sewage fed aquaculture system

SEWAGE FED AQUACULTURE SYSTEM MR. MONJIT PAUL & MRS. MUKTI CHANDA

[email protected]

Sewage fed aquaculture system

Mr. Monjit Paul & Mukti Chanda

GLOSSARY: Batam cake: Local fish feed or nut oil cake. Bati: Vessel used for measuring quantities of hatchlings. Bheri: Earthen pond used for fish production. Dallal:

Agents

and

fish

availability/quality

informants

used

in

establishing and securing the transactions of fish of all life stages between two parties. Earthen hapa: Small shallow earthen pond used for holding fish. Golder: Trader who transports large quantities of fish seed by truck (owned or hired). Golder employee: Sometimes permanent but usually seasonal employees of golders involved in husbandry of fish seed during transportation in truck and from truck to purchasers’ facilities. Hapa: Nylon net cage used for holding fish. Mahua cake: Distillation residue of the fruit (Manileara indica) used as a natural pesticide in pond preparation. Hundi: Small aluminum vessel used for transporting fish (also known as patil in Bangladesh). Patil Wallah: Independent trader who transports small quantities of live fish and seed in hundies, usually on foot, bicycle / rickshaw or public transportation (buses / trains).

Asutosh College, Kolkata



INTRODUCTION: The fish farmers of Kolkata developed a unique technique of utilization of domestic sewage for fish culture long back in 1930s. The early inspiration of utilizing the sewage for fish culture emerged from the waste. Stabilization pond used as water source of vegetable fields. This technique is considered to be the largest operational system in the world to convert the waste in consumable product. The growing fish demand of the metro city Kolkata is widely met by this technique. In the course of time the area under sewage-fed fish culture reached up to 12,000 ha. But recently due to rapid and indiscriminate urbanization it has come down to 4,000 ha (approx) resulting in crisis of livelihood of rural people. There are appeals to Government to declare the existing sewage-fed aquaculture area as sanctuaries. However, even today, a considerable amount of fish consumed in Kolkata city is produced from this system. There are appeals to Government to declare the existing sewage fed aquaculture area as sanctuaries and to protect them from further encroachment by the rapidly expanding population of Kolkata city. The waste recycling system that has evolved in Kolkata city involves garbage based vegetable farms, wastewater fed fishponds, paddy fields using fish pond effluent and sewage fed brackish water aquaculture. The system is based on domestic sewage mainly and it is an extensive or semi intensive type of aquaculture. The farmers generally utilize treated sewage water to culture the organisms. No fertilization or feeding in the culture pond is practiced, because the raw sewage is nutrient rich and can enhance the growth of plankton production. The culture system is also integrated type with duck, hen, goat, pig or buffalo farming to meet the protein demand in the city. Production of vegetables and flower is also done based on the raw sewage.




OBJECTIVES OF OUR TRAINING PROGRAM This study was primarily undertaken to describe and analyze the current production of freshwater fish in West Bengal, India by wetland culture practices and its distribution within the state. Important objectives of the work were to assess current practices, trends and constraints within the system and to identify areas of improvement to enhance the prospects of its future sustainable development and to enhance our skills in the area of practical field. Industrial Fish and Fisheries is a part of natural science, which needs practical exposure. The study also help to improve the knowledge on fish culture practice, sustainable development of our state and also our country by fish production,

utilization

of

wetlands

for

protein

production,

and

improvement of socio-economical condition of the weaker sections of the community (fish farmers) through cheap and semi intensive methods of fish farming by organizing a cooperative society. We gather all the knowledge about the above, but theoretically all the college lectures, but it is not enough for natural science. So at the end of 3rd Year we gather knowledge about them practically. This training program also helps to give the idea about the culture method by simple applied theory. The wetland culture practice is the unique feature of Kolkata. The wetlands area to the east of Calcutta is a large consumer of fish seed and makes a significant contribution to food-fish supplies for local city and rural populations.




