The physical and chemical characteristics of the water of a pond are controlled by the structure of the basal soil, chemical characteristics and different mineral ingredients contained in soil. That is, productive capacity of any pond depends on the conditions of the basal soil of that pond. The characteristics of water influence the livelihood of the fish.

The Characteristics of Water

 The Characteristics of water are divided into 3 parts, such as..

1. Physical characteristics
2. Chemical characteristics
3. Biological characteristics


Physical Characteristics of Water

 The productive capacity of a pond can be ascertained by observing the physical condition of water. The physical characteristics are of following types

A. Depth of Water: 

Production of fish is hampered when depth of water is too deep or too shallow. When the depth of water of a pond ranges from 1.5 metre to 3 metre fish culture becomes profitable.


B. Clearness or Transperency of Water : 

If the water of the pond is muddy or opaque sunrays are obstructed to enter into water. As a result production of fish food is decreased. This hinders growth of fish. The productive capacity of a pond is increased when the transparency of water becomes 5 cm.

C. Temperature :

 The growth of fish is also dependent on the temperature of water. Growth of fish is less during winter and more during summer. For Rui(Carps) types fish temperature ranging from 25˚- 35˚ C is ideal.

D. Sunlight:

 The sunlight directly influences the production of natural food in the pond. If there are big trees on the banks of the ponds, the branches of the trees should be cut to ensure entrance of sunlight profusely into the water.

The floating water hyacinth, helencha etc. create obstruction to enter the sunlight into the water. These will have to be removed.

*fish


Chemical Characteristics of Water

 1. Dissolved Oxygen:

 Oxygen is essential for life. Oxygen released by the process of photosynthess by phytoplankton and aquatic plants is dissolved in, water. Some amount of oxygen from air is also mixed with water directly. The fish, aquatic plants and animals living in the water respire with the help of this oxygen. Oxygen is also utilized in the decomposition process of organic mater in the bottom of the pond. In order to maintain sustainability in the production of the pond presence of required amount of oxygen is essential. For successful, fish culture it is best to heve 5-8 mg of oxgen per litre of water.

2. Dissolved Carbondioxide:

 As oxygen is essentially required for life, so carbondioxide is also important for the preparation of natural food of fish. But if the amount of carbondioxid is increased somehow an action of poisoning develops. If the bottom of the pond contain more organic matter and clay mud then there will be excessive carbon dioxide when temperature become high. Fish production become good with the presence, of 1- 2 mg carbondioxids per litre of water.

3. PH Value :

-pH can determine whether the water is acidic or alkalin. Relatively alkalin water is congenial for fish culture. The pH of water ranging from 6.5 -8.5 is helpful for the natural production of food.


4. Phosphorus:

 The fertility of a pond depends on the presence of phosphorus. Natural water has only small amount of phosphorus. This phosphorus is converted into phosphates. Sufficient amount of phytoplanton is produced in the water in the presence of require amount of phosphorus.


Aquatic Plants and Animal lives of Water

 Generally aquatic plants grow in the pond. Some of the pond aquatic its plants and animals are small. Microscope is required to see these plants and animals. These small aquatic plants at animals are natural food of fish. Again some aquatic plants and animals create troubles for fish culture. The following aquatic plants and animals grow in the pond.


Floating Plants

 Leaves and stems of these types of aquatic plants float on water, but the roots hang in water Such as water-hyacinth, topa hyacinth, khude hyacinth etc. These hinders the entrance of the sunlight into the water and take the nutrients from the fertilizer used in the pond. As a result production of pond is decreased.


Submerged Plants

 These types of aquatic plants remain at the bottom of the pond. These hinder the entrance of the sunlight into the deep water and also create obstacle in the movement of fish. Such as leaf-sedge, thorn-sedge, nazas etc.

Deep Water Aquatic Plant 

Some aquatic pants have their roots in sides of the pond, but the stems and branches emerge and grow on water- Such as Arali, Dal, Kalmilata etc. Aprli plant resembles some extent to broadcast Aman plant. There are several types of Dals. These are familiar in different local names on the basis of regions of Bangladesh.
The smaller bio creatures of water, that is, small plants and animals of water are the planktons. Planktons are the natural food of the fish. The presence of sufficient plankton indicates good productivity of a pond. Planktons are of two types, such as

1.    Phytoplankton.
2.    Zooplankton

Phytoplankton:

 Small aquatic plant animals are called phytoplankton.They are green in colour. Phytoplankton's are natural food of fish. Such as-Diatom, Volvox, Spyrogyra etc. Excessive growth of phytoplankton hinders the certance of sunlight into the water of the pond.

