This article throws light upon the top three managements of composite fish culture. The managements are: 1. Pre-Stocking Management 2. On Stocking Management 3. Post-Stocking.
Composite Fish Culture: Management # 1.
(i) Construction of a Fish Farm:
(a) Site Selection:
The availability of cheap land and plenty of unpolluted freshwater.
1. Water quality:
Biological and physicochemical nature of water and their seasonal variations.
There should be replacement and recycling facility.
3. Soil quality:
A selected site’s soil in its every 100 gm. should contain 50- 75 mg nitrogen, 6-12 mg phosphorous and 1.5- 2.5 gm. organic carbon. For good production from cultured fish soil pH should be in between 7.5- 8.5.
4. Fish seed:
Availability of quality fish and prawn seed of required species with the transportation facilities to the site and assurance of supply in required time.
5. Fish feed:
The 60% of the expenses of total operational cost of fish farming goes for feed alone. They need to be fed with grass like- para, Napier, maize leaves, banana leaves, chopped green cattle fodder, etc.
6. Climatic factors:
Rainfall, temperature, evaporation rate, flood, cyclones, etc. are the important climatic factors. The growth of fish depends upon these factors. Sometimes flood, drought, etc. cause heavy loss to the fish farmers.
7. Industrial and agricultural pollution:
The insecticides used in agriculture are toxic to fish. Beyond a certain level, heavy metals and various chemicals discarded from industries are also poisonous to fish.
8. Infrastructural facilities:
For establishing a new farm various infrastructural facilities are required and they are- communication facility,- electricity supply, cold storage facility, nearness to market, support from Government and local authorities, support of universities, research centres, extension centres, etc.
9. Construction expenses:
The expenses for earth moving, RCC work, workshop, repair and spare parts, cost of construction materials, like-brick, rubble, steel, cement, etc. need to be surveyed. The major item of construction expenses goes for earth moving and RCC work. Earth moving can be done either manually or mechanically depending on the cost of labour.
10. Availability of labour:
Skilled, unskilled, casual and construction labours are required for establishing a farm.
11. Financial facilities:
Capital for the scheme can be raised either by loan from commercial banks or from equity participation. Availability of such facilities at a particular area should be studied well in advance. Availability of subsidies and other financial assistance from Government or other developmental organization for the proposed area also should be taken care of.
12. Marketing facilities:
The farmed product can be sold either to internal market or to export market. In both cases the taste of consumer and the provision for supplying the product to the consumer should be observed.
13. Availability of equipment’s and other inputs:
The equipment’s require for fish farming practices should be available at the site or they can be procured from a nearby place having transportation facilities at reasonable price.
(b) Pond Construction:
Scientifically constructed fish farm has 3 types of ponds:
1. Nursery pond:
Area of nursery pond ranges from 100- 500 m2 and the depth of water should be in between 1-1.5 m. This pond covers 5 % area of total productive area of the fish farm.
2. Rearing pond:
Area of rearing pond varies between 500-1000 m2 and the depth of water ranges from 1.5- 2.0 m. This type of pond covers 15 % area of the total productive area of the fish farm. Sometimes it may be used as stocking pond also.
3. Stocking pond:
Area of stocking pond varies between 1000- 20000 m2 and the depth of water ranges from 2- 2.5 m. This type of pond covers 60- 70 % area of the total productive area of the fish farm.
The above mentioned pond of a fish farm is constructed in 2 ways:
1. Dug out pond:
This is constructed in a plain area by digging soil. This type of fish pond is more suitable for fish farming as they can be constructed by the fish farmer based on their requirements scientifically by maintaining the shape, size, depth, etc. Normally small size rectangular pond is preferred. But pond may be of any shape like- circular, square, rectangular, etc.
2. Embankment Pond:
This type of pond is constructed in undulating and hilly areas. This is constructed by erecting dyke on 2 sides or in 1 side of he selected place on need basis. This is economic to dig out pond from me construction side, but it is not good from the fish culture point of view. Thus is because the size, shape, depth, etc. can not be fixed as per the scientific fish culture specification, which are depended upon the site configuration.
Normally this type of pond is constructed in hilly places by erecting embankments to a suitable height for fish culture with provisions of inlet and outlet. Here in the inlets and outlets small mess size bamboo made or nylon made screen is tied. This prevents the entry of unwanted fish, aquatic insects, etc. into the culture system and also stops the escaping of cultured fishes from the culture system.
Based on the aim and the facility available with a fish farmer the aforesaid ponds are dug out on scientific basis. During digging of a pond along the side slope should maintained so that it is not eroded. This side slope depends upon the soil quality. For loamy or clay loam soil the side slope should be 1.5:1.
If the selected site contains more sand than this side slope should be little more. Constructed fish pond should have a slope towards a particular side or towards the centre, then dewatering become easier.
Construction of embankment:
Fish pond embankment should be strong enough and their height should be 1 ft. more than the high flood level of the selected site.
