How to overcome the problems faced by fish culture???
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Composite fish farming runs the risk of encountering several incidental hazards, which may cause heavy losses unless they are anticipated and remedial measures taken in time in order to overcome them.
Most of the problems emanate because of poor management.
Hazards may be either biological or problems of management or harvesting.
Biological Problems:
Biological hazards arise from the existence of weeds, predatory fishes, insects and snakes in the culture ponds.
These problems can be controlled if sufficient measures are taken before stocking fishes in between successive cultures.
Aquatic weeds, if any found in the pond can be very effectively controlled by the introduction of weed eating fishes like grass carp and Puntius species.
These should be eradicated during the preparation of the pond.
Aquatic insects such as beetles: Cybister, Stemolopus; bugs: Belostoma, Anisops and dragon fly nymphs, etc. should be eradicated.
Others like snakes also cause considerable damage to the fish crops by feeding on fingerlings.
Molluscs in large numbers always affect the fish adversely. They can be controlled by stocking the fish.
Due to the early maturity and natural breeding of the common carp, the rate of these fishes is increased and the stocking density of the culture pond is greatly altered unless some precautionary measures are taken.
Hence, common carp may be harvested before they are fully ripe. Otherwise aquatic weeds can be kept in the corners of the pond to lay eggs which are adhesive in nature.
The weeds with attached eggs can be removed and the eggs, if so desired, can be incubated separately to obtain hatchlings. By this, the farmers will avoid the breeding of common carp in the pond with less cost and at the same time raise the spwan for sale.
Common carp, because of its burrowing nature, it can spoil the dyke by making holes in it.
Crabs also damage the dyke. Tilapia is a continuous breeder; hence it must be avoided in the ponds.
Algal blooms with Microcystis, Euglena, etc. which are found generally in summer months cause serious problems of dissolved oxygen.
During day time, oxygen is supersaturated and in the night oxygen is depleted.
The chemical method is good for eradication of blooms. Pumping of freshwater into the pond at the time of emergency is a safe method.
Addition of KMnO4 (1 ppm) increases the dissolved oxygen content of water and also acts as a disinfectant.
Quick-lime or slake-lime at a rate of 200 Kg / ha should also be added to counteract the adverse effect of putrification of organic matter.
Repeated drag net operation in the pond facilitates the release of obnoxious gases. Cut banana stem has also beneficial effects on the fish in the above circumstances.
In composite fish culture, excessive growth of plant material is cut down by silver carp and grass carp which subsist on phytoplankton and aquatic weeds respectively.
Presence of mrigal and common carp also considerably reduces the adverse effects created by the depletion of oxygen due to the decomposing organic matter since they feed on it.
The situation becomes much more serious during windy days and especially during spring when the falling leaves start putrefying in the water.
Banana plantation should not be allowed to become bushy. The dwarf variety is most suitable for this purpose.
Management problems
It is always necessary to maintain at least 2 m of water depth in the pond.
Serious drought severely affects the level of the water in the rain-fed ponds. Alternative sources of water supply like tube-wells could be of helps in fighting against the drought.
Heavy rain and flood cause serious damage to the ponds by breaking the dykes or over flooding them. In both the cases, the fish escape from the pond.
Temporary measures such as protection of the dykes or screening of the ponds may be resorted to. Sometimes, it is better to harvest the fish.
Trained watch-dogs may prove more effective and economical in controlling poaching.
Harvesting Problems
It is essential to harvest the fish stock before the growth rate of the fish for the invested inputs such as feed and fertilizers start declining.
The nutritive value of water for feeding the fish cannot be increased after a certain stage.
.
The sale prices of fish of less than a Kg is somewhat less as compared to those fish which weighs over a Kg or so. This also influences the harvesting programming and to get more profit, it is essential to consider this aspect also before harvesting.
Inter-relationship of the species cultured is also required to be seriously considered. Bottom feeders subsist partly on faecal matter of grass carp and an unplanned removal of grass carp would, in turn, affect the growth of the bottom feeder whereas if only bottom feeders are totally harvested the excessive faecal matter of grass carp may pollute the water.