Zooplankton: 

Small aquatic animals are called zooplankton. Such as-Daphnia, Rotifera etc Zooplanktons  are natural food of fish.


Insects: 

Different types of insects live in the water and clay mud at the bottom of the pond. These are the food of fish and included in food cycle. Such as-Grubs of water hopper.

Preparation of the Pond

 Fish culture is a cultivation process same as done in the case of crop production. As in the case of crop production, land is prepared by ploughing, irrigation, application of fertilizers etc. before plantation of seedlings. The pond has also to be prepared in the same process before releasing fish fries. The following steps will have to be followed in order to prepare a pond.

 1.     Pond excavation
 2.     Clearing out of weeds
 3.     Removal of voracious predator and unwanted fish 
 4.     Application of lime
 5.     Application of fertilizers
 6.     Observation of natural food of fish in water

Excavation or Repairing of Pond

 Excavation work of pond is the first step of pond preparation. The following are the excavation works of a pond  

Removal of Clay Mud.

 If there is excessive clay mud at the bottom of the pond, then there are possibilities of remaining poisonous gas. harmful bacteria and insects. In order to improve the environment of the pond 20-25 cm. of mud should be kept at the bottom and the excess or additional mud will have to be removed. The clay mud can be removed by drying the pond. 


Repairing of the Bank

 If the bank of the pond is broken, fish may be going out or the pond during rainy season and at the salne time unwanted and predator fish can enter into the pond which will ultimately create trouble for fish culture. For this reason the broken bank should be repaired during dry season and grass should be planted there. This will help to make the bank hard. The bank should be raised up to such height that it might not be inundated during flood. 


Clearing out Weeds 

The weeds extract nutrients from the fertilizers used in the pond and thus decrease natural food production of the fish. This hinders normal livelihood of fish. Weeds can be cleaned by the following methods. 


1. By Using Physical Labour:

 The floating and movable weeds, such as-water hyacinth, helencha, kalmilata, dal etc. can easily be revoved by using physical labour. 


2. Biological Method: 

After storing fish fries in the pond submerged weeds may grow. In order to control these weeds and make the environment proper the biological method is very appropriate. Grass carp and Rajputi lives on grass. If these fish are stored in ponds they can eat the submerged weeds and keep the pond environment.


3. By Using Chemical: 

Presence of excessive green algae in the pond creats hindrance to the livelihood of the fish. Fish may even die for want of oxygen due to presence of excessive moss or algae. Excessive green algae can, be controlled by using 35 gm of copper sulphate per decimal for 1 metre depth.


Removel of Predator and Unwanted Fishes

 The predator fish decreases the production of fish by eating the cultured fish fries and fish food. Shol, Gajar, Chital Taki etc. are predator fish. Predator and unwanted fish can be removed from the pond by the following 3 methods such as


1. By Drying out the Pond: 

After drying out whole water of the pond, the predator and unwanted fish can be removed by catching all fish. There are possibilities of remaining predator fish and harmful creatures in the mud by hiding. When the bottom of the pond is well-dried in the sun then the harmful insects and germs are killed and productivity of the pond is increased.


2. By Casting Net: 

When the water of the pond is less predator and unwanted fish removed by casting nets again and again. Net casting should be done slowly by tieing bricks or other heavy materials with the lower portion of the net.

3. By-Using Chemical Materials:

 it is not always possible to dry out a pond. Again by net caste also complete removal of predator fish, may not be possible. In such cases predator and unwanted fish and other harmful creatures, are removed by using chemicals like rotenon, phostoxin, bleaching powder etc.


Application of Lime 

Lime purifies the water of pond. It is essential to apply lime to the fish culture pond. Lime supplies essential calcium for fish. It decreases acidity of the soil and water and increases alkalinity. As a result it increases fertility of water and soil. Lime destroys harmful insects and germs of diseases.


The Doses of Lime Application: 

The dose of lime application depends on the existing organic matter of the soil. Such as, red and brown coloured soils are acidic in nature. In these types of soil lime should be used in more amount than normal doses.


Method of Lime Application :

Lime should not be spread directly to the pond.Quick lime is to be soaked with water in a pan or drum and when it becomes cold, it is to be spread though out the pond. Quick lime more effective than powdered lime.


Application of Fertilizer :

 Fish production depends on the production of excess phytoplankton, nitrogen, phophorus potassium etc. are requied. Water does not always have these materials. Besides these. the quantity of nutrient elements is decreased by fish collection,change of water and other natural reasons. That is why fertilizers are used to provide these necessary elements.

