Pratap Mukhopadhyay
Aquaculture has a major role to play in contributing towards better human health and better ecosystem. The thrust needs to be on enhancing fish production in an environmentally sound manner. The emphasis has to be on good husbandry practices.
The role of aquaculture in providing nutrition and income to farming communities hardly needs any emphasis. To meet the ever growing demand for fish and fish products, the focus unfortunately has been on intensive rearing systems, resulting in over exploitation involving fish stocking densities much beyond the carrying capacity, frequent water exchange, inconsiderate application of feed, fertilizer and even scheduled chemo-therapeutic drugs like antibiotics. This has very often led to the generation of detrimental waste that has negative impact on the growth of aquatic life and biodiversity.
While bringing more area under rearing large fish, natural habitats of indigenous small fishes and prawns that contribute significantly towards rural household food basket, are being encroached. Also, while we claim to be the connoisseurs of fish and grow most of the fishes in the country, on the other side, the under-nourishment among school children is among the highest in the country. In rural Bengal, micronutrient deficiency is now a common sight among school children and womenfolk. Such nutritional deficiencies cause enormous national loss and need to be addressed before it is too late. Micronutrient deficiencies impair cognitive development and impair immunity as well as increase susceptibility towards infection. While fortification of food items of daily diet may be a recommended intervention strategy, but food based approach of increasing micronutrient status by increasing fish availability is a very simple and sustainable approach. In this context, the thrust need to be given towards enhanced fish production through inland freshwater aquaculture in an environmentally sound manner. The emphasis has to be on good husbandry practices.
Semi-intensive pond culture of Indian major carps (IMC) relies upon natural productivity (fish feeding on various planktonic food organisms naturally grown in the ambient water under the influence of sunlight) to a large extent. The major function of phytoplankton which include green, blue-green algae also called microalgae, is to supply dissolved oxygen during photosynthesis. Eventually they form food for zooplankton species, which again serve as most desired food source for younger fish species. The ability to support the growth of natural fish food organisms in the ecosystem is the result and effect of abiotic and biotic factors. Release of inorganic nutrients from pond soil in presence of sunlight enhances phytoplankton growth on which again the growth of zooplankton depends. Maintaining a balance of both these kinds of plankton population throughout the culture period, will therefore be of help in enhancing the survival and growth of fish like carps.
Environmental factors such as water temperature, light intensity, soil/water quality and their interactions determine the carrying capacity of a pond and thus influence the fish production. Also, there is ample scope for increasing the production by adopting better management practices and through supplementary feeding. Therefore, there is a strong need for optimum resource utilization to efficiently produce fish through adoption of simple management measures, relying on natural food in the ecosystem.
Adoption of better feeding methods
Semi-intensive farming of six cyprinid species (based mainly on the polyculture) is generally practised in freshwater aquaculture in India. Relying on natural food (zooplankton population) during early stages and delayed feeding with exogenous feed until later stages of growth, is a common practice among fish farmers. The young ones feed on the natural food – the mixed zooplankton including rotifers produced through pre-stocking pond manuring. ‘Critical standing crop’ (CSC), is a condition during which fish growth starts to decline from its maximum rate, soon after the food organisms decline. Beyond the CSC, the fish growth continues at an extremely slow pace because the supply of natural food becomes insufficient to meet fish requirements. This is the time when supply of acceptable quality of feed must begin to sustain its normal growth. A general survey indicated that farmers use nine major ingredients and five feed types. Ingredients are rice bran, groundnut oil cake, cotton seed meal, sunflower meal, soybean meal, mustard oil cake, sesame oil cake, wheat bran and maize meal. The feed types are rice bran only, rice bran and cotton seed meal, rice bran and groundnut oil cake; rice bran and sunflower meal and rice bran and mustard oil cake.
The form of the feed has an impact not only on the acceptance of the feed but also on the aquatic environment. Selecting proper time and fish size to start feed application should be a key factor in aquaculture. Providing feed when fish is below the CSC might lead to a waste of feed resources and an unnecessary increase in operational cost. Delaying the supply of feed will cause reduction in fish growth and yield. The frequency of feeding depends on body weight and water temperature. For instance, in case of larvae/spawn, the frequency of feeding may be several times an hour, while in case of juveniles, feeding twice a day may be considered sufficient. Optimal feed supply decreases competition for feed and hence size heterogeneity. Protein and energy concentration should remain balanced for maximum expression of the growth potential. Feeding practices should also be in tune with biological rhythm of the fish species, for example, catfishes generally show better feeding activity in the dark, while carp feeds in the day time. Understanding feeding behavior of aquaculture species is therefore necessary to establish an optimal feeding regime leading to homogeneity in growth and savings in feed costs.
