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STOCK MANIPULATION AND MANAGEMENT



Jitendra Kumar, A.S. Kumar Naik, Mahesh, V. Nayana, P.

Department of Fisheries Resources and Management,

College of Fisheries, Karnataka Veterinary, Animal and Fisheries Sciences University, Mangalore - 575002, India

Email: jitenderanduat@gmail.com


The Stocking of spawn, fry and fingerlings is preferably done during morning or evening hours after proper acclimatization to new environment. The appropriate time for stocking of spawn in nursery ponds is when plankton biomass confirms to the maximum densities.


Stock manipulation or method of stocking

Stock manipulation is such as to avoid any abrupt change in quality and temperature between the water of the hatching tank and that of the Nursery pond, the post larvae should be kept in a suitable container having water initially from the former (hatching tank) to which the water from the nursery pond should be gradually added in stages, eventually substituting almost the entire hatchery water of the container by the water from the nursery pond. The container should then be slowly dipped and tilted in the Nursery pond so that the post larvae are free to swim out of the container into the Nursery pond. Stocking should be done late in the evening, a procedure which gives post larvae time to acclimatize themselves during the ensuing night relatively free from depredation, of enemies, should any have escaped the steps adopted to eradicate them.

Stocking in Nursery pond

Young carp hatchlings are very delicate and require very cautions handling. When 3-4 days old, they are stocked in a well prepared nursery pond .The spawn are reared in nursery pond up to fry stage for about 2-3 weeks.


Stocking in Rearing pond

Rearing of fry (about 20 mm long) to fingerling (about 100 mm long) stage is done in slightly bigger ponds of 0.1hac. Rearing of fry to fingerling stage is done in rearing ponds. Where fry are stocked @ 0.25-0.30 million/ha with a survival level of 60-80% under proper condition of pond.


Stocking in grow-out or stocking pond

After preparation, the stocking pond should be stocked with 100-150 mm long fingerlings. A pond having water depth of 2 to 3 m is usually stocked with 5000 fingerlings per ha. The stocking rate depends on the volume of the water and on the oxygen balance of the pond rather than the size of the pond.


Stocking of different culture system

Monoculture system

In this fish culture system only one species of fish is cultured in a pond or in this case fish farming in a certain water body is confined to a single species.


Poly culture or Composite Fish culture or mixed culture system

In this fish culture usually 3-6 compatible species of fish are cultured simultaneously in a pond, so that all available resources of food are utilised. There is no competition between the species and the yield is high.


The pond can be stocked in 3, 4 or 6 species combination as follows


Species

3-Species

4-Species

6-Species

Ratio

No.

Ratio

No.

Ratio

No.

Catla

4

2000

3

1500

5

750

Rohu

3

1500

3

1500

2.0

1000

Mrigal

3

1500

2

1000

1.5

750

Common Carp

_

_

2

1000

2.0

1000

Silver Carp

_

_

_

_

1.5

750

Grass carp

_

_

_

_

1.5

750


Mono-sex culture system

In this fish culture system, only one sex, either the male or the female, of a single species is cultivated in the water body. The sex having faster rate of growth is used, either males or females only of a species are cultured in a pond to obtain maximum yield from limited food supply.


Fingerling stocking

A combination of six species such as Indian major carps (Catla, Rohu, Nain) and exotic carps (Grass carp, Silver carp, Common carp) fulfil the criteria of species selection and prove to be an ideal combination for freshwater carp culture in India.


Stocking rate

Stocking rate of the fish depends on the fertility condition of the pond. In Indian conditions generally ponds are recommended to stock @ 5000-6000 fingerlings per ha. If stocking will be done to more than this number growth will not be satisfactory.


Post stocking management of ponds


For profitable fish culture it is necessary that the pond be scientifically managed to obtain maximum fish production. Post stocking management involves harnessing the pond productivity in the form of natural fish food, maintenance of fish pond environment favourable to the cultivated fishes and health care.