Fertilizer are of two types, such as 

1.    Organic manures 
2.    Inorganic or chemical fertilizers 

1. Organic manures :

 The manures derived from animals and plants are called organic manures.Such as cow-dung,excreta of poultry brids,compost,green manure etc. 

2. Inorganic or chemical fertilizers :

 The fertilizers manufactured in mills and factories by chemical procedures are called inorganic or chemical fertilizers. Such as- Urea, Triple super phosphate(TSP),Muriate of potash(M.P)etc. 

Doses of fertilizers in Pond : 

Doses of fertilizers depends on the characteristics of the soil and nature of the pond. for examples, ponds of sandy or clay types required more fertilizers than sandy loam soil.Again the old ponds have much- organic matters at the bottom, so they required less quantitity of fertilizers. But application of more fertilizer is required in case of newly excavated or reparied pond. 

Fertilizers are to be applied in two stages to the pond 

1. Fertilizers are to be applied at the stage of pond preparation before stocking of fish fries. 
2. Regular application of fertilizers are to be done after storing of fish fries upto collection of fish.


Method of fertilizer Application :

 Required quantity of fertilizer is to be kept in a pot and soaked with water three times than that of fertilizer during the previous evening. Next morning the soaked fertilizers are to be mixed with water and then to be spread to the pond. 

Testing the presence of Natural Food of Fish in Water: 

Water enriched with abundant natural food will show light green or brown colour. After 5-7 days of application of fertilizers water of the pond is to be kept in a transparent glass and placed in sunlight. If small green or brownish insect like granular materials are visible, it is to be ascertained that the water has got natural food. In this condition the pond becoms ready for releasing fish fries. 

Culture of Fries of Rui:

 The method of producing fries or fingerlings by releasing hatchlings are called fry culture or fry nursing. The pond where hatchings are released and reared upto fry condition is called nursery pond. And the pond where fries are nourished to produce fingerlings are called rearing pond. In our country generally fingerlings are produced by releasing hatchings. 

Management of Nursing Pond:

 The mortality and growth rate of fish fries in nursing pond depend largely or proper management: The improtant steps of this management, are described below


Selection of Pond: 

The size of the nursing pond should be 10-15 decimals. The bank should be raised. There should not be any tree on the bank. It would be, good if there are opportunities of drying out pond waters or supply of fresh water, the water bodies of small sizes having low depth of water during fry production season or during the whole year, can be used as nursing ponds. 


Depth of Water:

 At hatching stage the fries become very delicate, so if the fries are released to a pond of deep water they will die. For this reason the nursing pond should have a depth of 1-1.5 metre. 


Preparation of Pond : 

Preparation of pond includes making the pond suitable for living of the fries and managing necessary food production for the growth of the fries. The pond has to be prepared as discucssed earlier. Afterwards the harmful aquatic insect will have to be controlled. 


Control of Harmful Aquatic Insect:

 Before the hatching are released the pest aquatic insects are to be removed. These can be controlled by polling mosquito nets of small loops or the following chemical materials can be applied for complete eradication of the harmful aquatic insects. 

Aquatic insects can be controlled by the following method. 
1.     Dipterex
 2.     Kersoene or diesel 

Application of Dipterex: 

Dipterex is to be, applied of the rate of 35 gm per decimal for 1 metre depth of water. The required amount of dipterex should be mixed with water and then to be sprinkled throughout the whole pond 24 hours. mixed with water and then to be sprinkled throughout the whole pond 24 hours before releasing the fries. By way of doing this the harmful aquatic insects will be fully removed.

Supply of Supplementary Feed 

The fries are not fully nourished by natural food. For this reason supplementary food needs to be supplied daily to the frie in addition to the natural food. Fine rice bran, wheat husks, mustard oil cake, fish meal and blood of domestic animals can be supplied, as food.  

Examining Mortality and Growth Rate of the Fries

 With 7-8 days of stocking fries casting gunny-net should not be done. Onece after 810 days and then after every 10 days mortality and growth rate the fires need to be examined by casting mosquite net. 

Nursing 

When the colour of the water become excusive green or there is green layer on the top portion of the water, then supply of fertilizers and food should be stopped temporarily. If the management system as discussed is followed properly then the size of the fries will become 5-10 cm. (average weight 10 gms) within 2 months. Its ability rate can also be kept above 60%. Fries of this size are suitable for sale. As finger lings and can be released to stocking pond. 


Identification of Fries of Different Types of Fish.

