MP Board · Class 9 · Science · Improvement in Food ResourcesSolve the numerical problem in Part A and answer the theoretical question in Part B regarding Pisciculture and Composite Fish Culture System: Part A (Numerical):\nA fish farmer practices composite fish culture in a $2\text{-hectare}$ freshwater pond. The pond is stocked with fish fingerlings at a density of $6,000\text{ fingerlings}$ per hectare. Due to efficient management practices, the overall survival rate of the fingerlings is $85\%$. At the end of the culture period, each harvested fish attains an average body mass of $1.2\text{ kg}$. Calculate the total number of fingerlings stocked in the $2\text{-hectare}$ pond. Calculate the total number of surviving adult fish harvested from the pond. Calculate the total fish yield (in kg) produced and the total revenue earned if the market price of fish is ₹$150$ per kg. Part B (Theoretical):\nWrite a detailed note on Composite Fish Culture addressing the following points: Explain the underlying principle of composite fish culture and identify the specific ecological feeding zones of five common fish species used in this system (Catla, Silver Carp, Rohu, Mrigal, and Grass Carp). State two key economic advantages of this polyculture system. Identify the major constraint faced in composite fish culture regarding seed quality and explain how induced breeding using hormonal stimulation resolves this problem.

Part A (Numerical Solution)

1. Total Fingerlings Stocked:

• Stocking density = $6,000\text{ fingerlings/hectare}$
• Area of pond = $2\text{ hectares}$ $$\text{Total Fingerlings Stocked} = 6,000 \times 2 = 12,000\text{ fingerlings}$$

2. Total Surviving Adult Fish Harvested:

• Survival rate = $85% = 0.85$ $$\text{Harvested Adult Fish} = 12,000 \times 0.85 = 10,200\text{ adult fish}$$

3. Total Fish Yield and Total Revenue:

• Average body mass per fish = $1.2\text{ kg}$ $$\text{Total Fish Yield} = 10,200 \times 1.2 = 12,240\text{ kg}$$
• Selling price per kg = ₹$150$ $$\text{Total Revenue} = 12,240\text{ kg} \times \text{₹ } 150 = \text{₹ } 18,36,000$$

Part B (Theoretical Solution)

1. Principle and Ecological Feeding Zones in Composite Fish Culture\nComposite fish culture (polyculture) is a system where a combination of five or six different fish species (both indigenous and exotic) are cultivated together in a single fish pond. The species are chosen such that their food habits do not conflict, allowing complete utilization of nutrients across all pond zones.

• Catla (Indigenous): Surface feeder; feeds on surface zooplankton.
• Silver Carp (Exotic): Surface feeder; feeds efficiently on microscopic phytoplankton.
• Rohu (Indigenous): Column feeder; feeds on organisms present in the middle zone of the water column.
• Mrigal (Indigenous): Bottom feeder; consumes detritus, decaying organic matter, and benthic organisms at the pond bottom.
• Grass Carp (Exotic): Vegetative feeder; feeds on aquatic weeds and macro-vegetation.

2. Key Advantages of Composite Fish Culture

• No Food Competition: Since every species occupies a distinct ecological niche and feeding zone, inter-specific competition for food is avoided.
• Maximization of Yield: Available food resources across all water levels are fully exploited, resulting in significantly higher fish production per unit pond area compared to monoculture.

3. Seed Availability Problem and Solution via Induced Breeding

• Major Problem: Most cultured fish species breed only during the monsoon season in riverine ecosystems. Obtaining wild seed (spawn) from natural sources often leads to contamination with undesirable wild species, creating a major shortage of pure, high-quality fish seed.
• Solution (Induced Breeding): To overcome this limitation, fish are artificially bred in controlled hatchery ponds using hormonal stimulation (hypophysation). Pituitary gland extracts or synthetic hormone injections are administered to mature male and female broodfish. This stimulates gamete release and ensures a reliable, pure, and high-quality supply of desired fish seed throughout the breeding season.