PURBA KOLKATA MATSYAJIBI SAMABAYA SAMITY LTD. The “Purba Kolkata Matsyajibi Samabaya Samity Ltd.” is one of the cooperatives started in 2005 with the support of the government. The society is situated in Eastern Kolkata, Tiljala, in South 24 Parganas behind the building of Ruby Hospital and Srachi Tower (Emami Tower). This society is formed by the weaker section of fish farmer who can not earn by investing their own money. The Society has 120 members with 3 female members. A Management committee consisting of nine members manages the Society. Elections are held once in three years. The Secretary of the Society can work in that position for only 3 years. This demonstrates the high-level of confidence created by the leaders through their completely transparent system of management and provision of equal benefits to all members. Every member of the society takes part actively in the work and activities of the society and thereby conflicts are avoided. The Society owns water area covering about 48 ha or 360 bigha of land, with total number of 108 ponds. The society has 28 nursery pond and 80 stocking pond. The Society has a number of assets like nets, boats and trucks, which are required for the efficient operation of the farm. The farm earns Rs. 10,000/day. Each member receives a financial benefit of Rs. 2,000 - 2,500 /month or Rs. 80/day along with a weekly paid holiday, annual festival bonus and special holidays. Members are also given limited medical reimbursement facilities. The annual transactions of the Society are large in magnitude with financial transaction. This is a huge sum in the local context and there is lot to learn from these successful cooperatives. The Society uses its own labor force for harvesting fishes and marketing them in live condition. Several aquaculture management practices are adopted by the Society.




The major expenditure of the farm is on some sewage fed farms also integrate with pig farming, goat farming, buffalo, duck farming and hen farming. Though due to the bird flue disease outbreaks in recent days, the duck and hen farming is avoided. The farm is also integrated with horticulture and vegetable culture. The

sewage

fed

system

is

threatened

by

the

increasing

urbanization. Note the multistoried commercial complexes behind the fish ponds. Procurement of seeds from hatcheries since the farm produces only common carp and tilapia seed on site. Fish are harvested continuously almost three times everyday throughout the year, except for a month break in the whole year.




The Farm (Purba Kolkata Matsyajibi Samabaya Samity Ltd)




CHAPTER I: SEWAGE: Definition of Sewage: Sewage is defined as a cloudy fluid arising out of domestic, municipal and industrial waste, containing mineral and organic matter in solution or having particles of solid matter floating, in suspension, or in colloidal and pseudo-colloidal form in a dispersed state. Sludge differs from sewage in that it is the solid portion of waste and does not include fecal matter urine. Fish and Sewage: Wastes, including sewage and waste water produced by human community hold high potentials for boosting fish production. The usual high density of plankton and consequent die-off in sewage water ponds is controlled and water quality improved by stocking with fish which graze upon and utilize the dense plankton population in such ponds. Thus, increasing importance is recently being given to enhance aquaculture production through sewage utilization. Very high productions have been obtained in India. Composition of sewage: Sewage may vary considerably in composition and strength from place to place. The strength of sewage is determined by the amount of O 2 required to oxidize completely the organic matter and ammonia present in it. There is also variation in composition between domestic and industrial sewage, the later containing more pollutants in terms of heavy metals and bacterial load and other toxic ingredients. While the sewage is very rich in anaerobes when it is raw but gradually transforms to an enriched freshwater when it undergoes treatment. Sewage contains living matter especially bacteria and protozoa. The water content of sewage may be 98 – 99.9 %, rest being dry solid matter. Domestic sewage has been reported to




contain about 250 – 400 ppm of organic carbon and 80 – 120 ppm of total nitrogen, thus giving the C and N ratio of around 3:1. Common characteristics of Kolkata city (raw) sewage: pH: 6.8 – 7.8, CO2: 10 – 140 ppm, Dissolved O2: almost zero, Total alkalinity: 170 – 490 ppm, Nitrates-N2: 0.01 – 0.6 ppm, Nitrite- N2: 0 – 0.08 ppm, Free ammonium- N2: 12 – 63.6 ppm, Albuminoidal ammoniumN2: 1.1 – 16 ppm, BOD: 100 – 500 ppm, Phosphate (as P2O5): 0.12 – 14.5 ppm, Suspended solids: 160 – 420 ppm, Settle-able solids: 1.6 – 2.8 ppm, Organic Carbon: 24 – 88.8 ppm. Gases like CO2, H2S, and NH3 etc. are in dissolved state. The raw sewage is detrimental to fish and to make it suitable for aquaculture or for usual disposal to the river, treatment is necessary. TREATMENT OF SEWAGE: 1.

