Small water bodies in rainfed and irrigated areas, mostly comprising ponds, tanks including flooded rice fields, wetlands and reservoirs constitute a huge freshwater aquatic resource system which represents immensely high natural productivity and fisheries production potential.
In terms of captured and cultured fish and other aquatic products the small water bodies contribute very significantly. Due to highly complex and diverse environment and small scale operation of individual units a precise estimate of their fish production, fishery and aquaculture potential is hard to assess. The growth of aquaculture over past several decades has, however been phenomenal in harnessing this resource base.
Even so, there is a far too wider gap between area under aquaculture and the vast available resources either still under capture fisheries or remaining unutilised. The foremost requirement to tap the large opportunities for improved fish production in freshwater, therefore is to bring about a horizontal expansion in resource-use by employing scientific technologies.
The increase in fish production in small water bodies could be realised basically by a balanced approach of optimising the utilisation of the whole ecosystem, manipulation of stock and species, manoeuvring habitats favourable to target fish species, enriching nutrients level for growth of fish food organisms and necessary health care for growth and survival. All of these are the very basis of enhancement interventions converging on combined attributes of aquaculture for increasing production.
Most of the enhancement technologies are framed with detailed considerations on physical (morphometric, edaphic and hydrologic) and biological (food web, life history, species interaction, carrying capacity) factors to achieve closer to the natural limit to production potential.
Capture Fishery and Culture based Capture Fishery:
The capture fish production is largely dependent on the size of the water body and natural resource management, with either effort control or mesh-size regulation as the best method of sustainable fishery exploitation.
In capture fishery the lowest trophic level of harvestable community holds out the largest natural potential, and therefore, multi-species fishery and multi-gear fishing pattern are highly promising to improve productivity.
In relatively larger sized water bodies culture based fishery enhancement yields good results by relying on a realistic stocking protocol and species composition, usually with carps. A limited level of fertilisation also helps to raise the productivity of natural environment. Culture based capture fishery production is a function of stocking density of a combination of species, which serve as strong fundamentals of stock enhancement.
Selection of species and appropriate balance in mixture of species for stocking are decided keeping in view the physical parameters, optimal exploitation of the available trophic levels and spatial niches. Stocking of large sized fish fingerlings is an effective way to reduce predation and increased in yield from the system.
For long term and sustainable increase in production, however, there is also a need to increase the carrying capacity of the system which is easily brought about by nutrient enhancement through variable levels of external fertilisation.
Raising the carrying capacity is feasible and relatively better manoeuvrable in small water bodies. Since the water bodies in rainfed regions are found in coastal plains or river basins the changes in hydrological regimes are intimate related to productivity, mediated by greater access to nutrient inputs through run-off or inundation by floods in a natural manner.
Production enhancement measures in small water bodies yield greater dividends as one moves from capture fisheries to culture based capture fishery but the highest return is invariably expected from the scale of operation using aquaculture technologies.
Operational Level of Culture and Options
The purview of size of small water bodies is generally considered to be up to 20 or 25 ha in area, in various state of use or non–use for several reasons. Those that are in some form of use are usually under aquaculture production for finfish. These water bodies have a substantial potential for fishery enhancement using a range of standard technologies. These technologies tend to harness the efficiency of interaction between energy and nutrients, particularly the dynamics of variability of area, volume, water depth, light, temperature and addition and recycling of primary nutrients.
The magnitude of production per unit area varies with the level of interaction and control inbuilt in the technological intervention. The culture system adopted could vary with size of operational unit. Usually large water sheets could be exploited well by extensive aquaculture where only stocked fish species is harvested utilising natural ecosystem productivity.
Semi-intensive culture system may yield good production in medium sized water bodies where high density of stocked fish grow better, aided by fertilisation and supplementary feeding as a further boost to natural productivity. In intensive culture practices adopted in small water bodies (1-5 ha), a greater thrust on supplementary feeding is given in addition to fertilisation to sustain intensive stocking level. Super intensive system of culture serves to sustain very heavy density of stocked fish by resorting to intensive management measures including balanced diet, aeration, water exchange, health care and vigilant monitoring.
