Question 5
- The pH of a fish pond water is 5.0
- State two effects that the pH could have on Clarias spp.
- Mention two ways through which the pH could be corrected. [4 marks]
- The diagram below illustrates the measurement of a water quality parameter of a fish pond. Study it carefully and answer the following questions:
- Name the water quality parameter that is measured.
- List four steps that should be taken when using the instrument labelled X in the diagram. [5 marks]
- (i) Give three reasons why trawling is mostly used in the sea.
(ii) Name three other fishing gears that could be used in the sea. [6 marks]
- State three reasons why an old fish pond is flushed before stocking. [3 marks]
- Give two examples of fish food. [2 marks]
Observation
This question was attempted by many candidates and their performance was good. Many candidates were able to stating the action instead of the gear in Question 5(c). In Question 5(e), fish food seems to be poorly understood as the candidates were listing different feeds given to the fish instead of what the Fish eats naturally such as Phytoplanktons and Zooplanktons.
The expected answers are as follows:
(a) (i) Effects of pH 5.0 on Clarias spp
- Poor feeding
- Poor growth
- Restlessness/sluggishness
- Death
(ii) Ways in which pH 5.0 could be corrected in a fish pond
- Liming/addition of CaCO3/ Ca(OH)2/ CaO
- Replacement of pond water
(b) (i) Water quality parameter being measured
- Temperature
(ii) Steps that should be taken when using X (Thermometer)
- Ensure that the meniscus is at the normal level
- Dip the bulb of the thermometer into the fish pond water at a depth of
about 15 – 20cm
- Wait for a short time to ensure the meniscus is stable
- Take the reading
- Repeat the procedure
- Find the average
(c) (i) Reasons why trawling is mostly used in the sea
- Trawling operation requires deep water
- Minimal obstruction
- Ability to catch large quantities of fish
- Highly mechanized
(ii) Other fishing gears that could be used in the sea
- Long line - Harpoon
- Pole and line - Purse seine
- Gill net - Drift net
(d) Reasons for flushing an old fish pond before stocking
- To clear pond of debris
- To ensure the removal of left over fish in the pond
- Removal of excess silt/mud
- Removal of old/used polluted water
- Eliminates predators
- Eliminates disease causing pathogens
(e) Examples of fish food
- Algae (phytoplankton)/vegetables/plant matter/macrophytes
- Zooplankton/Aquatic organisms/animals