Feeding

Plankton is the best natural food for fishes. They are naturally present in ponds and used as fish food. Fish fry feed voraciously on zooplankton available in the pond, but natural food is not adequate for proper growth of cultured fishes. Artificial feed should be such that it is acceptable to fishes, easily available, cheap and easily digestible. Fish feed should have good nutritive value and high food conversion rate. Rice bran, mustered oil cake/groundnut oil cake (1:1 by weight) is considered to be cheap and best food for most of the fishes. Artificial feed is given daily @2-3% of total fish biomass in stocking pond. Feed applied in the pond in morning or evening or both times in two doses per day. Feeding place should not change suddenly. If Grass carp cultured along with major carps it is necessary to feed its preferred aquatic vegetation or green fodder such as Lemna, Azolla, Wolffia, Spirodella, Hydrilla, Ceratophyllum, Vllisneria, Nazas, Chara, Barseem leaves of vegetable etc. Grass carp require 40-50% grass of their body weight on a daily basis. The supplementary feed mixed with enough water to make dough and then applied into the pond by tray method. A better result can be obtained if feed is pelletized and sinking in nature. The feeding tray should be cleaned daily before application of fresh feed. Fortnightly or monthly, check the feeding rate and adjust accordingly. Supplementary feed should contain an adequate amount of vitamins and minerals. Fish normally stop feeding if they are sick or temperature is above or below their normal tolerance limit.


Periodic Fertilization

The desired total quantity of fertilizer is best applied in small equal doses at periodic installments throughout the rearing period so as to ensure maximum utilization of these fertilizers. The mode, sequence & timing of application of fertilizers is important to achieving the best result. Lime should be applied first then organic manure & finally inorganic fertilizers. The same order is followed subsequently. These fertilizers applied only when physical conditions of water are most suitable such as plenty of sunlight, adequate oxygen optimum temperature, adequate water level and low wind velocity. Fertilizers should be sprayed or distributed properly over the water surface during daytime when the top layer of water is warmer and lighter. Inorganic fertilizers should be stopped temporarily when nitrate and phosphate content of water show a level of 0.5ppm or above. Organic fertilizers also stopped if soil organic carbon level goes beyond 2%. When organic manure is applied in daily doses then it is more effective.


Periodical fertilization schedule


Pond type

Manure

Periodicity

Nursery

Organic

3 weeks

Rearing

Organic, inorganic

3 weeks, Daily

Stocking

Organic, inorganic

Monthly


Liming

Application of lime is first step of management for all stages of fish culture. Lime is applied in the pond on the basis of pH. Limestone is generally used in the fish pond. This is cheap and best application of lime @ 200kg/ha. In stocking pond it is used to neutralized acidity of pond water.


Role of lime in fish culture pond

  • Raise pH of water and soil.

  • Stimulate microbial decomposition of organic matter.

  • Supply Calcium to pond for fish.

  • Maintain sanitation in pond environment.

  • Kill harmful insects and their larvae.

  • Lime has anti parasitic property.

  • Destroy unwanted algae and aquatic weed for a short period of time.

  • In presence of lime NH4 compounds are nitrified into NO3 and NO2.


Pond environmental monitoring

It is important to regulate physico-chemical parameters of pond ecosystem within safe tolerance limit of cultured fish species. This is necessary periodical monitoring of pond parameter and taking corrective measures if any imbalance. Most pond parameters can be easily measured at the pond site while some require laboratory facilities.


1-Water colour

The visual colour of pond water is simple but important reflection of basic production process. Pond water colour most desirable is greenish brown.

The reddish colour of pond water is due to suspended inorganic particles. Organisms also account for red water colour examples are Purple sulphur Bacteria, Oscillatoria, Euglena sanguinaetc.

Bright green colour of pond water due to Blue green algae and Euglena.

Dark yellow colour of pond water due to Dinoflagellates (Ceratium).


