A proper selection of brood fish is one of the most important aspects to obtain greater results in breeding and grow out. In general, farmers select the fast growing and largest fish on the assumption that these characteristics will be inherited by the progeny. However, it is not recommended to choose their offspring or same stock, as this results in inbreeding and poor growth rate and a significant number of deformed fry. To the extent possible, the brood fish should be selected from the different sources.
A minimum of three months before the breeding season the male and female fish has to be separated from the regular culture tank to avoid the unwanted breeding. During segregation, it is important to avoid stress while netting. Male and females can be identified through secondary sexual morphological characteristics, which develop during the season of reproduction. In males, the milt runs freely when abdomen is gently pressed and the females have a swollen abdomen due to the development of ovaries. The fishes have to be maintained with sufficient space and need to be fed with a protein-rich feed which improves the gonadal development and also produces high quality eggs.
The following Table provides the secondary external morphological of Indian major carps.
|1||Scale, Operculum, and pectoral fins||Rough to touch, particularly the dorsal surface of pectoral||Pectoral smooth to slippery|
|2||Abdomen||Round and firm||Swollen and soft|
|3||Genital opening swollen||Elongated slit, white in colour, not swollen||Round and pink|
|4||When pressure applied on abdomen opening||Milky white fluid oozes through genital opening||A few ova may ooze through genital|
|5||Shape of body and size||Body linear, swollen||stouter, slightly large|
Hypophysation refers to the breeding of fish with pituitary gland extract. Brazilians developed this technique. In India, H.L.Chaudhary and K.H.Alikunhi pioneered the use of this technology for Indian major carps. Induced breeding means to induce fish to release gametes through the application of pituitary extract or hormones or chemicals.
Induced spawning is conducted during the onset of the southwest monsoon season (June) where there is an accumulation of rainwater in ponds and also a small reduction in temperature. The common carp pituitary is considered for better results, but in most cases same species gland and Human Chorionic Gonadotropin (HGC) are used. The administered dose of pituitary gland depends on the maturity stage of fish, and environmental condition (rain and temperature). A primary dose of 1 – 2mg/kg and second dose of 6 – 8 mg/kg body weight of fish after six hours is administered. After injection, the brood fish has to be transferred into the breeding hapa following the ratio of two male for every one female. The breeding hapa is a box-shaped enclosure made using cloth. About 50,000 to 1,00,000 eggs are hatched in hapa of size 2 x 1 x 1 m. Facility to open and close the upper flap is also made available. The corners of the cloth in all sides are tied to poles to keep them intact. The bottom should not touch the ground. Water temperature is to be maintained at 26 – 31OC. Spawning occurs after 16 – 18 hrs and the hatchling fall into the outer hapa. The breeding regularly takes place after 4 – 6 hrs of the second injection. Due to the riverine habit of these fish, they spawn only once, unlike rohu and mrigal which have possibilities to spawn again after one or two months.
Newly hatched larvae nourish themselves for 3 – 4 days, after which they depend on the natural feed from the environment. Availability of natural feed is most critical during the phase when it changes from the yolk sac nourishment to the commencement of natural feed, besides a suitable ecology to obtain greater survival percentage. Adequate care is to be taken before initial stocking.
The nursery pond is a pond where spawns are reared into fry. It takes 15 – 20 days with a lower water depth of 1 m. Nursery pond size of 0.02 to 0.1 ha is usually suitable for small-scale production and 0.5 ha for large-scale production. For fry rearing the seasonal ponds are preferred than the perennial ponds. Also small ponds have greater scope in terms of effective utilization than larger sized ponds.
The carps spawn need to have good environmental conditions and food availability. Prior to release of the spawns, make sure there exist a congenial condition and adequate natural food organisms, which enhance the survival rate. A well prepared pond environment provides an optimum condition for a spawn. If its a drainable or seasonal pond, effective preparation include draining, drying, ploughing, liming, filling with water and fertilizer application. For perennial or undrainable ponds, besides the above mentioned steps, control of aquatic weeds and eradication of predatory and weed fishes are also to be take care of.
Pond drying and ploughing facilitate the oxidation of organic matter, degassing of Hydrogen sulphide and ammonia, kills the pathogenic microorganism, predatory and weed fishes and remove the unwanted aquatic weeds. Ponds should be dried for a minimum of 7 – 10 days or until the cracks develop on a clayey soil or until the stage when footprints do not form on a sandy soil.
The pond productivity depends on the soil quality of the pond, such as pH, water retention, texture, total organic carbon, available nitrogen and available phosphorus. Liming helps to improve the productivity by adjusting soil pH, mineralization of organic matter, release of soil bound phosphorus to water and disinfection of pond bottom. Liming materials include agricultural lime (CaCO3), dolomite (CaMg(CO3)2) and Calcium oxide or Quick lime (CaO). The quantity of application varies with its effectiveness and soil pH. Generally, 200 – 500 kg/ha is applied to pond soil. After application, the bottom of the pond should be ploughed well to mix it with the surface soil. The quick lime is preferred for application to the soil during initial preparation and agricultural lime is preferred for application after stocking the seeds. The optimum soil pH is is to be maintained at 6.5 to 7.0.