Primary treatment: This is mostly the physical removal of solids by mechanical means. The solid material is removed by screening (for larger

coarse

particles),

skimming

(for

floating

solids)

and

sedimentation (for suspended particles whose density is greater than that of liquid) techniques. 2.

Secondary treatment: Soluble organic and inorganic matter, namely the carbohydrates, proteins, fats, hydrocarbons and other nitrogenous materials

which

are

degraded

mostly

biologically,

using

microorganisms into the smaller constituents i.e. CO2, H2O, NO3, NO2, SO4, PO4 etc. which can be easily disposed. Sometimes chemical and physical removals of substances are combined with this to increase the effectiveness. There are three basic methods for secondary treatments: activated

sludge

(flocculation),

biological

filtration

and

waste

stabilization. In the activated sludge or flocculation process, the sewage is aerated by diffused air or by mechanical means. The activated sludge (or biological floc) contains the microorganisms that remove the soluble and insoluble organic matter in the sewage by a




combination of adsorption and oxidation or assimilation. Aeration supplies the sludge microorganisms with oxygen and keeps the floc in suspension. After a suitable contact time (1 – 20 hrs) the sludge is separated from the sewage effluent in a settling tank. Some of the settled sludge is returned for aeration along with new sewage but most of it is treated separately in a sludge treatment plant. 3.

Tertiary treatment: This is biological and chemical removal of soluble products of partial or complete oxidation. For example, removal of NO3, NO2, SO4, PO4 etc.

4.

Quaternary treatment: Physical or chemical removal of refractory organic or other substances which may be unpleasant and even toxic. Chemical treatment comprises of (a) Coagulation or chemical

precipitation (e.g. by alum) (b) Deodorization (by Cl2, FeCl3) and (c) disinfections or sterilization (by Cl2, CuSO4, liming etc.). The process generally adopted for the use of sewage treatment before release in fish ponds are: (1) Sedimentation (2) Dilution and (3) Storage (1) Sedimentation: The function of sedimentation is to remove suspended solids from sewage to the maximum possible extent. It is done by letting sewage into a pond/tank at a high velocity of flow. Sedimentation results due to sudden drop in velocity when sewage enters a large pond from sewage channel. Sedimentation is best carried out by in two successive stages i.e. primary and secondary. The primary stage is intended to settle down most of the heavier solids while the secondary stages serve two purposes: (a) Provision of additional period to help to mix and homogenize variations in the flow and (b) Promotion of natural purification process. It has been estimated that about 33% BOD is got rid of by sedimentation process, which may effect with 90% settlement of suspended solids and about 25% reduction in albuminoid ammonia.




(2) Dilution: Before introduction of sewage into any fishery its dilution by freshwater should be so effected that a positive dissolved oxygen balance (1:1 or 1:2) is maintained and the concentration of unwholesome ingredients such as CO2, H2S, NH3 etc. kept below lethal limit. The oxygen required for biochemical reaction is obtained from fresh water used for dilution and through green algae, and other vegetation in the water body. Sewage is stored here for few days. (3) Storage:

The biological processes carried out by microorganisms

present in the raw sewage oxidize it. Use of oxidation ponds (waste stabilization ponds) for sewage-fed fish culture has been suggested by many several workers. The term waste stabilization ponds is applied to a body of water artificial or natural employed with the intention of retaining sewage or organic waters until wastes are rendered inoffensive for discharge into receiving waters or on land through physical, chemical and biological process (self purification). This pond is suitable in India because of plentiful of sunshine. These are also cheap to construct and easy to operate. Organic matter contained in the waste is stabilized and converted in the pond into more stable matter in the form of algal cell, which find their way into the effluent. These ponds are of three types: a. Anaerobic ponds: It is pretreatment digester and requires no dissolved oxygen. These are designed to take on higher organic loading so that anaerobic condition prevailed throughout the pond. Such ponds are 2.5 – 3.7 m deep. Ends products are CH4, H2S, and NH3. b. Aerobic ponds: These are shallow, depth is 0.3m or less, so designed that growth of algae through photosynthetic action is maximized. Waste material is stabilized through microorganisms only and aerobic condition is always maintained. Ends products are CO2, H2O, NO3, SO4, PO4 etc.




