Fish Farming Guide: Water Parameters and Pre-Stocking

Fish farming is influenced by various factors that affect the production and overall success of fish culture. This article explores the importance of water temperature, alkalinity, dissolved oxygen, ammonia, and turbidity in fish farming. Understanding and managing these factors is crucial for maintaining optimal conditions for fish growth and maximizing productivity.

 1. Water Temperature:

This plays a vital role in the production of fish food and ultimately in the production of fish.

Cold water is less productive due to its low temperature essential to supply more supplementary feed, the cost of production is high and turns beyond the reach of the people.

In warm water, with fewer efforts, natural fish food source, plants, and animal origin, water is productive. With increased fish production, the cost of the product is reduced- fishes are available to a mass of people.

Temperature above 20°C to 30°C is considered most suitable for fish culture.

2. Alkalinity of Water:

In fish culture, the most preferred pH range is 7 to 10. A pH value below 6 is not preferred as the acidic water remains unproductive. To make the pH more alkaline, the pH value of 6 is manipulated using lime. The most suitable pH range for fish culture is considered to be 7.5 to 8.5.

3. Dissolved Oxygen:

In fish culture, water quality is defined by the amount of oxygen dissolved in the water. The purity of water is determined by the presence of high levels of dissolved oxygen.

Rivers and streams naturally contain high levels of oxygen due to their aerated nature. Good water quality is considered to have a dissolved oxygen level of below 4 mg/l, with an ideal range being between 5-10 ppm.

Oxygen depletion in water is rectified by following the aeration methods;

The manual method of oxygenating water involves splashing the surface with bamboo sticks. This process helps to dissolve the oxygen in the water.

The mechanical method of oxygenating water uses a diesel water pump. The pump operates by pumping water out and spreading it into the water body, which leads to the dissolution of atmospheric oxygen.

Aerators are floating devices that have mechanical rotating blades that churn the water. This helps to dissolve the oxygen in the water and ensure that it remains well-oxygenated.

(4). Ammonia:

In general, ammonia is toxic to fish and the concentration of ammonia that is safe for fish is determined by the pH and temperature of the ionized ammonia. A safe concentration for fish is between 0.02-0.05 mg/l.

To reduce the concentration of ammonia in a fish pond, it is recommended to avoid overfeeding and excess liming. Formalin can also be used to remove ammonia from the pond.

Additionally, water exchange and aeration can also help to reduce ammonia levels. Aeration specifically increases the concentration of Dissolved Oxygen and decreases the Ph, leading to a decrease in toxicity.

5. Turbidity:

There are two types of turbidity present in the water.

a). Mineral turbidity:

If the water appears to be mineral turbid (brownish in color), it is necessary to seek assistance from a laboratory to determine the weight of suspended material in a given volume of water, known as the total suspended solids (TSS), which is typically expressed in milligrams per liter (mg/l).

While collecting samples, care must be taken to avoid disturbing the water too much as this can easily increase the TSS, and samples should not be taken solely from the surface as the water is typically less turbid in that area.

The amount of total suspended solids (TSS) in pond water determines the level of mineral turbidity. If there is less than 25 TSS (mg/l), the mineral turbidity is considered low. The mineral turbidity is medium if it falls between 25-100 TSS (mg/l).

On the other hand, if the TSS is over 100 (mg/l), the mineral turbidity is considered high.

b). Plankton turbidity:

If it is plankton turbidity (greenish water), you can estimate the level yourself using the two simple methods described below. They will also give you an estimate of the potential fertility of your pond, from which you can decide on the kind of management practice to be applied.

i). Measuring plankton turbidity with your arm

This is a very simple method that does not require any special equipment. To perform the procedure, slowly wade into the shallow part of your pond, being careful not to disturb the pond bottom too much. Once in the pond, stretch one arm and immerse it vertically into the water until your hand disappears. Take note of the water level along your arm.

If it is well below your elbow, plankton turbidity is very high. If it reaches to about your elbow. plankton turbidity is high. If it reaches well above your elbow, plankton turbidity is low.

ii). Making Secchi Disc

Procedure;

The Secchi disc is a simple tool that can be used to give a better estimate of turbidity. It is particularly useful in green-colored ponds to estimate plankton turbidity. This measurement is then called the Secchi disc transparency.

1. Cut a round disc about 2cm in diameter from a piece of wood or metal, such as a pounded tin can.
2. On its surface, mark two lines to make four quarters. Paint these black and white using matt paint to prevent glare.
3. Drill a small hole at the center of the disc. Through this hole pass a line or a piece of string about 1 to 1.5 m long.
4. Below the disc, attach to the line a small weight such as a long bolt or a stone.
5. Fix the disc at the bottom of the line, against the bottom weight, by knotting the line around a small piece of wood or metal, across the top of the disc.
6. Mark the rest of the line with knots or tightly tied colored thread at 10cm intervals.

Note: Instead of using a line, you may also attach the disc from its center to a graduated vertical stick about 100 cm long.

Measuring the Secchi disc transparency.

 Procedure;

1. Slowly lower the disc into the water.
2. Stop when it just disappears.
3.  Note at which point the line breaks the water surface. Mark this point A.
4. After noting at which point along the line the disc just disappears, lower the disc a little and then raise it until it just reappears. Mark this point B.
5. Mark point C, midway between points A and B.
6. Measure the transparency of the water as equal to the distance from the top of the disc to this point C, counting the knots along the line. This figure is the Secchi disc transparency.
7. To obtain the best measurement, take note of the following points:

Points to note to obtain the best Measurements while using Secchi disc transparency.

