Observation

Most of the candidates mentioned Turbidity, transparency, and clarity for specimen A and went on to mention Dissolved Oxygen for Specimen B. Many candidates could not describe the use of Specimen B (Dissolved Oxygen) in sequence as required in Question 1.

The expected answers were:

1. Water Quality Parameters measured by Specimens A and B           

Specimen A ( Secchi Disc)           =  Turbidity/transparency/ water clarity
Specimen B (DO Meter)               =   Dissolved oxygen (DO)

(b)        Labelled diagram of a Secchi Disc                

(c)        How Specimen B (Dissolved Oxygen meter) is used in a fish culture

• Gradually lower the probe into the pond water
• Move the probe in the water to release any air bubbles
• Continue to move the probe
• Wait for the DO meter readings to stabilize and note the reading/value
• Repeat the procedure to get a second reading /value
• Find the average of the two readings/values   
• Record the average as the DO content of the pond

                                                                                                           
(d)       Effects of specimen B (Dissolved Oxygen meter) reading below 3.0mg/l on fish
-           Fish piping for oxygen at the surface of the pond
-           Reduced feed intake by the fish / loss of appetite
-           Reduced activities / fish become sluggish / weak
-           Mortality/ death
-           Fish hanging vertically at water surface
-           It can cause increased fish stress / susceptibility to diseases