The hazards involved in composite fish culture are manageable and could be effectively averted by proper precaution and vigil.
Most of the problems emanate because of poor management.
Hazards may be either biological or problems of management or harvesting.
Biological Problems:
Biological hazards arise from the existence of weeds, predatory fishes, insects and snakes in the culture ponds.
These problems can be controlled if sufficient measures are taken before stocking fishes in between successive cultures.
Aquatic weeds, if any found in the pond can be very effectively controlled by the introduction of weed eating fishes like grass carp and Puntius species.
These should be eradicated during the preparation of the pond.
Aquatic insects such as beetles: Cybister, Stemolopus; bugs: Belostoma, Anisops and dragon fly nymphs, etc. should be eradicated.
Others like snakes also cause considerable damage to the fish crops by feeding on fingerlings.
Molluscs in large numbers always affect the fish adversely. They can be controlled by stocking the fish.
Due to the early maturity and natural breeding of the common carp, the rate of these fishes is increased and the stocking density of the culture pond is greatly altered unless some precautionary measures are taken.
Hence, common carp may be harvested before they are fully ripe. Otherwise aquatic weeds can be kept in the corners of the pond to lay eggs which are adhesive in nature.
The weeds with attached eggs can be removed and the eggs, if so desired, can be incubated separately to obtain hatchlings. By this, the farmers will avoid the breeding of common carp in the pond with less cost and at the same time raise the spwan for sale.
Common carp, because of its burrowing nature, it can spoil the dyke by making holes in it.
Crabs also damage the dyke. Tilapia is a continuous breeder; hence it must be avoided in the ponds.
Algal blooms with Microcystis, Euglena, etc. which are found generally in summer months cause serious problems of dissolved oxygen.
During day time, oxygen is supersaturated and in the night oxygen is depleted.
The chemical method is good for eradication of blooms. Pumping of freshwater into the pond at the time of emergency is a safe method.
Addition of KMnO4 (1 ppm) increases the dissolved oxygen content of water and also acts as a disinfectant.
Quick-lime or slake-lime at a rate of 200 Kg / ha should also be added to counteract the adverse effect of putrification of organic matter.
Repeated drag net operation in the pond facilitates the release of obnoxious gases. Cut banana stem has also beneficial effects on the fish in the above circumstances.
In composite fish culture, excessive growth of plant material is cut down by silver carp and grass carp which subsist on phytoplankton and aquatic weeds respectively.
Presence of mrigal and common carp also considerably reduces the adverse effects created by the depletion of oxygen due to the decomposing organic matter since they feed on it.
The situation becomes much more serious during windy days and especially during spring when the falling leaves start putrefying in the water.
Banana plantation should not be allowed to become bushy. The dwarf variety is most suitable for this purpose.
Management problems
It is always necessary to maintain at least 2 m of water depth in the pond.
Serious drought severely affects the level of the water in the rain-fed ponds. Alternative sources of water supply like tube-wells could be of helps in fighting against the drought.
Heavy rain and flood cause serious damage to the ponds by breaking the dykes or over flooding them. In both the cases, the fish escape from the pond.
Temporary measures such as protection of the dykes or screening of the ponds may be resorted to. Sometimes, it is better to harvest the fish.
Trained watch-dogs may prove more effective and economical in controlling poaching.
Harvesting Problems
It is essential to harvest the fish stock before the growth rate of the fish for the invested inputs such as feed and fertilizers start declining.
The nutritive value of water for feeding the fish cannot be increased after a certain stage.
.
The sale prices of fish of less than a Kg is somewhat less as compared to those fish which weighs over a Kg or so. This also influences the harvesting programming and to get more profit, it is essential to consider this aspect also before harvesting.
Inter-relationship of the species cultured is also required to be seriously considered. Bottom feeders subsist partly on faecal matter of grass carp and an unplanned removal of grass carp would, in turn, affect the growth of the bottom feeder whereas if only bottom feeders are totally harvested the excessive faecal matter of grass carp may pollute the water.
The hazards involved in composite fish culture are manageable and could be effectively averted by proper precaution and vigil.
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