Abhed Pandey and Sachin Onkar Khairnar
Most forms of traditional aquaculture rely largely on the production of foods through natural processes, or by fertilization and water management in enclosed areas. But for enhancing production, supplementary feeding is opted to ensure the adequate availability of food in high density carp culture.
Aquaculture is the farming of aquatic organisms in both coastal and inland areas involving interventions in the rearing process to enhance production. It is probably the fastest growing food-producing sector and now accounts for 50 % of the world’s fish that is used for food. Recent development in the aquaculture sector and the increasing demand for fish production has resulted in intensification of the aquaculture practices.
In India, carps are dominant in freshwater aquaculture, and they contribute more than 85 % of the total production. The Indian major carps (IMC), namely catla (Catla catla), rohu (Labeo rohita) and mrigal (Cirrhinus mrigala) dominate aquaculture production. Although, Chinese carps such as common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella) and silver carp (Hypothalmichthys molitrix) are also cultured, their popularity in the market remains low. Their ability to filter feed by harvesting the natural plankton produced in the system through fertilization, provide the opportunity for low-cost aquaculture systems with reduced risk to farmers.
Significance of natural feed and supplementary feeding
With the increased commercialization of carp farming and greater market focus, demonstration of the new balanced commercial diets that promote optimal fish growth and health is undertaken by feed industries. However, the majority of farmers in most parts of the country continue to depend on a conventional mixture of rice bran and oil cake as the common supplementary feed. Fish requires adequate nutrition in order to grow and survive. Nature offers a great diversity of food to fish, including plants and animals. The plankton is an important component of aquatic eco-system, as it contributes significantly to primary production and represents readily available food for fishes. Though ponds are fertilized by organic manures and inorganic fertilizers for the proliferation of natural food organisms (plankton), supplementary feed must be used to meet the nutritional requirement of carps.
Carps are either herbivorous or omnivorous in nature and can be easily reared using supplementary feed. The importance of supplementary feeding varies according to the required intensity of cultivation. For proper growth of the fish, supplementary feed must contain protein, carbohydrate, lipid, vitamin and mineral in sufficient amount. The knowledge on the specific requirements of carps is essential for the successful semi-intensive and intensive fish culture where it is required to maintain a high density of fish than the natural fertility of the water can support.
The quantity and quality of feed consumed have a pronounced effect on growth rate, feed conversion efficiency and body composition of fish. Applying supplementary feeds in a fish pond can significantly raise the yield. The feed is directly consumed by the carps and, in turn, their excreta act as the manure in the pond water. This multiplies the natural food organisms of the plankton feeders.
The supplementary carp feed should have following characteristics:
Characteristics of supplementary feed
- Water stability
- Easily available and cheap
- Easily acceptable
- Easily digestible
- Causing less pollution
Nutrient requirements in carp
In carp farming, nutrition of fish is critical because feed represents 50-60% of the production costs. Protein is very important. The carp feed contains 25-35% crude protein, 28-38% carbohydrate, 6-8% crude fat and crude fibre, 2% vitamin-mineral mixture and 0.5% common salt. Crude fat and crude fiber requirement of carp feed ranges from 6-8%. (Table 1).
Table 1. Nutrient requirement (%), gross energy (cal/kg) and poly unsaturated fatty acids (PUFA, %) for different life stages of carps
|S. N.||Characteristic||Larval feed||Fry feed||Grow-out feed||Brood feed|
|Acid insoluble ash||2.5||3||3||3|
*Source: 8Paul et al (2017).
Major ingredients in carp feed
The major ingredients in carp feed consists of rice bran, groundnut oil cake, sunflower meal, soybean meal, mustard oil cake, wheat bran, common salt and mineral mixture. The feed types used are rice bran alone, rice bran and groundnut oil cake, rice bran and sunflower meal, and rice bran and mustard oil cake. Moreover, some farmers also prepare feed mixtures using a variety of locally available resources, including fishmeal (Fig. 1a).
The feeding strategies play an important role in maximizing nutrient availability and can determine the success of a culture operation 2. Specifically defined feeding strategies have been adopted to minimize feed wastage and nutrient loss by leaching and to maximize growth. The unconventional feeding strategies such as stop feeding, break feeding, bag feeding, feeding enclosures, gelatinization etc. are practiced in the country. In India, innovative thinking and experimental ability of its fish farmers, who have developed their own successful feeding strategies, have contributed towards boosting carp fish production.
Generally, in carp farming two types of feed are used; farm-made or commercial manufactured. Feed formulation can be done by using various locally available conventional and non-conventional feed resources. The feed formulation for carp species at different life stages is tabulated in Table 2.
Table 2. Important feed formulations for various carp species*
|Spawn||1||Finely powered soybean meal Finely powdered groundnut oilcake Finely powdered fish meal Finely powdered rice-bran Vitamin and mineral premix Phospholipid (as soya lecithin) Veg. Oil : fish oil (1:1)||10.0 32.0 20.0 30.0 2.0 4.0 2.0|
|Fry||2||Groundnut oilcake Soybean meal Rice-bran Meat meal Vitamin mineral mix||28.0 20.0 30.0 20.0 2.0|
|Fingerlings||1||Soybean meal Groundnut oilcake Mustard oilcake Rice-bran Vitamin-mineral premix||7.0 30.0 35.0 26.0 2.0|
|2||Groundnut oilcake Soybean meal Fish meal Rice-bran Vitamin-mineral premix Vegetable oil||40.0 20.0 8.0 30.0 1.5 0.5|
*Source: 8Paul et al (2017).