 Rui:

 The body is some what elongated. Black round shapd spots, are present at the base of the tail. The margin of the fin is light redish. The upper lip is extended at the front and notched.

Katla :

 The head is bigger as compared to the body. Round black Katla spots are not present at the base of the tail. The dorsal, caudal and anal fins are of grey colour. He mouth is broad, the lip is thick but not notched.

Mrigel :

 The body is slender and elongated, There are rectangular black-spots at the tail base of the There are tape-like light black mark covering whole length of the body. The caudal fins are red colour, lips are equal and there is a barble. The mouth is curved downwand. 

Silver carp :

 It looks like chapila, The body is flat the colour is bright white and the fins are of grey colour. The dorsal fin is small. 

Common carp : 

The body is broad and of light golden colour. The dorsal fin is spread almost the dorsal tail. The head is small, the dorsal side of the fish is raised.There is a hard spine at the dorsal fin.There are two pairs of barble at the lips. 


Pisciculture at the Stocking Pond

 Pisciculture is a profitable investment. Different culture practices have be eveloped depending on the cultures of different regions, availability of inputs, knowledge about technologies and marketing facilities. The methods of pisciculture in ponds can be divided into three suchh as _ 

1.    Traditional method of pisciculture.
 2.    Semi-intensive method of pisciculture 
3.    Intensive method of pisciculture 



Traditional Mathod of Pisciculture

 In this method some fish fries are released in pond. Neither, fertilizer nor food are supplied to the pond. The fish maintains their liveligood by eating natural food produced at the fertility of the water and soil. No other nursing practices are done. 

Semi-Intensive Pisciculture

 Pisciculture by preparing pond properly, stocking fries on the basis of varieties and number partial application of fertilizers and supplying food occasionally is called semi-intensive pisciculture. In this method different varieties of fries are released in definite number in order to utilize the natural food at different layers. Fertilizers are applied in order to meet up the demand for natural food and more over some supplementary food are also supplied. 

Intensive Fish Culture 

The method of pisciculture by proper pond preparation, stocking of right number of healthy fries on the basis of varieties, regular application of fertilizers in order to supply sufficient natural food, supply of required quantity of supplementary food for balanced nutrition control of water characteristics and ensuring improved management practices is called intensive fish culture. It is aimed at achieveing more production form a pond within a shortest possible time. In this method fish production can be achieved to highest productivity of the pond by adopting appropriate technologies.

Mixed Culture of Carp Fish 

Rui, Katla, Mrigel, Kalibaush, Silver carp, Grass carp, Common. Carps are called carp fish. These types of fish eats foods from different layers of the pond. Fish of different varieties are cultured in a same pond in order to get increased production by completely utilizing natural food produced in different layers. This type of fish culture is called mixed culture. Fertile land, and water, sufficient sunlight, healthy fries, fertilizers, supplementary food and good nursing are required for successful pisciculture. 
The systematic steps for mixed carp culture are discused as under- 
1.     Selection of pond. 
2.     Preparation of the pond. 
3.     Stocking fish fries. 
4.     Application of fertilizer 
5.     Supply supplementary food  
6.     Appropriate nursing  
7.     Harvesting of fish. 

Selection of pond

 At the time of selection of the pond the things needed to be considered are plaec soil characteristics, depth of water, size volume, environment etc. During the selection of pond it is to be seen that the pond is very near to dwelling houses, this will help timely supply of food and fertilizers. Ponds ranging form 30 decimal to 1 acre of size are more suitable. There should not be big trees or bushes or shrubs on the bank of the pond. The leaves of big trees fall into the pond and spoil its water. Predators and other harmfu1 animals can live in the bush. Loam type of soil is the best for pisciculture. 

Preparation of pond

 For mixed culture of carp fish pond is to be prepared as per the method discussed earlier.  

Stocking of Fries

 Healthy strong fries are the precondition for increased production. Fries are to be stocked after growing sufficient natural food in the pond, Fries of 8-12 cm. are to be stocked in the pond. Of different varieties. of fries should be of similar size.

Application of Fertilizers 

After stocking fries fertilizers should be applied to the pond regularly or one day in a week up to the time of fish harvest in order to supply sufficient natural food in water.It is better to apply fertilizers everyday for getting increased production.This will incur less cost too. 

Supply of Supplementary

 Food The food supplied to the fish of the pond from outside is called supplementary food. Fish are not well-nourished by only natural food. For this reason fish is to be supplied with balanced food daily in measured amount. 


Process of Preparing Food :

 The measured amount of mustard oil cake is to be soaked in a pan for 10-12 hours. Then the soacked cake, bran and molasses are to be mixed together and small round balls will have to be prepared with the mixture. 