Poorly managed ponds are infested with emergent, floating, submerged, and marginal weeds. It reduces phytoplankton production (due to nutrient competition and prevention of light penetration), disturbs balanced oxygen availability (supersaturation in day and depletion in the early morning), provides shelter to predator fish and insect, reduces the living space, increases siltation, and obstructs netting and harvesting.
The aquatic weeds can be controlled by manual, mechanical, chemical and biological methods. The selection of the method depends on the pond size, extent of weed infestation, availability of time and money. Manual method is generally advocated for weed removal, because it is easier, less time consuming and cost effective.
Physical methods of weed control include manual removal, usage of Winch, Cono- weeder, Polythene shading, etc.
Chemical methods of weed control include application of Anhydrous ammonia @ 20 ppm, Glyphosate @ 3 kg/ ha, 2 ,4 – D (2,4-Dichlorophenoxyacetic acid) @ 7 – 10kg/ ha, Simazine @ 0.3 – 0.5 ppm, etc. .
Biological methods of weed control include usage of Plankton blooms, Floating Weeds, Macrophagus fish (grass carp, silver barb), Snails, etc
Eradication of predatory and weed fish
The presence of predatory and weed fishes in nursery affect the survival rate. These fishes normally spawn prior to onset of carp spawning and increase their population. The larvae of predatory may compete with carp seeds for food, space, oxygen, etc that affects the growth and survival rate. Thus, eradication of weed fishes (murrel, catfishes, puntius, barbas danio and anabas) is a prerequisite before stocking the carp seeds.
The dewatering and drying practices are best to remove the predatory and weed fishes. However, if dewatering is not possible, eradication can be done through the application of a pesticide. The selected pesticide should have characteristics such effective even on usage of low dose, does not affect the quality of the fish, rapidly detoxifies and economical and readily available.
The physical methods of eradication include drying, usage of hook and lines and repeated netting.
Certain derivatives of plant origin such as Derris root power, Mahua oilcake, Tea seed cake can be used.
Under the chemical method,
The successful fry rearing in ponds depends on the availability of zooplankton. For sustained zooplankton production availability of phytoplankton and bacterial base are important factors. Phytoplankton production requires adequate nitrogen and phosphorus. The nutrients can be added by organic and inorganic methods.
The organic manures are rich in carbon and contain a small amount of nitrogen and phosphorus. It promotes zooplankton growth by the saprophytic food chain. Cow dung and poultry manure are organic manures that are usually used. They are applied before 15 days of seed stocking at the rate of 5 – 6 tons/ha and 2 – 3 tons/ha respectively. The nitrogen and phosphorus are 2 – 3 times greater in poultry manure than cow dung manure. Hence half of the dose of cow dung is used when poultry manure is applied.
The inorganic fertilizers used are Urea or Ammonium sulphate as a source of nitrogen and Single or Triple phosphate as a source of phosphorus.
When the applied dose exceeds the limit, blue-green algae blooms. Thus, a mixed use of organic and inorganic fertilizer is recommended (750 kg groundnut or mustard oil cake, 200 kg cow dung and 50 kg of single super phosphate per hectare) for the sustained and rapid production of phytoplankton.
Prior to the transfer of the spawns to the pond, stocking acclimation has to be done to prevent sudden water quality changes, which affect the survival rate. Early morning or late evening is recommended for stocking. It may be noted that there may be lower dissolved oxygen in the early morning in the ponds, if the ponds are newly fertilized ponds and have high plankton. Similarly, in the evenings the water temperature may be high in the ponds that could stress the spawns. These parameters have to be tested and taken care of before stocking to obtain higher survival. A stocking density of 3 – 5 million / ha or 300 to 500 per m2 is recommended for earthen ponds and 10 – 20 million /ha or 1000 to 2000 per m2 for cement cisterns.
The availability of natural food is insufficient to rear the spawn in ponds due to higher stocking density. The requirement of artificial feed is hence necessary. Artificial feed comprises of groundnut oil cake and rice bran at 1:1 ratio. 6 kg/million/day of feed is required for the first 5 days. For the remaining period, 12 kg/million/day is requried. The two feed ration is necessary to get greater survival rate and enhanced growth rate. The prolonged rearing of spawn in the nursery pond reduces the growth and survival rate. After 15 days, the spawn may reach about 25 cm, which is suitable size for fingerlings rearing. Spawn can be harvested by using the gear with the mesh size of 1/8". It's measured with the perforated cup. Normally, 40 – 50 percent survival is achieved in well-practiced ponds. 2 – 3 crops are possible in earthen ponds and 4 – 5 crops are possible in cement cisterns. Monoculture is practiced for spawn rearing in ponds.