2-Transparency

Transparency is synonymously used to turbidity of pond water. Pond water is said to be turbid when it contains suspended particles of silt, clay, plankton, etc. It affects pond productivity and fish life. Higher turbidity decreases penetration of light, reduces primary production and subsequently other trophic level of productivity. Optimum level of turbidity in pond should be 25-70cm. Turbidity may cause the following factors.

  • Inhibit light penetration.

  • Oxygen deficiency.

  • Reduction in primary production.

  • Gills of fish may be injured.


Control

1-Filter alum is most effective apply @25-30mg/lit.

2-Hydrated lime and Gypsum may also used.

3-Turbidity is measured by a simple instrument called Secchi Disk.


3-Temperature

Water temperature basically depends upon climatic conditions. Temperature is greatly influencing factor to fish in various ways like

1-Animal's/Fish's various metabolic activity like feeding, respiration and breeding are influenced by temperature.

2-Low temperature reduces all above activities.

3-Rise in water temperature decreases dissolve oxygen content in water.
4-Optimum temperature for better growth of IMC is ranges from 28
0c-300


4-Light

Light penetration in water depends upon several factors like intensity of light and turbidity. Light is very important factor to enhancing primary production. Phytoplankton makes their food in presence of light by photosynthesis reaction. Total light duration falling on pond as well as its biota is called photoperiod. Photoperiod largely appears to control gonadal maturity and hormonal output via hypothalamic releasing factors and finally hypothesis which release gonadotropin hormones.


5-Dissolved oxygen

Dissolved oxygen is most critical water quality variable in fish culture, so fish culturist should be familiar with the dynamic of dissolved oxygen concentrations in fish ponds. Dissolved oxygen has primary importance as regulator of metabolic process of plants and animals. Dissolved oxygen is used in respiration by animals and plants. Depletion of oxygen causes asphyxia in fishes.


Source of oxygen in pond water

  • Atmospheric air.

  • In photosynthesis reaction by aquatic plants and phytoplankton.


Loss of dissolved oxygen in pond water

  • In respiration of flora and fauna.

  • In decomposition of organic matter by the bacteria.

  • In chemical oxidation.

  • In reduction due to other gasses as H2S, CH4, CO2 etc.


Optimum level ofdissolved oxygen in fish pond should be 4-6 ppm. Excess of dissolved oxygen may be fatal due to over metabolism due to over carbon assimilation called as gas embolism.


6-Dissolve CO

Carbon dioxide is essential for photosynthesis but its excess is harmful to fish. The source of carbon dioxide in pond water through respiration of organisms, atmospheric carbon dioxide and also from decomposition of organic matter. Loss of carbon dioxide in pond water in following processes.


  • In photosynthesis.

  • In marl formation.

  • In formation of carbonic acid.


7-pH

pH is negative logarithm of H+ion concentration. pH of pond water influences the metabolism of all organisms living in pond environment. It also affects the sevsral physiological activity of aquatic animals. pH scale is ranges from o-14. pH 7 is neutral, acidic or basic pH is below or more than 7. Optimum pH for fish culture is ranges from 7.5-8.5. Acidic water reduces growth of fishes, favours infection from bacteria and other parasites.




Maintenance of pH

pH

Dose of lime (CaCO3) in kg/ha.

4 - 4.5

2000

4.5 - 5.5

1000

5.5 - 6.5

500

6.5 - 7.5

200


If pH value highly alkaline it can be controled by application of organic manure or mustered oil cake @800-1200 kg/ha. Gypsum is also used to reduce alkalinity of pond water.


Fish health monitoring

In most situations cultured fishes are healthy even in continuous presence of pathogen. When environmental stress occur and balance shift in favour of disease causing organisms then occur disease in fishes, under such circumstances fish fail to adjust adequately. So adverse environmental condition immediately should be corrected to prevent fish losses. It can be measured by the following ways.

  • Daily, weekly, fortnightly or monthly observation in fish pond.

