Question 6
(a) State four likely causes of economic losses of smoked-dry clarias.
(b) A farmer constructed a fish pond measuring 10 m by 20 m by 1.5 m length, breadth, and depth respectively. He discovered that the pond water has a pH of 5.5.
- State one way in which the fish farmer could improve the pond water pH.
- List three substances that the farmer could use to improve the pond water pH.
- If the recommended quantity of the substance needed to improve the water pH is 2,000 kg/ha, what quantity would the farmer require for the pond?
- If the stocking rate of the pond is 10 fish/m2, what is the quantity of fish required to be stocked in the pond?
(c) Name four fish species that could be cultured in Nigeria.
(d) Mention the water quality parameter that is measured using each of the following instruments:
(i) Secchi Disc;
Observation
Most of the candidates did not attempt this question and few that did could not mention the likely causes of economic losses of smoked dry Clarias
The expected answers are as follows:
(a) Likely causes of economic losses of smoked-dry Clarias
- Breakages
- Insects / worms / larvae infestation
- Mould / fungi infestation
- Contamination by rodents
- Poor storage conditions / high humidity
- Poor handling
- Poor packaging
(b) (i) One way to improve pond water pH
By liming the pond
(ii) Substances that could be used to improve pond water pH
- Calcium carbonate
- Calcium hydroxide
- Calcium oxide / Calcium IV oxide
- Wood ash
(iii) Calculation of quantity of substance required to improve pond water pH
Area of pond = 10m x 20 m
= 200 m2
Liming rate = 2000 kg/ 10,000 m2
Quantity required for 200 m2 = 200 m2 x 2000 kg
10,000 m2
= 40 kg
(iv) Calculation of quantity of fish required to stock the pond
Area of pond = 10 m x 20 m
= 200 m2
Stocking rate = 10 fish / m2
Quantity of fish required to stock 200 m2 Pond = 200 m2 x 10 fish
1 m2
= 2,000 fishes
(c) Culturable fish species in Nigeria
- Tilapia
- Clarias
- Heterobranchus
- Heterotis
- Carp
- Heteroclarias
- Water quality parameters measured using the following instruments
Secchi disc: Turbidity / Transparency / Water clarity
Thermometer: Temperature