The bases of the embankments are constructed based on the height and slope required for it. Embankments width at the top and its side slope depends upon its height, nature (Peripheral dyke or internal dyke), purpose of use (for walking, for movement of small car, for movement of big vehicle, etc.), etc.
Generally in case of clay loam or loamy soil the pond dyke’s external side slope should be 1:1.5 and for internal side’s the side slope should be 1:2. Sandy soil is not good for construction of embankment as in this case the erosion will be more.
Outlet and inlet maybe constructed in the pond embankments at the desired height to maintain the water level in the pond at the required height, but in that case to prevent the entry of unwanted fish, insects & other organisms and also to prevent the escape of cultured fishes there should be some arrangement like- erection of net of bamboo made or nylon made.
To prevent the soil erosion of pond embankments grasses should be grown over them.
Fencing is essential along the boundary of fish farm to prevent the entry of domestic animals, like- cow, goat, etc. From time to time embankments should be checked for any damage and repairing should be done. This helps in lasting the embankment for prolong period.
(c) Pond Preparation for Stocking with Fish
1. Liming and Fertilization:
Lime is anti-parasitic, destroying, parasites living in the water or in the intermediate hosts. Lime is generally used and is spread on the pond bottom for 10- 15 days before stocking the pond with fish. Lime is used in different forms such as lime stone, quick lime, calcium cynamide, caustic lime etc.
After 7-10 days of liming fertilization pond water is done. Cow dung @ 670 Kg/ ha/year is applied as organic fertilizer. Inorganic fertilizer- urea @ 13 kg/ha/year, SSP @ 3 Kg/ha/year and muriatic of potash @ 12 kg/ ha/year is applied after 7- 15 days of application organic fertilizer.
1 /3 of the required amount of lime and fertilizer is applied initially to the pond, and then the rest amounts is divided equally into 11 installments and are applied to the pond at monthly regular interval. Then by seeing the pond productivity after 7-15 days of application of inorganic fertilizer fish seed is released to the pond water.
Composite Fish Culture: Management # 2.
On Stocking Management:
(i) Selection of Species:
(a) Species Selection Criteria:
Fish species selected for culture should have the following characters-
1. Fast growth rate.
2. Good food conversion efficiency.
3. Acceptability of supplementary and natural food.
4. Adaptability to crowded conditions and resistance to diseases.
5. Ability to withstand changing physico-chemical and biological conditions of the pond water.
6. Good market value.
Rohu (Labeo rohita), Catla (Catla catla), Mrigal (Cirrhinus mrigala) Silver carp (Hyvovhthalmichthys molitrix), Common carp (Cyprinus carpio) Grass carp (Ctenovharyngodon idella), Tilapia (Oreochromis mossambica), Magur (Clarias batrachus), Java puthi (Puntius javanicus) Kurhi (Labeogomus), Fresh water prawn, etc.
(ii) Size, Quality, Number and Composition of Fish Species to be stocked:
(a) Size of Fish Seed to be stocked:
Considering the environmental condition which allow only a short period for growing of fish, stocking of pond with yearling is always best to get a good Fish fingerling i.e. 10-15 cm size fish seed is the best stocking material in the stocking pond.
(b) Quality offish Seed to be stocked:
Farmers should collect the fish seed from a known source who is maintaining a good quality stock of brood fish for production of fish seed.
(c) Number offish Seed to be stocked:
In composite fish culture in stacking pond, fish seed of 10- 15 cm length (fingerling) is stocked at the rate of 7000-8000 nos. / Ha. (900-1000 nos. /ha).
(d) Percentage offish Species Composition (numbers/ha)
Composite Fish Culture: Management # 3.
(i) Water Quality:
Different kinds of substrates have different effects on the water quality in the pond. For example, bamboo is more resistant and requires less dissolved oxygen than easily degradable organic substrates, such as Fish farming ponds 33 sugarcane bagasse or paddy straw.
Also, depending on the position of the substrate in the water column, periphyton mats are either oxygen producers (upper water layer) or consumers (bottom water layer). By controlling the distribution of substrates in the water column, one can help to prevent oxygen shortages in the pond.
The periphyton mat entraps suspended solids, which improves water transparency and thus the penetration of sunlight into the pond. The periphyton mat also takes up compounds that are toxic for the fish, like ammonia and nitrate.
Ammorua toxicity is an important constraint in the intensification of fish farming in pond systems. In periphyton- based ponds, bacteria that break down ammonia can colonies the surface of the substrates located in the well-oxygenated water column. These mats form a ‘bio-filter’ that keeps ammonia levels low.
(a) Water Temperature:
Water temperature is an important condition in assessing whether the fish species selected can be raised. A water temperature between 20-30°C is generally good for fish farming.
Oxygen is a gas that is produced by all plants in the pond (therefore also by phytoplankton) with the help of sunlight. The more sunlight falls on the pond and the larger the quantity of phytoplankton, the higher the oxygen-production will be. The oxygen produced partly dissolves in the water and the rest escapes to the air.