Fish Seed Resource – An Important Pre-requisite
If culture techniques are to be employed to the vast resource of small water bodies for increased fish production, the basic requirement is to meet the enormous demand of fish seeds as stocking material. This alone could ensure a rapid transition and transformation of small water bodies into most valued fish production units.
The first measure in this direction is to create fish seed infrastructure consisting of hatchery, nursery and rearing facilities widely spread over vantage locations in different parts of the target area. A farm based approach which integrates all the three components of seed production along with the grow-out culture facilities is an ideal proposition. Alternatively hatchery, nursery and rearing units could be developed separately at convenient locations. Well developed and tested technologies are readily available to implement this strategy.
Incidentally, production of spawn, fry and fingerlings is known to yield dividends several times over in comparison to table size fish production on unit area basis. The other advantage is that the smallest and seasonal water bodies (0.05 – 0.2 ha), which may be retaining water for only two to four months are best used as nursery and rearing units. In terms of area, one hectare each of nursery and rearing facility is likely to cater to more than 200 hectares of culture area.
On a modest estimation, the nursery stocked @ 3 – 5 million spawn per ha produces 1 – 2 million fry at 50% survival in one cycle of 15 days. In a season of 3 – 4 months the fry production from one hectare nursery may touch ~9 million fry (20 mm). The rearing ponds stocked @ 0.3-0.4 million fry per hectare would yield ~0.2 million fingerlings (100 mm size) in three months allowing for 20% mortality. The stocking requirement for grow-out culture units amounts to a maximum 0.001 million fingerlings per hectare.
The hatchery produced spawn of target species, especially carps could be utilised to raise fingerlings as stocking material. Fish breeding by hypophysation, multiple carp breeding and the hatchery technology have brought about spectacular advantage to practising farmers interested in seed production who may have great contribution in horizontal spread of aquaculture to increase fish production in small water bodies.
Polyculture of Carps
Polyculture of carps is widely recognised as the most popular and suitable option to enhance fish production from small water bodies for several reasons. It offers a wide choice of farmer-friendly culture systems with production potential ranging from 2- 15ton of fish per hectare per year, depending on different level of technological application, scale of input use, investment structure, infrastructure size, hydrological regime and geophysical and location specificity.
Carp polyculture is a versatile form of culture system that easily integrates with agriculture, horticulture and livestock based system with high degree of complementarily in terms of resource-use and production benefits. Considering that only a meagre 40 % of available aquatic resources in the form of small water bodies are now under some form of farming practice, a horizontal spread of polyculture on an extensive or semi-intensive scale is sure means of manifold increase in fish production.
Basically polyculture of Indian major carps or together with exotic carps (composite carp culture) could be taken up in fertiliser and feed based farming system integrated with agriculture / livestock farming. At suitable areas of larger weed infested water bodies cage culture and pen culture would provide alternative means of enhancing fish production.
The spread and growth of carp culture so far has not been consistent and therefore, the priority measure appears to be adoption of scientific package of practices for optimising fish production.
Generally, rectangular ponds of 0.5 -2 ha which retain at least 1.5 m water even in dry season perform best as productive units, while smaller and shallow ponds affect growth of fish. For ensuring survival, growth and high yield of fish the ponds must be freed from weeds, predators, following standard pond preparation methods. A further requirement is to manage desired water quality and nutrient concentration for enriched natural food organisms.
Preventive weed control measures like deepening pond margins, desilting, ploughing of marginal weed prone areas and providing barriers against entry of weeds are essential part of management. The inherent productive capacity of the pond and the status of plankton density is often required enhancement through manuring and fertiliser application in direct relation to targeted stocking density of fingerling. For a medium productive pond raw cattle dung @15 t, urea @ 200 kg and single super phosphate @ 300 kg per hectare per year applied at convenient split doses suffices for good production. Higher doses of organic manure may be required in newly dug out or sandy bottom ponds.