Use of various substrata hiding in water can potentially contribute to the growth and production of different carp species through development of periphyton colonization on the substrata. Sugarcane bagasse, palm leaf, coconut leaves, bamboo poles in ponds provided with organic manure are some of the examples. The attached algae are stable leading to better accessibility to the grazing fish and also quantitatively more per unit water surface area. Increased availability of natural food organisms is also accompanied by positive impact on water quality.
Enhancing nutritional diversity
Small fishes can enormously contribute to micronutrient availability without having any adverse effects on the aquatic ecosystem and carp production. The small local freshwater species including minor carps, catfishes, murrels, perch, eels, feather backs and cichlids, for example, are self recruiting in nature and are able to provide enormous nutrition benefits. Fortunately, several non government development organizations and even Directorate of Fisheries have recently started polyculture of small local fish species and some kind of fish sanctuary has been proposed at several panchayats/villages. One such is located at Laxmikantapur in South 24 Parganas district.
Quality fish seed production
| Raising ducks on fish ponds promotes fish growth, fish yields, nutrient recycling, and enhances aeration in ponds. |
Farmers seldom take care of the parental nutrition component, which may result in low quality egg production, poor survival and slow growth. Since fish has high fecundity it hardly matters to the farmer or the field practitioner. A rohu for example, can have one lakh egg and even if more than 50% dies, the farmer will still have 50,000 spawn produced from a single fish.
Nutrition and feeding the broodstock remains the fundamental tool for successful reproduction, higher fertilization rate and resultant spawn viability. Provision of adequate nourishment supplying essential amino acid and fatty acid sources during pre-spawning phase (April to June) may ensure quality egg production.
Small scale Integrated Farming System
Integrated farming system is promoted with an objective to increase the productivity of water, land and associated resources while contributing to increased food fish production. Agriculture/ horticulture and aquaculture; duck, poultry and aquaculture; treated waste water –fed fish culture are certain examples.
Duck-fish farming is common throughout rural West Bengal. Duck-cum-fish culture involving low stocking density relies primarily on natural food produced in water as source of nutrients. Generally, the variety of duck – ‘Indian Runners’ is preferred. Presence of ducks help in eradicating many insect pests, tadpoles and help in creating a conducive ambience for fish to thrive and grow. Nitrogen rich duck droppings enhance production of natural food organisms. Duck droppings go directly into the pond, providing Carbon, Nitrogen and Phosphorus, stimulating the growth of natural food organisms. For these simple reasons, raising ducks on fish ponds promotes fish growth, increase fish yields and eliminates pollution problems. The stocking rate of ducks is generally 300-500 ducks/ha and each duck produces about 7 kg of dropping during the 36 day fattening period. If 500 ducks are raised, 3500 kg of excreta would be produced in this period. Ducks help in releasing nutrients from pond bottom also. Fish-duck integration also promotes the recycling of nutrients in the pond ecosystem. In shallow areas, a duck dips its head to the pond bottom and turns the silt to search for its food. By virtue of this digging action, nutritional elements locked in the pond humus get released. Ducks also act as pond aerators. Their swimming, playing and chasing disturbs the surface of the pond and aerates the water.
Rice-fish farming system is generally found in the districts of Malda, east Midnapore, Hooghly and South 24 Parganas in West Bengal, during kharif season every year. Prior to initiating fish culture, land preparation /land shaping is essentially undertaken. Initially, peripheral trenches with 1 m wide x 1m deep and 25 cms high are dug by placing bamboo pipes and screens at inlet and outlet. These trenches serve as refuge for the fish and pass way for their easy movement around the paddy field. In such rice field areas, the water depth is favourable for fish in comparison to other rice ecosystem. There are several benefits owing to rice fish culture. It is reported that rice yields increase when integrated with fish than without integration. There is a reduction in rodent infestations in the rice field because of continuous submergence; the submerged part of the rice plant serves as essential food for fish.
End note
Aquaculture and its management in general has a major role to play in contributing towards better human health. It is important therefore that available water bodies under all panchayats/talukas be utilized for aquaculture. The vast array of agro based by-products available in rural India for potential application in fish culture practices need to be tapped to attain the maximum genetic potential. This can truly make major carp culture remunerative and help improve the livelihood support of rural population. Social aquaculture in the line of social forestry be introduced wherever possible utilizing the small indigenous fish species. This may serve the dual purpose of conservation of these species some of which are becoming endangered as well as production of cheap and best edible animal product for better human health.
Pratap Mukhopadhyay
Retired Principal Scientist
ICAR-CIFA (www.cifa.in )
E mail: pratap_in2001@yahoo.co.uk
