987, Murugesan et al., 1990). The manual removal of the pelvic fin from advanced fingerlings of carps with fingers has proved to be very effective means of marking the carps. The process is easy to perform and saves a lot of time in marking a large quantity of fingerlings at a time. The wound caused by clipping of the fin is treated with hydrogen peroxide, followed by an application of furacin cream to avoid any possible infection. The rate of recovery of the clipped specimen was ranging from 5.8 % (rohu) to 43.2 % (catla). Thus the method of clipping for group marking helps not only for assessing the growth rate and survival of different species of fishes but also for formulating the stocking and exploitation strategies so as to achieve a sustained optimum yield from the reservoirs (Murugesan, et al., 1998).

1. Period of stocking: The reservoirs are often stocked within a short period between August and October every year, resulting in heavy competition for food among the seed of the same age group and also there is a great stress on the population density at a given time of the year. This results in stunted growth and subsequent heavy mortality, leading to poor fish yield. The studies have indicated the need for stocking the seed through all the months of the year to ensure better survival and growth of the stocked varieties of fishes (Selvaraj and Murugesan, 1990).

Ill. Importance of judicious harvesting:

It is advisable to operate gill-nets with 50 mm meshbar so as to ensure the harvesting of fishes of more than 1 kg in size. As it is well known, the financial return through the sale of major carps of more than 1 kg in size is much more than the sale of undersized fishes due to the difference in the selling price. Besides, the fishes must be provided with enough opportunity to attain the harvestable size within the shortest time possible because of their great growth potentiality during the early part of their free-life period in the reservoir.

IV. Conclusion:

The adoption of the scientific management techniques resulted in increased fish yields. Simultaneously, it was also recorded that the medium and minor carps and also other miscellaneous uneconomic species of fish have almost disappeared (Selvaraj and Murugesan, 1997). Besides,  it was also recorded that catch per unit effort increased conspicuously as against the poor catch per unit effort obtained before the adoption of the scientific management techniques. As a result of the better management strategy, the revenue also increased substantially.

The investigations have revealed that the fish yield depends more on the quality of the seed stocked rather than their quantity. The studies have established that the small reservoirs can contribute substantially to the freshwater fish production. Even at a modest yield, a significant improvement in the revenue can be achieved through the adoption of the scientific management techniques. Thus the results obtained in various reservoirs have established that there is tremendous scope for achieving several-fold increase in fish production from all such reservoirs, irrespective of the area of the reservoir or the existing fisheries in the reservoir through the adaption on these techniques to suit to the local needs of any such reservoir in the region.

References:

1. Joseph, K.O, C. Selvaraj, V.K. Murugesan and P.K. Aravindakshan, 1990. Observations on the effect of low electrolyte reservoir water on carp 'eggs hatching and survival rate. In: (Eds.) Jhingran, Arun, G., V.K. Unnithan and Amitabha Ghosh. Contribution to the fisheries of inland open water systems in India, Part I, 141-146.

2. Selvaraj, c., V.K. Murugesan and V.K. Unnithan, 1997. Ecology-based fishery management in Aliyar reservoir. CIFRI Bulletin No. 72

3. Selvaraj, C., Mathew Abraham and K. Gopinathan, 1987. Validity of fin-clipping to 'study the

growth rate of Gangetic carps in Aliyar reservoir, Tamil Nadu. Inland Fish. Soc. India, 19 (1): 74-77.

4. Selvaraj, C, 1998. Management of Inland Open Water Fisheries. CIFRI Bulletin No. 83

5. Sugunan, V. V. (1995). Reservoir Fisheries of India. Food and Agriculture Organisation of the United Nations