  • Sampling and examination of fish at regular intervals for health check and diagnosis of disease if any.

  • Monitoring pond water quality and sanitation.

Signs of sickness in fishes

  1. Behavioral signs

  • Slowing down or complete stoppage of feeding.

  • Loss of equilibrium swimming erratically or spirally.

  • Surfacing for gulping air.

  • Body scrapping against the floor and sides of any rough objects.

  1. Clinical signs

  • Excess mucus secretion.

  • Change in normal coloration.

  • Erosion of fins, scales skin etc.

  • Discoloration of gills.

  • Abdominal swelling.

  • Bulging of eyes.

  • Presence of cyst, spot, or patches over body and gills.

  • Appearance of haemorrhage, lesion, and grayish or brownish area over body.


  1. Laboratory examination

Sign of disease in fish is not clearly diagnose then examine in laboratory.


Management and surveillance of fish diseases

An optimum environment always helps in good growth of fishes where as a bad environment favour multiplication of pathogen which create various diseases in fishes. Primary objective of rearing fishes is to maintain healthy fish population that are optimally eating, growing and normally functioning. To minimizing stress of fish in culture environment by understanding and managing the various environmental factors that caused stress.


Water source

The source of water is rain water, rivers, irrigation canal and ground water. Irrigation water is not always ideal for fish culture; there are chances of harbouring pathogen before entering into pond. In river water also possibility of it being loaded with sewage as well as pathogens. Thus water should be first channeled into storage cum filter tank where treatment can be done for settling of organic load killing of pathogen.


Disinfection of water

It is very essential to disinfect the water mass to make it free from pathogens. Mahua oil cake @250mg/lit is first applied then liming, it kills wild fish species, molluscs, tadpoles, frogs, parasites, insects etc. Some easily available and most effective disinfectants used to treat water.

  • Bleaching powder @ 2ppm.

  • Chlorine @5-10ppm.

  • KMnO4 @3-4ppm.

  • NaCl @1-2%.

All the fishing appliances viz. net, bucket, hapa and other things used on fish form should also is disinfected properly.


Stocking of fishes

Stocking beyond an optimum level exert pressure on the food, space, oxygen availability in the habitat thereby creating stress to fishes. Overcrowding of fish may result in easily transmission of infectious diseases. So avoid overcrowding of fish in pond.


Adequate food

Optimum amount of feed of good quality having protein, vitamins and minerals etc. should be given to fish population.


Prevent entry of wild fishes and other organisms

Wild fishes and animals often carrier of various parasites and pathogen which may cause of disease outbreaks. Dead and apparently sick fishes should be removed from the pond to prevent further infestation.


Immunoprophylaxis

It is one of the most important ways of preventing communicable diseases in fishes. In fishes internally mucus lining of gut along with enzymes serves as important defence against pathogen. There are many vaccines available in the market. Based on number of serotype of pathogen from which vaccines are prepared, one can have monovalent, bivalent, trivalent and polyvalent vaccines. This can stimulate immunity against one, two, three or several type of pathogens. Example of polyvalent vaccine is "VIBRICHTHYN" was manufactured in Germany.


Use of Probiotics

Probiotics are few good/useful microbes to compete with harmful ones and suppressing their growth. These include bacteria and yeast that promote life of host. Probiotics used in aquaculture are-

  • Lactobacillus spp. (LAB bacteria).

  • Propionibacterium spp.

  • Enterococcus spp.

  • Bifidobacterium spp.

  • Sacchromyces spp.

  • Carnobacterium divergens.


Use of Antibiotics

Antibiotics are prepared from number of bacteria fungus (Actinomyces). Antibiotics are substances produced by microorganisms which in low concentration are antagonistic to growth of other microorganisms without harming host.

Some common antibiotics used in aquaculture -

  • Streptomycin

  • Chloromycetin

  • Terramycin

  • Aureomycin

  • Neomycin


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