Sewage Canal

Sewage Treatment (Mechanical Process)

Biological Treatment of Sewage




c. Facultative ponds: These are 0.9 – 1.5 m deep and are aerobic during day hours as well as for some hours at night. Only for few remaining hours of night, bottom layer become anaerobic. Aerobic, anaerobic and facultative may all be found in a facultative pond. In India, most of the waste stabilization ponds are of facultative type. The village ponds and natural depressions in rural areas are example of waste stabilization ponds. A conventional oxidation pond retains the settled sewage at a depth of 1 to 2 m (facultative ponds) for a period of 25 to 30 days. This pond contains the algal-bacterial cultures, which oxidizes the organic matter into CO2, H2O, H2S, NH3 and other decomposition products that are used as nutrients (e.g. NO3, SO4, PO4). If this type of ponds are designed well and operated effectively, well over 90% of the BOD is removed and the micro flora is much reduced. Simple Flow Chart of the Treatment of sewage:

Fish Culture with Sewage




Sluice Gate to prevent the entry of wild fishes and prevents the escape of cultured fishes in pond

Open channel through which sewage is flown in the pond.




Draining of Pond by pumping

Drying of Pond

Silt is removed at least once in three years




Aquatic Weeds (It can be used as biological filters)

Dried water hyacinth is kept in heaps in the ponds for decomposition (manuring)




CHAPTER II: SEWAGE-FED SYSTEM: The sewage fed ponds, which are locally called “Bheries”. Although these sewage-fed ponds are generally shallow and vary from 50 cm to 150cm in depth. This system covers some 3000 hectares and comprises of 154 fisheries (bheries) which produce 13000 tonnes of food-fish per year, of mainly IMC and tilapia, which are sold in nearby Calcutta markets, representing 16% of fish sales in the municipality (Bunting et al., 2001). The environmental ‘setting’ and system utilized for production in the ‘East Calcutta Wetlands’ is quite unique; fisheries utilise some 550000m3 of untreated wastewater per day (Edwards & Pullin, 1990), of primarily fecal polluted surface water and sewage water from Calcutta, via canals and a series of tributary channels. These wastewater nutrifies ponds, enhancing natural phytoplankton, zooplankton and benthic fish food sources, having economic benefits. Despite this input, inadequate wastewater supply has been identified as a limiting factor (Bunting et al., 2001) with 15% of bheri owners perceiving it as a problem (Kundu, 1994). Authority control over wastewater distribution to the wetlands, pumping station maintenance problems and sluice gate operation regulation problems result in unpredictable sewage supplies, (Bunting et al., 2001) which are compounded by the siltation of urban drainage systems and lead to competition between those exploiting the resource (Kundu, 1994). Species Cultured: Although both Indian and exotic carps are grown, farmers have specific preference for the Indian carps, namely catla (Catla catla), rohu (Labeo rohita), mrigal (Cirrhinus mrigala) and bata (Labeo bata) with bulk of the stocking consisting of mrigal. Exotic fish like silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon idella) and common carp (Cyprinus carpio) are stocked as a small percentage.



However,

the

popularity


of

tilapias

(Oreochromis

niloticus

and

O.mossambicus) is increasing and they constitute 5-30% of the species stocked with different ponds. There is also a tendency for some farmers to stock Pangasius hypophthalmus to control mollusc populations and some are attempting to culture high value species like giant freshwater prawn,

Macrobrachium rosenbergii. Culture Technique: The fish farmers of Kolkata operating sewage-fed fish fisheries, however generally use raw sewage, relying on intuition and experience for regulating its application. This practice is not only unhygienic but also harmful since the sediment organic matter besides raising the bed level of pond being highly oxidisable in character may undergo decomposition and cause negative oxygen balance causes mortality. But sewage partly or fully decomposed contains a high percentage of nitrogen, phosphorus, Ca, K etc. These nutrients together with adequate alkalinity contribute largely to a high productivity in sewage water and for this reason fertilization of fishpond is sometimes carried out with raw sewage.

