pH

• Defined as the negative logarithm of the hydrogen ion activity and indicates whether the water is acidic or alkaline in reaction and is measured on a scale of 0-14.
• The optimum range of pH for fish culture is 6.8-8.6, broadly 6.5-9.

pH measurement

a. pH indicator paper:

• A thin strip of paper ( Such as chemically treated litmus paper) is partially dipped into the water to be tested.
• The color of the paper changes and this new color is compared to a color chart, which gives the pH value according to the color obtained.

b. Color comparator:

• Cheap water-testing kits can be bought from special chemical suppliers.
• They usually include several liquid indicators.
• A few drops of one of these colors are added to a small water sample, and the new color of the solution is compared with a set of standard colors supplied with the testing kit.

pH meter

• Provides the easiest way for determining the water pH, even in the field, but it is relatively expensive.
• The pH value is directly read from the meter after placing the glass electrodes in a water sample.
• Such electrodes are very fragile and should be well protected when being transported.
• Should be accurately calibrated in buffer solutions of known pH, at regular intervals.

Effects of pH on fish

a. Effects of low pH:

• Reduces appetite
• Inhibits fish growth, ceases reproduction
• Reduces tolerance to toxic substances
• Excessive production of mucus on the gills which interferes with respiration.
• Attacks of parasites and diseases
• Acid death

b. Effects of high pH

• Damage to Cornea and lens of eyes
• Damage gill filament
• Disturb the blood acid-base balance
• Slow growth rate
• Increase ammonia toxicity
• Alkaline death

pH management in Fish Pond

• Low pH: Liming the pond @500-1000 kg/ha/yr depending upon pH.
• High pH: Use carbonic fertilizers, nitrogenous fertilizers, etc.