Study the specimens: Specimen L (NPK Fertilizer): Specimen M (Tilapia Fish): Specimen N (Litmus Paper):

(a) Identification of specimens

• Specimen L: NPK fertiliser
• Specimen M: Tilapia fish
• Specimen N: Litmus paper

(b) Identification of specimens O and P using litmus paper

Litmus paper is used to test whether water is acidic or alkaline:

• Specimen O: acidic pond water, if it turns blue litmus paper red.
• Specimen P: alkaline pond water, if it turns red litmus paper blue.

(c) Pond in which tilapia will survive better

Tilapia will survive better in specimen P, the alkaline pond water. Tilapia generally grows best in water that is near neutral to slightly alkaline. Acidic water can stress fish and reduce their growth and survival.

(d) Relevance of NPK fertiliser in tilapia production

NPK fertiliser supplies nutrients, especially nitrogen and phosphorus, to the pond. These nutrients encourage the growth of phytoplankton and other aquatic organisms, which form natural food for tilapia. This can improve fish growth and yield.

(e) Pond management practices to improve acidic pond water for tilapia production

• Apply agricultural lime to the pond to reduce acidity and raise the pH.
• Drain or flush out excessively acidic water and replace it with clean water of a suitable pH.

(f) Ways of controlling loss of tilapia on a farm

• Fence or secure the farm and pond area to prevent theft.
• Use nets, screens, or barriers to prevent predators such as birds, snakes, and frogs from entering the pond.
• Maintain good water quality and control diseases through proper feeding, correct stocking density, and prompt removal of sick or dead fish.

(g) Harvesting methods for tilapia

• Partial harvesting: use a seine net or cast net to catch only market-sized fish, leaving smaller fish in the pond to continue growing.
• Complete harvesting: drain the pond and collect all the fish.

Examination reminder: When litmus paper is used, remember that blue litmus turns red in an acid, while red litmus turns blue in an alkali. For fish ponds, acidic water is commonly corrected by liming.