Channel feeding bheries with slick of black sewage, just discernible




The following techniques were adopted by the farmers: 1. Preparation of ponds 2. Primary fertilization 3. Fish stocking 4. Secondary fertilization 5. Harvesting of fish Preparation of Ponds: Pond preparation is undertaken generally in winter (Nov – Feb) when the fish growth is reported slowest. Ponds are drained, desilted, tilled and dried in sun. Sewage from the canal is drawn in to the pond and allowed to stabilize for 15-20 days. The liming is also done in this stage to control the pH of the bottom soil and as well as to destroy the pathogens. Lime also helps to improve the growth of the fishes. Lime is applied in the pond by checking its pH. If pH is lower than 7, 50 to 80 kg of lime is often used in one bigha pond to improve the pH. The pond dikes are consolidated. Silt traps (perimeter canal along the dikes) 2-3 meter wide and 30-40 cm. deep are dug, as they get filled during regular harvesting of fishes. There are about 100 plant species which have been recorded in and around

the

East

Calcutta

Wetlands.

These

include

Sagittaria

montividensis, Cryptocoryne ciliata, Cyperus spp., Acrostichum aureum, Ipomoea aquatica, Typha spp., etc. Aquatic weeds as water hyacinth (Eichhornia), algae, Ipomoea, duck weeds (Lemna) and algae with other aquatic weeds are grown in the pond, though they can save the dikes from wave, and give shelter to fishes against high temperature and poaching and above all it extracts heavy metals from the sewage, supplies oxygen by photosynthetic

activity,

the

weeds

must

be

removed

for

better

management of the farm. The weeds are removed by manually (hand




picking) or by weedicides like 2-4D and detergents. Biological control of aquatic weeds is also practiced by extremely herbivorous fishes. For raising carp seed, ponds are dewatered completely during summer to remove all the carnivorous and weed fishes. When complete dewatering is not possible treatment with mohua oil cake (distillation residue of the fruit (Manileara indica) used as a natural pesticide) in pond preparation or other similar fish toxicants are used. The oil cake turns the water black, but after a few days the water become clear and residue of the oil cake acts as the fertilizer of the pond. The bamboo sluice gate is repaired which helps to prevent the entry of unwanted fishes and escape of cultured fishes. Primary fertilization: After pond preparation, sewage is passed in to the pond from the feeder canal through bamboo sluice. Initial fertilization of pond is done with the introduction of fresh sewage effluent, which is taken into the pond up to 90 cm. It is left to stabilize for 15 – 20 days. The self-purification of sewage takes place in presence of atmospheric oxygen and sunlight. When the water turns green due to photosynthetic activity, the pond is considered ready for stocking. Generally external fertilization is not used in the sewage fed farming system. But the mohua oil cake acts as the fertilizer in the pond when utilizes. The nutrients present in the sewage water are enough to fertilize the pond and helps in the production of sewage. Following this the ponds show extreme diurnal fluctuation of dissolved oxygen ranging from super saturation stage at day time to serious depletion in night. However, due to dilution and natural putrefaction process, the wide fluctuation of dissolved oxygen is minimized within a month and the pond rendered suitable for stocking and rearing fish seed.




Fish stocking: The photosynthetic activity in the pond is the basis for biological purification of the sewage. Once the water turns completely green, stocking of fish is initiated. Before stocking fish, some are kept in hapas in the pond to test pond condition through survival. If the results are positive, large scale stocking is undertaken. Fish stocking takes place several times in a year depending on the intensity of operation. All the species of Indian major carps e.g. Labeo rohita (Rohu), Catla

Catla,

Cirrhinus

mrigala

Hypophthalmichtys molitrix

(Mrigal)

and

Exotic

carps

e.g.

(Silver carp), Ctenopharyngodon idella

(Grass carp), Cyprinus carpio (Common carps) are preferred to be stocked but the percentage of Mrigal is kept greater and that of exotic carps is lesser. The popularity of Tilapia and fresh water prawn, Macrobrachium

rosenbergii is increasing these days. Pangasius hypophthalmus is also stocked by some farmers to get rid of mollusks. As the sewage contains high content of nutrient, the farmers keep very high stocking density, i.e. 40,000 to 50,000 fingerlings/ha. Sewage-fed ponds are used for raising seeds of Carps and Tilapia and also culturing them to table size The stocking density in such pond varies from 70000 to 150000 per ha. The density is depended mostly on the size of the spawn or fry. The preferable stocking density of the pond is Catla 40% 72 mm/ 6 gm 133 mm/ 30 g, Rohu 6% 72 mm/ 5 gm 147 mm/ 37 gm, Mrigal 45% 74 mm/ 4 gm 126 mm/ 24 gm, Common Carp 9% 54 mm/ 3 gm 135 mm/ 50 gm. For raising Tilapia seed more or less the same techniques as that of carp seed are adopted. However, instead of Tilapia spawn/fry, adult