The oxygen level of the water varies during a 24-hour period because the production and absorption of oxygen by the plants change with light and darkness.
The phytoplankton’s in the pond only produce oxygen when there is light. At night they need oxygen like any other plant or animal in the pond, but because of the lack of sunlight no oxygen can be produced. Consequently, the quantity of dissolved oxygen in the water decreases after sunset.
Normally, the oxygen level is at the highest at the end of the afternoon (oxygen has been produced throughout the day) and at the lowest in the early morning (oxygen has been used up throughout the night). Shortage of oxygen is the most important cause of fish death when the pond has been fertilised with manure or fed too much.
A sufficiently high oxygen level is important for good fish production. If fish are gulping for oxygen at the water surface, you can solve this problem by flowing extra freshwater through the pond. Stirring up the water in the pond also helps to increase the amount of dissolved oxygen.
Do not feed and fertilize the pond at this moment because this is often one of the reasons for the oxygen shortage. Over- stocking of fish in the pond could be another possible cause of oxygen shortage problems. This can cause oxygen stress for the fish, which can result in disease outbreaks and mortality.
(c) Water Acidity, Alkalinity and Hardness:
Water suitable for fish farming should have a certain degree of acidity, indicated by the water pH-value. This should preferably range between 6.7 and 8.6 Values above or below this range inhibit good fish growth and reproduction. Phytoplankton require a pH of about 7 and zooplankton (tiny animals in the pond water on which the fish feed) a slightly lower pH of 6.5. Sometimes the pH of the pond water can change quickly.
For example, heavy rain may carry acid substances, dissolved from the soil into runoff water, into the pond. In this way, the pond water gets more acid and thus the pH-value decreases.
The best way to increase the pH-value of the water again to neutral (about 7) is to add lime to the pond. Water alkalinity is a measure of the acid-binding capacity of the water (buffering ability), and is the opposite of water acidity. This means that when pond water alkalinity is high, more acid substances are needed to decrease the water pH-value. Water hardness is the measure of total water-soluble salts.
Water that contains many salts is called ‘hard’ and water that contains few salts is called soft. One method of measuring hardness is to carefully examine the pond dikes. If a white line appears on the dike at the same height of the water level, this means that salts present in the water have dried on the pond dikes.
Therefore the pond contains hard water. Hard water is important for good fish growth. If the water is too soft (i.e. the amount of water soluble salts is low), the farmer can increase the water.
Turbidity is the term for the amount of dissolved, suspended dirt and other particles in the water, which give the water a brown colour. High turbidity of water can decrease fish productivity, as it will reduce light penetration into the water and thus oxygen production by the water plants.
Dissolved, suspended solids will also clog filters and injure fish gills. A method for measuring water transparency, and therefore an indirect way to estimate turbidity, is the Secchi disc.
Methods for Reducing Turbidity:
1. Use of a silt catchment basin:
This is a small reservoir at the inlet of the pond. The water flows into this reservoir and is kept there until the mud settles on the bottom. Then the clear water is let into the fish pond. Another way of clearing muddy water is to place hay and/or manure in the pond and leave it there to decompose (resulting in sedimentation of mud particles).
This method should not be used during very hot weather because the hay will begin to rot very quickly. This could lead to oxygen shortage in the pond. In the case of water turbidity caused mainly by factors other than phytoplankton abundance (water colour is not greenish), there are some widely used practices to decrease this turbidity.
For instance, before stocking the fish, place animal manure in the pond at a rate of 240 g/m2 Do this three times with an interval of three to four days between the applications.
2. Application of lime and gypsum:
Application of lime, gypsum, or preferably alum at 1 gram per 100 litres of water reduces the turbidity.
(e) Toxic Substances:
Toxic substances in the water supply of the pond can decrease fish production seriously, so it is wise to investigate any existing or potential sources of water pollution in the vicinity of the pond. Many chemicals used in animal husbandry and crop cultivation are poisonous to fish. Therefore, chemicals should never be used in the area around the pond, especially avoid spraying on windy days.
1. Fish Health Management:
Cultured fish should check regularly for their health. If any deviation in their normal behaviour is seen then they should be treated with the advice of an expert.
2. Harvesting Management:
After 7- 8 months of growing cultured fishes reaches marketable size. The grass carp and silver carp becomes 1 kg size in 7- 8 months cultured period. To reach 750 gm. to 1 kg rohu, catla, mrigal, etc. needs about 1 year growing period. When the cultured fish reaches 750 gm. to 1 kg. In weight then they are harvested from the pond.
The harvesting may be done by removing the complete stocks of cultured fishes or by removing the only table size (750 gm. to 1 kg) fishes partially based on market demand. In case of partial harvesting the numbers of fish harvested from a pond is replenished with equal numbers of small fishes from nursery ponds of the farm. This helps in getting more money.