Different forms of carp feed
1. Powdered feed (Mash)
In this method, the feed ingredients are mixed (Fig. 1b) as per the required composition of the feed after proper grinding of the ingredients. Fine ground/powdered feed (Fig.1c) is used to fed carp spawn and fry. Whereas, fingerlings and adults/brooders are fed with feed balls/dough (Fig.1d) made from soaked feed.
2. Componded pelleted feed
Farm made pelleted feeds can be prepared by using hand pelletizer (Fig. 1e) and/or motorised pelletizer (Fig. 1f). Moisture content in the dried feed varies between 7-13%, so it can be stored for longer period of time and transported from one place to another. The pelleted feed is given to carp fingerlings and onwards stages. Further these pelletes are classified into two type:
- Sinking pellets: Sinking pellets (Fig. 1g) are dense, heavier and sink in the water immediately after broadcasting.
- Floating pellets: These pellets contains less moisture, are light in weight and have air- pockets due to which feed floats on the water surface, which helps to know the amount of feed consumed by the fish.
Advantages of floating pellets
- Easy to ingest
- Easy to digest and absorb
- Reduce leaching of vitamins and other nutrients
- Less feed wastage and hence less pollution
- Better feed conversion ratio (FCR=feed given/fish weight gain)
Feeding regime The amount of feed given to carp depends upon several factors such as species, size (spawn, fry, fingerling, adult/brood), natural food present in pond, water quality parameters etc. To reduce feed wastage, feeding should be monitored; otherwise it will lead towards deterioration of water quality, which in turn causes stress, disease and/or mortality in fish. The proper feeding schedule should be followed throughout the carp culture
Figure 1. Different feed ingredients, pelletizers, feeds and feeding methods for carps
Table 3. Feeding schedule followed in different phases of carp culture practices*
|Different stages of fish||Feeding schedule|
|Spawn to fry (Culture period 15 days)||First week: 4 times of initial body weight (BW); Second week onwards: 8 times of initial BW in finely powdered form.|
|Fry to fingerlings (Culture period 90 days)||First month: 6-8% of fish body weight (BW); Second month: 5-6% of BW; Third month: 3-4% of BW in dry pellet form.|
|Grow-out culture (Period 10-12 months)||First month: 3-5% of BW; In the subsequent months: 1-3% of BW provided in dry pellet form.|
Feed for the grass carp fish: Grass carp should be fed with green fodder-barseem, Azolla, duckweed etc. @ 4-5% of BW. Care should be taken while feeding that, grass carp should be fed first, so that the dry feed remains available for the rest of the fishes.
Feeding frequency and time: Adults and fingerlings are fed twice a day, whereas, the spawn and fry are fed 4-5 five times/day. Fish should be fed preferably twice a day, in early morning after sunrise and in the evening before sunset.
- Broadcasting or hand feeding (Fig. 1h): Broadcasting or hand feeding is the most common method of feeding in semi-intensive culture. Though it is the most convenient method of feeding, it leads to feed wastage.
- Bag feeding (Fig. 1i): In this method, feed is kept in perforated gunny bags and is suspended in the water column at different places in the pond. The feed bags are dried properly every alternate day so that fish don’t get infected with pathogenic microorganisms (bacteria, fungus etc.). But, there is substantial loss of feed and nutrients in this method.
- Frame feeding for grass carp (Fig. 1j): Surface floating feeding frames (PVC or bamboo) is used to feed grass carp with green grasses-Barseem, Azolla, Duckweeds etc.
In order to prevent the loss of feed and keep the pond ecosystem clean, following methods are used for feeding during different stages of fish
- For spwan and fry : Powder feed broadcast
- For fish fingerling/adult fish : Feed balls (doughs)/pellets (floating or sinking)
Food conversion ratio (FCR)
In supplementary feeding, the FCR is an index, which helps the farmer to know whether his crop has been economical or not. This ratio is calculated between the feed given to fish and weight gain in terms of fish growth. For e.g., during a culture period, if 1000 kg feed was provided to produce 1000 kg fish the FCR is 1:1; or in other words, for producing one kg of fish, one kg of feed is required. Farmers should have the knowledge about standing crop and its growth and survival rates to calculate FCR, which can be improved carefully by feed monitoring and pond management.
Key points to remember
- During feeding, observe your fish carefully to see how actively they eat. A good appetite is a sign of good health and good water quality.
- Every 15 to 30 days, check the fish weight gain and adjust the daily feeding ration accordingly.
- Feed should be always given at a fixed amount and at a fixed place.
- Feed should be stored in cool, dry, well ventilated room to avoid losses due to spoilage.
- Fingelings/adults should be fed twice a day in two equal installment, while spawn/fry should be fed 4-5 times/day.
- In case of disease problem in ponds, feeding should be stopped with immediate effect.
Feeding should be stopped during overcast conditions, while in winters it should be reduced/stopped gradually.
( Authors are assistant professor and scientist at the Department of Aquaculture, College of Fisheries, GADVASU, Punjab respectively. References used for this article can be provided on request. Views expressed are personal.)