1. Measure transparency between 09.00 hours and 15.00 hours on calm days.
2. Whenever possible, do the readings when the sun is out, not behind a cloud.
3. Look at the sinking disc from directly above, if possible with the sun behind you.
4. Keep the disc clean, particularly the two white quadrants. If necessary, repaint the disc in black and white.

Interpreting Secchi disc transparency results;

1. Less than 40 cm: there is too much plankton and your fish are in danger during the night when oxygen is not produced by photosynthesis and when too much oxygen is consumed by the respiration of this plankton.
2. 40 to 60 cm: fish production will be the best.
3. Over 60 cm: there is too little plankton, and your fish do not have enough natural food to eat.

Pre-Stocking Management

The practices and steps are similar to that of rearing ponds. A major concern in growing out ponds is as follows;

1. Process of Eradication of Aquatic Plants and Weeds:

Weed-infested ponds can be controlled biologically by stocking grass carp, as their feeding habit focuses on aquatic plants and weeds. The feeding for grass carp should be adjusted based on their different stages of life, with fingerlings (4.0-15.0cm) and juveniles/adults (above 15.0cm) receiving different diets.

In addition to regular feeding, grass carp can be fed green animal fodder such as Napier, hybrid Napier, elephant grass, and tender leaves of vegetables and trees such as drumstick.

2. Removal of Predatory Fishes:

Fish toxicants: Although several chemicals and plant derivatives are available in the market which is poisonous for fish, only a limited number of such toxicants are safe and suitable for fish culture purposes.

Based upon the following criteria, a suitable fish poison is selected as seen below;

1. Poisoned fish should be safe for human consumption.
2. Least adverse effect on the pond biota.       
3. The toxicity period should be of short duration.
4. Should not have a residual effect.
5. Easy commercial availability.
6. The simplicity of application.
7. Cost considerations.

Application of Toxicants in Ponds

Basia latifolia oil cake, bleaching powder, and ammonia are considered suitable toxicants.

(a). Basia latifolia oil cake:

Of all the plant-origin fish poisons, the most widely used toxicant in stagnant ponds is the oil cake of Basia latifolia. It can kill all fish species within a few hours when applied at a rate of 250 parts per million (ppm).

The oil cake contains 4-6% of the active ingredient, saponia, which, upon dissolution in water, hemolyzes red blood cells and kills the fish.

To use, the required quantity of mohua oilcake should be soaked in water and then evenly distributed across the entire pond surface. After application, repeated netting should be done to ensure proper mixing of the poison and to remove affected fish that are suitable for human consumption.

The toxicity of doses up to 250 ppm lasts for about 96 hours, after which it serves as organic fertilizer in the pond. It should be applied at least two weeks before stocking the pond with fish.

(b). Bleaching powder

Bleaching powder or Calcium Hypochlorite (CaOCI2) is an effective and safe toxicant for fish. When applied at a rate of 25-30 ppm, it eliminates all predatory and weed fish in the pond.

However, during storage, there is a significant loss of chlorine content, so it is safer to use commercially available bleaching powder at a rate of 35-50 ppm or 350-500 kg/ha/m of water.

The toxicity of the bleaching powder causes a fish kill within 1-3 hours and lasts for 3-5 days. After 7-8 days, plankton and benthic fauna begin to develop again.

Bleaching powder is particularly useful in undrainable ponds, where sun drying is not an option, as its chlorine content thoroughly disinfects the water.

Disinfection is crucial for maintaining the health of fish, and it also meets the lime requirements of the pond soil.

The application process is straightforward - the powder is mixed with water and spread evenly over the water's surface. Dead fish can then be removed with a net. The chlorine-killed fish are safe for human consumption.

(c) Ammonia

Anhydrous ammonia when applied at the rate of 20-25 ppm kills the predatory and weed fishes. Besides, it also controls the aquatic weeds and later acts as nitrogenous fertilizer.

The toxicity of ammonia lasts for 4-6 weeks.

Recommended doses of fish poison.

1. Bleaching powder: 350-500 kg/ha/m
2. Mohua oil cake: 2500 kg/ha/m.
3. Anhydrous ammonia: 20-30 kg/ha/m.
4. Powdered seed of Croton tiglium: 30-50 kg/ha/m.
5. Root powder of Milletia pachycarpa: 40-50 kg/ha/m.
6. Seed powder of Milletia piecidia: 40-50 kg/ha/m.
7. Seed powder of Barrinqtonia acutanqula: 150 kg/ha/m.
8. Seed meal of tamarind (Tamarindus indica): 1750-2000 kg/ha/m.
9. Tea seed cake (Camellia sinensis): 750 kg/ha/m.

Conclusion

In conclusion, maintaining optimal water conditions is essential for successful fish farming. Factors such as water temperature, alkalinity, dissolved oxygen, ammonia levels, and turbidity directly impact fish production and overall pond health. By understanding and managing these parameters, farmers can create a favorable environment for fish growth and ensure sustainable aquaculture practices.

Controlling water temperature within the suitable range of 20°C to 30°C promotes increased fish production, making it more accessible and affordable to a larger population. Maintaining alkalinity between pH 7 to 10 supports productivity, while dissolved oxygen levels should be maintained above 4 mg/l or ideally between 5-10 ppm for good water quality.

Ammonia concentration should be carefully monitored, as high levels can be toxic to fish. Proper feeding practices, water exchange, aeration, and the use of formalin can help manage ammonia levels effectively. Additionally, turbidity, whether mineral or plankton-based, should be assessed and controlled to ensure the right balance for fish and their natural food sources.

In pre-stocking management, measures such as the eradication of aquatic plants and weeds, as well as the removal of predatory fishes, contribute to maintaining a healthy fish pond. The use of appropriate fish toxicants, such as Basia latifolia oil cake, bleaching powder, and ammonia, can help control unwanted fish species while ensuring safety for human consumption.