Determination of Quantity of Food :

 If there is sufficient natural food in the pond,then in case of carp fish,supplementary food is to be supplied at the rate of 3 percent of the total weight of the stocked fish of the pond.During winter 2 percent will be enough.

Method of Supply of Food :

 The required quantity of food is to be divided into two and to be supplied in the morning and in the evening . Food will not be wasted or spoiled if it is supplied at a definite time and in the definite place daily. Necessary food is to be kept in a basket or a earthen pot and will have to be hung under the water with the help of a bamboo stick. Food is to be supplied at different places at the same time. This will prevent competetion for food. 

Nursing or After Care

 To examine growth, health, and diseases of fish they are to be observed by net casting once in every month. The dissolved oxygen and carbon dioxide and phytoplankton and zooplankton in water are the controlling factors for aquatic environment. That is why their quantity are to be regularly observed. As discussed earlier, the amount of natural, food in water can be known by determining transparency of water: If 1-2 ml plankton is obtained by sieving through net 100 litres water. Then it is to understand that the pond has got enough natural food. 


Harvest of Fish 

Harvest of fish is an important thing of pisciculture. Fish grows rapidly upto a definite age. Afterwards although food consumption is gradually increased, but physical growth does not take place at that proportion. So timely fish harvest is of great importance. Rui, Katla, and Mrigel become 700 gm. to 1.5 kg. within 8-12 months. Silver carp, Mirror carp and Grass carp become 1-1.5 kg within 6-7 months. After 6-7 months of stocking of fries the big fish are to be caught and sold out. At the same time same number of fries of same variety are to be released to the pond. By this, increased production can be achieved. 

Some Problems of Pisciculture and their Remedies - Green coverlet on water

 When the water of the pond remains dark green for long time or develops a green coverlet on water, supply of food or fertilizers is to be stopped temporarily. These coverlets are developed for excessive natural food. When such coverlet is created fish may die for want of oxygen. 

Gasping of Fish 

Fish tends to gasp when there is want of oxygen in the pond. In this condition if the water is disturbed by bamboo beating or by swimming, good result can be achieved. The amount of oxygen can be temporarily increased by sprinkling water in the pond like a fountain with the help of a pump. The want of oxygen can be removed by applying potassium permanganet at the rate of 100 gm for 1 metre depth of water per decimal.


Examining Food Intake 

The places of food supply should be intermittently checked to become sure whether the supplied food has completely been consumed by fish. 

Muddy Water

 If the water of the pond remains always muddy fish production will be decreased. As a remedy 1 kg of lime per decimal is to be applied. The muddy problem can also be solved by keeping bundless of straw at a corner of the pond. 


Diseases of Fish

 Fish may be attacked by different diseases. Such as fin rot,lice,dropsy etc. Necessary treatment measures are to be undertaken after diagnosing these diseases. 


Culture of Shing and Magur

 Shing and Magur are very tasty fish. Their nutritive value is high. These fish has got great demand in the market for their taste and for wide use as diet of the patients. These are omnivorous fish. The food of shing and magur are larvae and pupa of insects and mites, zooplankton and decomposed organic matter. Shing and Magur are available in all the countries of South-west Asia and Africa including Bangladesh. In our country Magur may be 30-45 cm in length. Shing and Magur can be cultured in all types of ponds,small or big. But shallow and small ponds are well-suited for their culture.2-3 metre depth of water is good. The pond may be measures from 200 sq. metre to 4000 sq. metres. 
The bank of the pond may be vertical. It will be better if 30 cm brick made vertical wall or bamboo made fence can be erected on the bank of the pond.The pond for Shing and Magur is to be prepared in the same way as done in case of carp fish. 
The fries of Shing and Magur can be collected from natural sources. Fries of country Magur are also available at some government and non government farms. 
In cases of Shing and Magur culture, 200-300 fries can be released for every 40 sq metre. Small amount fertilizer is applied to their ponds, if cow-dung is applied at the rate of I kg. per 40 sq. metre after every 7 days, then good result can be achieved. In this case rice bran, mustard oil cake and fish meal can be supplied as food. Food is to be supplied every day at the rate of 3-5% of the total body weight of fish. But from the third month of culture the entrails of cows and goats can be supplied after cutting them. 
If supply of food and nursing are done regularly then in 6 months Magur can attain 130-150 gm, and a Shing 100-125 gm in weight. A harvest of Shing and Magur can be obtained in 6 months. In every harvest, production of 3-4 tons per hectare can be achieved.

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