Tilapia of both sexes is stocked together in the ration of 6 males: 4 females at about 20 000/ha. They bred profusely in the pond. The harvesting of fingerlings is initiated two months after stocking of adults and is continued periodically either fortnightly or monthly depending on the




density of harvestable size tilapia. Normally 30 – 40 gms Tilapia are harvested. Tilapia was not found to be affected even at the highest attained NH3-N level of 5.43 ppm. He got the production of 9350 kg/ha/yr Secondary Fertilization: After stocking, sewage is taken in ponds throughout the culture period at regular intervals @ 1–10% of the total water volume of the pond. In bigger ponds, water level is maintained by continuous inflow and out flow. The requirement of sewage is determined by observing the water color, transparency, temperature and depth. The sewage partly or fully decomposed contains a high percentage of nitrogen, phosphorus, Ca, K etc. These nutrients together with adequate alkalinity contribute largely to a high productivity in sewage water and for this reason fertilization of fishpond is sometimes carried out with raw sewage. Fish Harvesting: The bheri farmers have evolved rotational cropping system to maintain the supply to the market. Fishes are stocked and harvested throughout the culture period leading to periodical stocking and regular harvesting. After completion of one phase, fishes are restocked @ 1 Kg fingerlings per 5 kg harvested fish. Another harvest phase starts after 15 days of restocking. Generally, drag nets are used for harvesting by encircling technique. Some fishes like Tilapia and Common carp require hand picking technique for their harvesting. Specialized fishermen are employed in fishing.

Cyprinus carpio




Netting Operation

Netting Operation

The Fish after Netting




CHAPTER III: FARM MANAGEMENT: Rationale Cropping System: Farmers have evolved culture systems that are responsive to market demand. Fish are stocked and harvested throughout the culture period leading to periodical stocking and regular harvest. In larger ponds, harvesting takes place continuously for almost fifteen days in a month. After completion of one cycle of harvest in a large pond, fishes are restocked at the rate of one kg of fingerlings for every five kg of fish harvested. After restocking, fishes are left undisturbed for the subsequent fortnight and harvesting will start again after that period. Drag nets are commonly used for harvesting fishes through an encircling technique. However, for the bottom burrowing and difficult to catch species like common carp and tilapia, encircling with the net and hand picking are adopted as common techniques. There are specialized people to harvest fishes using these strategies. Health Care: The sewage-fed cultured fishes are most vulnerable to bacterial diseases, but surprisingly the occurrence of bacterial or any other disease is not common in sewage-fed fish farms. Even when EUS was prevailing in recent years in other areas, the sewage-fed ponds were uninfected. According to the farmer the diseases is vulnerable only in hygienic water. When the diseased fish released in sewage pond, the disease is automatically cured. However, parasitic infections by Lernea (Anchor worm) and Argulus (Fish lice), bacterial disease like fin rot or tail rot, fungal disease like gill rot and skin ulcer are common but they are not given any proper treatment. Fin rot tail rot gill rot or ulcer is common but theses diseases are not creating any problems.




Generally there is no disease management is taken in the culture pond. Liming is done periodically which can cure many diseases. But the treatment of disease should be taken in the farm for better management. Protection of Dykes: Aquatic weeds like water hyacinth are grown along pond dikes of larger ponds to break waves and prevent damage to dikes. In addition, these weeded areas, provide shelter to fish when the temperature rises, prevent poaching of fishes to some degree and most importantly serve as filters to extract nutrients and metals from the system. When these weeds grow in excess, they are periodically harvested and decomposed in the pond to enhance fertility of water. Surrounding these large ponds, silt traps 2-3 m wide and 30-40 cm deep are dug. These get filled with regular harvesting of fishes. Farmers restrict themselves to cleaning of these silt traps instead of digging the entire pond. Silt rich in nutrients is used for various purposes, including strengthening of dikes. Feeding of Fish Generally the feeding of fish is not practiced in extensive type of sewage-fed fish culture system. But in semi intensive type culture system, feeding is practiced with Mastered oil cake, Rice bran with 1:1 ratio. Nut oil cake, Coconut oil cake are also used. The nursery pond fishes are fed with wheat flour. The herbivorous fishes are fed with aquatic vegetation, aquatic weeds like

Lemna etc. In pond, the waste food products like residues of human foods, breads are also utilized. These foods are very good for Tilapia niloticus and

Tilapia mossambicus. The waste foods are taken from the hotels and nearby bakery.