High yield of fish are invariably linked to the size and density of stocked seed, but it offers a good deal of flexibility as well. Fingerling of 50 -100g size stocked at a density of 8000- 10000 per hectare often produces 8 -10 t fish per ha per year. Adjustment of species ratio is a crucial decision for optimising production, which needs to be worked out to minimise interspecific competition for food available at various trophic levels or different euphotic zones of the culture environment.
A combination of six species of 3 Indian major carps and 3 exotic carps viz., grass carp, silver carp and common carp, comprising surface, column and bottom feeder species ideally meets the requirement of highest production in ponds with sufficient depth.
The standard approach is to maintain the proportion of 35% , 30% and 35% as surface, column and bottom feeders in stocking, which is subject to readjustment after assessment of growth performance, contribution of individual species by weight at harvest, availability of stocking material, variability in physical conditions (water depth) etc.
Variability of water depth, surface richness in plankton, organic sediment of bottom, dissolved oxygen level and their manoeuvrability are some of the other criteria that provide a good lead to manage species combination (3, 4 , 5 species) and their stocking ratio.
The scope remains wide open to introduce other fishes as culture component for utilising the unutilised niches in the ecosystem for production enhancement. To take advantage of temperature regime on fish growth, stocking is preferably done in June –July in culture operation of 10 12 months before harvest. Limitations imposed by natural fish food production capacity of the pond to sustain heavy stocking density, supplementary feeding becomes essential.
Formulated feeds prepared with balanced composition of protein, carbohydrate, fat, minerals and vitamins are ideal feed material. Alternatively, a mixture of groundnut oil cake (40%), rice polish (40%), soyabean meal (15%), fish meal (4%) and vitamin-minerals (1%) could be fed at the rate of 1 – 2% body weight of standing stock on a daily basis to grow the fish.
Deficiency of dissolved oxygen sometimes poses a practical problem in growth of fish, especially under heavy stocking and feeding regime. Various methods of manual /mechanical aeration are good aids to combat the situation, particularly during prolonged cloudy weather conditions. Water exchange or water replenishment at periodic intervals to maintain appropriate water level also serves to boost fish growth and production in semi-intensive and intensive culture systems.
Potential of Native Catfish Culture
After carp polyculture, an advantageous, non-competing second line of fish production enhancement in small water bodies comes in the form of native catfish culture. Catfish culture is easily adaptable in water bodies categorised as fallow, swampy, marshy, weed-choked and derelict environments that are patently unsuitable for carp culture practices.
The rainfed regions abound in unutilised sprawling water impoundments with poor environmental conditions characterised by heavy organic load, anoxic water mass. With simple management, it is feasible to turn them into production base for propagation and culture of a number of native air breathing fishes of commercial importance, like Clarias batrachus, Heteropneustes fossilis, Chitala chitala, Notopterus notopterus, Mystus spp., Channa spp Anabas testudineus etc. These fishes breed naturally and complete their life cycle in ponds, swamps, paddy fields and low lying inundated impoundments and are capable of surviving in shallow stressed environments.
The fishes respond well to simple culture protocol of low risk, low input and low investment, under usually adopted heavy stocking and short duration multiple cropping. Despite the potentiality of many catfishes, Clarias batrachus and Heteopneuste fossilis have gained wide popularity for pond farming, both in monoculture and poly culture systems, which yield 3 -5 t/ha in 6-8 months at stocking density of 0.02 – 0.05 m fingerlings per hectare.
Stocking and feeding are the only measures required in their management. The breeding and seed production technique is available and is easy to handle. Catfishes are easily bred by injecting synthetic hormone Ovaprim or Ovatide intramuscularly at a dose of 0.4 mg per kg body weight. Collection of fry from natural waters like irrigation canals and paddy fields, where they are found in nests on the margin at about 0.5 m below water surface, may also meet farmers’ requirement to a large extent. Considering high market demand and consumer preference, the pond culture of other air-breathing catfishes under controlled conditions has to standardised and propagated in a big way.
Given some extra effort in pond management it is also feasible to develop and popularise captive culture of a number of highly preferred non-air breathing fish like Pangasius pangasius, Wallago attu, Sperata seenghala, Mystus aor, Ompok pabda, Ompok pabo, Ailia coila etc. These measures will contribute towards enhancing fish production by utilising available aquatic resources.
