Page 287 - Agriculture_Form_Three

Agriculture for Secondary Schools

elbow, the palm should be visible). Transparency should be measured in the
shadow and should be 25 - 60 cm.
(v) Water colour: Light greenish, brown-green or greenish water is most suitable
for fish culture. Dark brown and dark green are not good for fish.
(vi) Ammonia (NH ): Ammonia exists in two forms: un-ionised NH which is
3
3
highly toxic and ionised NH which is less toxic. Avoid concentrations of un-
+
4
ionised ammonia greater than 0.1 mg/L. Ammonia can be measured using test
kits. Alternatively, it can be detected by its pungent smell.
(b) Measures to take when water quality parameter falls outside its optimal
range
Measures that can be taken when water quality parameters fall outside its optimal
range are summarised in Table 12.1.
Table 12.1: Measures to be taken when parameters fall outside its optimal range
S/N Observation Possible measures to be taken
1. High temperature (> 30 °C) Exchange water
2. Low dissolved oxygen (i) Increase water exchange
(ii) Stop feeding until corrected
(< 3.5 ppm AM, < 5 ppm
PM) (iii) Watch for symptoms of parasites/diseases
(iv) Beating/stirring of water-moving water
increases DO
3. Low pH (< 6) (i) Add alkaline buffer (sodium bicarbonate,
lime)
(ii) Reduce feeding rate
(iii) Check ammonia concentration
4. High ammonia (i) Exchange water

(ii) Reduce feeding rate
(TAN > 0.25 mg/L) or
(iii) Watch for symptoms of parasites/disease
pH higher than 9
5. Transparency too low (i) Exchange system water
(ii) Reduce feeding rate
(< 30 cm)
(iii) Watch for symptoms of parasites/
diseases
6. Dark green or brown colour (i) Exchange water
(ii) Reduce feeding rate
(iii) Measure DO

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