Mohua Oil Cake

Unknown Fish may have the Aquarium Importance

Algae in Pond




Clearance of Weeds




Different Types of Aquatic Weeds




CHAPTER IV: NURSERY SYSTEM: The seed of the fish species are brought the bheri from the outside markets, but the nursery rearing of the seed is done here. A nursery is a facility where fish seed (spawn, hatchlings or fry) can grow. Efficient fishpond culture requires special preparation of nurseries for receiving spawn and hatchlings. The ideal size of a nursery is 0.02-0.05 ha with a depth of 1.0-1.5 m. Fish Seed Supply: Few independent nursery operations are present in the wetlands which supply the bheries as the present bheri have their own nursery ponds for rearing hatchlings and fry to fingerlings for stocking. Hatchlings, fry and fingerlings are therefore distributed to the wetlands to facilitate the needs of the producers. The system utilizes large quantities of seed to support the scale of food- fish production, which are primarily supplied by golders. Most of the supply, which includes all life stages, comes from hatcheries and nurseries in Districts to the north of Calcutta through golders based in the wetland village markets, Chowbaga, Chingrihata and Bantala who liase with dallals within production areas. Additional supplies of hatchlings were identified to come from Bankura District hatcheries through two golders based in Sealdah in Calcutta. Using hundies in trucks and operating on a daily basis from April to July these golders supply an estimated 240 million hatchlings to the wetlands. Local patil wallahs make an additional small contribution to wetland seed supplies. One patil wallah who was interviewed in the wetlands collected fish seed from Naihati Seed Market and by using the train and bicycle delivered fingerlings to Bamamghata Market in the wetlands. This particular market was chosen by the patil wallah as the absence of golders reduced competition, whilst being a fish market where producers sold




food- fish, offered opportunity for marketing and selling seed. Splashing was frequently done to aerate the water prior to sale whilst the placement of fish in a hapa in a nearby pond aided survival in the event of a delayed sale. Preparation of Pond for Nursery: 

Remove all aquatic weeds or Drain and dry the pond.



Apply 5-6 kg lime/200 m² which helps release food nutrients available and kills pathogenic organisms in the pond.



Refill the treated sewage water rich with nutrients. Generally no fertilization is done.



The water left to increase the plankton population. To determine if enough food organisms (plankton) for the fish fry have developed in the pond, the most basic and reliable test involves filtering approximately 50 liters of water through a fine mesh net or cloth into a 2.5 cm diameter specimen tube. Alternatively, a very simple field test in non muddy water is to dip one's hand in the water to the elbow. If the hand is no longer visible, the plankton is probably sufficient.



To kill the aquatic insects, oils are used. Sometimes diptrex are also used to kill the aquatic insects.



To enhance the plankton production, raw sewage may be given with required quantity to enhance the plankton growth in the pond water.



Stock 60,000-70,000 hatchlings/200 m² of 4-5 days age (200-250 g). The hatchlings should be of same age, uniform size, vigorous and released either in morning or late afternoon (day 30).




Fish Seed in Nursery Pond

Preparation of Nursery Pond

Bati used to measure the quantities of fish seed




Golders in Sealdah with hatchlings destined for the wetlands

Patil Wallah splashing to aerate hundi water




Aquatic Insects




Removing of Aquatic Insects by using of Oil & Soap

Insecticide




CHAPTER V: CULTURE OF TILAPIA IN THE BHERI The most common species are Tilapia (Oreochromis) niloticus and