Harnessing the Potential of Small Indigenous Fishes
The small indigenous fishes (growing up to 30cm in length) in rainfed areas constitute a vast resource in terms of species richness and their role and contribution towards food and nutrition of rural masses. They are found extensively in a variety of natural habitats like ponds, tanks, streams, wetlands, rivers and even pools, ditches and derelict water impoundments.
Right from overexploitation of fishes arising from growing demand for fish everywhere, to many other serious repercussions from habitat degradation, pollution, siltation, water abstraction, invasion of exotic species and irreversible artificial hydrologic changes imposed by dams and barrages etc., have combined to pose a huge threat to the biodiversity of small indigenous fishes and their ecological support system.
The most effective turn around and reversal of this adverse situation is possible through the role of aquaculture enhancement in small water bodies and captive breeding technology development for selected small indigenous fish species of high importance. Some of the leads and successes in small scale aquaculture of Amblypharyngodon mola, Puntius sophore, Osteobrma cotio, Cirrhinus reba, Labeo bata, Gudusia chapra alongwith Indian major carps already established as a technology are necessary to be replicated widely in extensive areas.
Greater thrust is required to include potential species for aquaculture diversification, the prominent among which are Labeo gonius, Labeo boggut, Labeo dussumeri, Labeo fimbriatus, Puntius pulchellus, Puntius kolus, Puntius sarana, Cirrhinus cirrhosa etc. Farmers in some areas are already culturing these species with seed collected from the wild. Similarly the success in captive breeding of several small indigenous fishes reported by different scientific bodies needs to be further enlarged in scope to include more of the dominating groups of fishes in different locations and habitats with intensive efforts on rapid dissemination of technologies to grass root level. The attempts to produce more fish from small water bodies will get a boost from such measures.
Freshwater Prawn Farming
The culture of giant freshwater prawn, Machrobrachium rosengergii and Indian river prawn Machrobrachium malcolmsonii is a versatile proposition to enhance production form small water bodies. The success achieved in prawn hatchery and commercial prawn seed production by hatchery owners has virtually removed all hurdles in implementing prawn farming in all geographic locations.
For nearly past 10 years freshwater prawn farming has seen unparallel growth and achieved a production level of 1 – 1.5 t per hectare in 7 -8 months in monoculture operations. Poly culture of freshwater prawn in composite fish culture ponds has also been very successful. With these indicators, freshwater prawn farming is to be viewed a lucrative measure for aquatic resource utilisation, particularly for small water bodies in rainfed areas.
When the small water bodies are elevated from lower to optimal level of utilisation incorporating any of the several technology-based fish production systems, it is time to go for a measure of integration of fish with agriculture / horticulture, poultry, duckery, livestock production system. The underlying idea is to combine fish with two or more farming systems to obtain higher productivity per unit area and to maximise utilisation of waste / by-product from one system in another.
Since fish farming is virtually organic based system depending mainly on animal wastes as fertilisers or agricultural by-products as feed, integrated aquaculture is a sound economic proposition. An overall production of up to 5 t of fish per hectare per year is easily obtained in an integrated system with poultry / duckery / piggery /cattle with very little to invest on feeding the fish. The embankment or adjacent land of small water bodies may provide facility for the chosen component of the integrated system without involving too much investment.
Community Based Farming and Extension Support
The major key factor in transforming small water bodies into a production base and elevating fishery productivity is to involve grass root community participation. The role of technology will come into full play and produce result when it is appropriately transferred to the end-users.
Strong extension support for hands-on training and demonstration sufficiently of large scale in its spread and intensity is considered a priority measure and a standard pre-requisite. The location specific differences and variability in geomorphometric and agro-climatic conditions in the performance and/or choice of technology are likely to create major hurdles to the desired outcome. These are resolved practically through a planned process of location specific technology refinement by on-farm testing and front-line demonstration.
Empowering the rural masses with technology and skill to enhance fish production in small water holdings comprising a large target area will produce enormous scope of employment generation and economic upliftment of the rural scenario.
Dr. Bana Behari Satpathy