The ponds for the rearing of fingerlings also require all pond preparation practices like those followed for nursery ponds, except the insect control practices. Cow dung @ 3 – 4 tons/ha and single super phosphate @ 30 – 40kg/ ha are to be added in the fingerling rearing pond 10 days prior to stocking. In addition to this, after stocking, 500kg/ha cow dung and 10 kg/ha of single super phosphate are added two times in a month. Please note that only half the amount of Cow dung is to be added when poultry manure is applied.
Polyculture is practiced in the rearing of fingerlings based on feeding niche distribution. Commercially important species also can be reared along with carps. When the seeds are transported from longer distances, there is need for proper acclimation. The stocking size for about 25 mm size (15 days old fry) is a density of 0.1 – 0.3 million/ ha without aeration and 0.5 – 0.6 million/ha with aeration. For polyculture, the preferred ratio is 1:1:1 or 1:2:2 or 3:4:3 of Catla: Rohu: Mrigal.
Carp fry are planktophagic with preference to zooplankton. The stock has to be fed with supplementary food. Rice bran or wheat brawn mixed with groundnut oil cake / mustard oilcake / cotton seed oilcake in 1:1 ratio may be used for nutrition. To achieve greater growth, extra ingredients such soya flour, fishmeal vitamins, mineral mixture can also be included. During the first month, the preferred feeding quantity is about 8 – 10 percent of the body weight of biomass and during second and third month 6 – 8 percent of body weight is sufficient. A minimum of two-time feeding or two rations per day is desired.
Harvesting of fingerlings is done when it reaches about 80 – 100 mm length which generally takes around 2 – 3 months. Rearing of fingerlings duration can be extended when advanced size fingerlings are required. If the fingerlings are needed to be transported, the feeding should be stopped one or two days before harvest to improve conditioning. A minimum of 60 – 70 percent of survival is attained if best practices are adopted.
The ponds for rearing of grow out also require all pond preparation practices like nursery and fingerlings. The ponds are usually stocked with 30 – 40 percent of surface feeders, 30 – 35 percent of column feeders and 30 – 40 percent of bottom feeders. The fingerlings of 60 – 100 mm size are considered ideal for rearing in pond. When small size fishes are stocked higher mortality and poor growth performance occur in initial months. 50 – 100 g fingerlings are suitable for rearing in cement cisterns to realize a survival rate of about 95 percent.
Many studies have been conducted over the years to enhance fish production and raise the income. The recent trend in carp culture technology is that it has transformed from single stock multiple harvest to multiple stock multiple harvests. The single time stocking and single harvest with the stocking of 8000 fingerlings is termed single stocking and single harvest. Single stocking and multi harvest is, when the stocking density is more than single stocking by about one and half times. It is done with the intention to harvest 50 percent after 6 months. In multiple stocking and multiple harvest, the stocking density is the same as single stocking (8000/ha). The harvest can be done when fish reach 500g. After every harvest, the stocking is done to replenish the harvested number. The stocking number should be maintained.
In single stocking, with the ideal stocking density of 8000 fingerlings, a production of around 5 tons/ha/yr is realised in composite fish culture. In temporary ponds, with a stocking density of 10,000 – 12,000 fingerlings, the fish would grow about 300 – 400 g in 5 – 6 months. If bigger size is required stocking size should be more than 100 g with a density of 3000 – 4000. It can then produce around 1 kg fish in 10 – 12 months.
The cultural practices have evolved in the county to suit species selection, water availability, fertilizer dosage, feed usage, etc. The carp culture technology can be categorized into the low input, Medium and high input systems.
Food is the main governing factor in fish growth. Naturally available food is inadequate and thereby supplementary feed is necessary for enhanced fish production. Feeding preferably twice a day is advocated. Excess and under feeding should be avoided as both affect fish growth.
The fishes are sampled periodically to check the health of fish, including growth, presence of parasite and bacterial diseases. Carps in grow-out pond are likely to be infected by Epizootic Ulcerative Syndrome and Argulus infection especially in the winter season. This can be diagnosed using CIFAX at 1 liter/ha in water.
The physico-chemical parameters of pond water should be within optimum limits for better fish growth and survival. Water quality is not an issue for low stocking density and low yield harvest but is one of the major concern when the stocking density is higher. The dissolved oxygen is an important factor to be monitored. Dissolved oxygen, the source of which is from the atmosphere and also through photosynthesis by plankton and macrophytes, should be ideally about 5 mg/l. This can be maintained by using aerator (paddle wheel, aspirators and submersible pond aerator). The paddle wheel aerator is appropriate for ponds of depth 1 to 1.5m. The other two aerators have higher injection capacity of air into the water and hence can be used appropriately. A simple way of aeration is to circulate the pond water. It can be done using a pump which can take water from the lower surface of the pond and splash it into the same pond.
Fishes are harvested after 10 – 12 months in single stock and single harvest system and regular in multiple stock and multiple harvests. In one year culture, the catla grows about 1kg and Rohu and Mrigal grow about 600 – 700 g. When the fingerling stocking size is of 150 – 200g, a harvest of fishes weighing more than one kg is possible.