Tilapia (Oreochromis) mossambicus cultured in the wetlands mostly. These species are popular because of their high resistance power in any condition of water, temperature and have good market value. The growth rate of the fish is also good and the fish is omnivorous. The fish is mouth brooders and can reproduce in any stagnant condition without any induction. Culture Procedure: Mixed Sex Culture: Mixed-sex populations of fry are cultured together and harvested before or soon after they reach sexual maturity, thereby eliminating or minimizing recruitment and over-crowding. A restricted culture period limits the size of fish that can be harvested. In mixed-sex culture, tilapia is usually stocked at low rates to reduce competition for food and promote rapid growth. One month-old, 1gram fry are stocked at 2,000 to 6,000 per acre into grow out ponds for a 4to 5-month culture period with total production is near 700 kg/acre for a stocking rate of 4,000/acre. Expected survival is roughly 70 percent. Two to three crops of fish can be produced annually in the tropics compared to only one crop in temperate regions. In temperate regions, mixed-sex culture is referred to as young-of-the-year culture because fry produced in the spring are grown to marketable size by autumn. Early spawning is needed to maximize the grow-out period. Male Mono-sex Culture Males are used for mono-sex culture because male tilapia grows faster than females. Females use considerable energy in egg production




and do not eat when they are incubating eggs. Male mono-sex culture permits the use of longer culture periods, higher stocking rates and fingerlings of any age. High stocking densities reduce individual growth rates, but yields per unit area are greater. If the growing season can be extended, it should be possible to produce fish weighing one pound (454 grams) or more. Expected survival for all-male culture is 90 percent or greater. A disadvantage of male mono-sex culture is that female fingerlings are discarded. The percentage of females mistakenly included in a population of mostly male tilapia affects the maximum attainable size of the original stock in grow-out. For example, manually sexed T. nilotica fingerlings (90 percent males) stocked at 3,848/acre will cease growing after 5 months when they average about 0.8 pounds (365 grams) because of competition from recruits. If larger fish are desired, females should comprise 4 percent or less of the original stock and predator fish should be included. The stocking rate for male mono-sex culture varies from 4,000 to 20,000/ acre or more. At proper feeding rates, densities around 4,000/acre allow the fish to grow rapidly without the need for supplemental aeration. About 6 months are required to produce 500-gram fish from 50-gram fingerlings, with a growth rate of 2.5 grams/day. Total production approaches 2.2 tons/acre. A stocking rate of 8,000/acre is frequently used to achieve yields as high as 4.4 tons/acre. At this stocking rate the daily weight gain will range from 1.5 to 2.0 grams. Culture periods of 200 days or more are needed to produce large fish that weigh close to 500 grams. To produce a 500-gram fish in temperate regions, overwintered fingerlings should weigh roughly 70 to 100 grams and be started as early as possible in the growing season. A stocking rate of 8,000/acre does require nighttime emergency aeration when the standing crop is high.




Stocking rates of 12,000 to 20,000/ acre have been used in 1.2 to 2.5acre ponds, but this requires the continuous use of two to four, one-horse power paddlewheel aerators per pond. Yields for a single crop range from 6 to 10 tons/acre. Poly Culture of Tilapia Tilapia is frequently cultured with other species to take advantage of many natural foods available in ponds and to produce a secondary crop, or to control tilapia recruitment. Poly-culture uses a combination of species that have different feeding niches to increase overall production without a corresponding increase in the quantity of supplemental feed. Poly-culture can improve water quality by creating a better balance among the microbial communities of the pond, resulting in enhanced production. The disadvantage of poly-culture is the labor intensive to sort the different species at harvest. The role of natural pond foods is less important in the intensive culture of all male populations and may not justify the expense of sorting the various species at harvest. Tilapia can be cultured with Indian Major Carps and as well as exotic carps. The carnivorous fishes like Murrells can be cultured with tilapia, which can grow by feeding of tilapia hatchlings and the over crowding also can be avoided. Male tilapia stocked at a rate of 800/acre yield nearly 770 pounds/acre when channel catfish are stocked at 3,000/acre. Silver

carp

(Hypophthalmichthys

molitrix), and grass carp

(Ctenopharyngodon idellus) at densities of 800; 1,000; and 20/acre, respectively can be stocked with tilapia for poly culture system with no additional feed. Another promising poly-culture system consists of tilapia and prawns (Macrobrachium rosenbergii). In poly-culture, survival and growth of tilapia and prawns are independent. Feed is given to meet the requirements of the fish. Prawns, which are unable to compete for the




feed, utilize wasted feed and natural foods that result from the breakdown of fish waste. Stocking rates for 1 to 2 gram prawns vary from 4,000 to 36,000/acre, but a rate of 8,000/ acre is often used to obtain a high percentage of market-size prawns (