MANAGEMENT OF COMMON HAZARDS IN CULTURE POND

Jitendra Kumar¹*, Neeraj Pathak², Ramesh Kumar Tripathi³, Saurabh Dubey¹, Archit Shukla⁴, Mohit Kumar Ram¹, Milind Katare Mehkar¹

¹ College of Fisheries, Mangalore, ² College of Fisheries, Veraval, ³Central Institute of Fisheries Education, Mumbai, ⁴ College of Fisheries, Ludhiana, Punjab

*Corresponding author: jitenderanduat@gmail.com

Successful management of any farming system should anticipate several incidental hazards and keep ready remedial measures to deal with the situation. Based on the available data the commonly occurring serious hazards are discussed and remedial measures suggested.

Deficiency of dissolved oxygen

The most common and serious hazard in fish culture ponds is the depletion of dissolved oxygen level in the water. Gulping for air, especially during the early morning hours, is the most common behavioural symptom. The growth rate is seriously affected and very often it may result in a mass fish kill. Depending on the situation and availability of resources all such steps should be taken promptly which may help raise the DO level of the pond. The following steps are recommended:

• Add freshwater in the pond by pumping it from nearby sources. To avoid entry of undesirable fish, use a screen around the mouth of the intake pipe.

• Agitate the pond water by splashing, beating with bamboo poles, repumping with the help of a pump or using a mechanical churner/aerator.

• Apply potassium permanganate at the rate of 2—3 ppm.

• Lime at the rate of 200 kg/ha and rake up the bottom.

• Cut all the trees/branches shading the pond.

• Stop feeding and fertilization till normality is restored.

Appearance of algal blooms

Algal blooms of Microcystis sp., Euqlena sp., etc., frequently occur causing serious problems again in terms of dissolved oxygen. It creates situations where supersaturation of oxygen occurs during day time and serious DO depletion takes place during the night, sometimes leading to a mass fish kill. The following remedial measures are recommended:

• Apply chemical algicide Diuron simazine (Tafazine) at the rate of 3—5 ppm. However, mass killing and decay of algae may also cause DO depletion.

• In small ponds cover part of the pond with duck weeds or other floating

  weed like Pistia to reduce the amount of sunlight entering the pond. This will result in the death of algal cells. Gradually cover the whole pond, part by part.

• Add fresh water if possible from nearby sources, taking care to prevent entry of unwanted fish.

• Stop feeding and fertilization till normality is restored.

Problem of no rain and plenty of rain

During drought the water level drops down to critical levels in some ponds, while during seasons of heavy rains the incidence of flooding is not uncommon.

• Keep constant vigil on water level. Before it drops below the 1.25 m mark, water should be added from nearby sources. Keep alternative source of water ready for such occasions. A shallow tube well could be of some help to fight against drought.

• Harvest the fish before such a situation is encountered.

• Repair and strengthen the dykes before the onset of rains. Entry point and spillway should be properly guarded by strong fine meshed steel netting.

• Harvest the fish before the flood season if cost of protection becomes too high.

Problem of predation

By far the most important and damaging predators of fish in ponds are otters, snakes, frogs, birds, etc. Otters can be prevented by putting a fence around the pond. Snakes, frogs and birds cause problems mostly in nursery and rearing ponds. Ponds in the vicinity of the fish farmer's home are less likely to be affected by these predators than the ponds that are isolated and seldom visited. Frogs normally lay eggs in shallow pits along the sides of seasonal nursery and rearing ponds during the first monsoon shower. All such spots should be identified and the eggs should be destroyed. Bird-scaring devices, including fire crackers should also be used if the problem becomes severe.

Poaching

Poaching is perhaps the biggest problem in freshwater aquaculture. High value and ready market for carps make them more prone to poaching. The widely used gears for poaching are cast nets, gill nets and small drag nets. The following measures have been found to be most effective against such forms of poaching:

• Place branches of trees and bamboo twigs in the grow-out pond along the sides. Nursery and rearing ponds are usually not prone to poaching.

• Stretch and fix barbed wire in criss-cross manner in the pond, especially along the sides.

• In large ponds, occasionally row a boat with hooks or barbed wire hanging from its keel to detect gill nets.

• Fencing the farm with barbed wire and employing the services of watchmen are efficient means of preventing poaching.

• Trained dogs used for night watch minimizes the risk considerably.

Leakages in embankment

Sometimes leakages do occur in embankments and if not checked immediately they could cause extensive damage to the pond embankment. If the leaking water is clear and flow velocity is sluggish it may be seepage water and hence there may not be any immediate danger. In case the water flow is fast and muddy, immediate steps must be taken to locate the hole on both sides of the embankment. Muddy water shows soil erosion and washing away of soil particles. To locate the hole, heavy turf sod should be thrown on the water surface which gets attracted towards the hole and the sod may come out of the pond through the hole. Whirling action of water may be noticed just above the leak if it is big.

Leakages can be checked by pushing sawdust, bran, etc., into the upstream site. These are carried by water into the leak where it swells and stops the leak. In case of major breaches which may occur and cause severe damage to the embankment, sufficient material and labour resources must be mobilised. The outside of the banks should be protected first to prevent further erosion. A semicircular bundh may be constructed on the inside with brushwood, bamboo nettings and sand bags to facilitate repairing the breached portions with earth and sand bags.

Outbreak of diseases

General considerations

The fish farming system in general is unique in that the cultured animal is cold-blooded or poikilothermic and lives in water, where the respiratory oxygen level is limited and may become lethal at times. Also, metabolic waste products, left-out feed materials and organic load of the pond bottom regularly come into contact with certain vital organs and tissues. In an undrainable pond system no addition of water or aeration is normally done and the accumulated wastes are not usually removed unless provision is made to desilt the pond after a couple of years. All such factors can cause deterioration of fish health and magnify the risk of outbreaks of diseases.

There are two strategies for the management of this hazard, viz. prevention of disease through prophylactic measures and treatment and control of disease outbreaks using fish therapeutics. There is a common saying that an ounce of prevention is worth a pound of cure. This saying has great value in fish health management. Preventive measures have always big advantage over curative practices. If you prevent the disease outbreak you have virtually no loss, but if you want to cure the outbreak you will always have some losses before you treat and cure them. Moreover, the drug may not provide remedies under all circumstances. Also, the drug may not help the host survive the infection until the environment is improved. Ideally, the aquaculturists should strive to decrease the stress causing factors, eliminate and prevent the entry of pathogenic organisms, etc., by strictly adhering to the fish health monitoring programme.