Aquatic Plant Control and Food Chains

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Questions and Answers

Which method effectively discourages the growth of marginal weeds in aquatic settings?

Frequent drainage of run-off from fertile lands

Regular application of organic fertilizers

Using chemical herbicides exclusively

Maintaining a depth of 0.75 – 0.9 m (correct)

Which of the following is a disadvantage of using chemical herbicides in aquatic systems?

They provide slow results

They can be lethal to cultured fish (correct)

They are expensive to apply

They target only emergent weeds

What is a suitable approach for increasing the carrying capacity of a body of water?

Reducing the size of fish species present

Integrating fish farming with other agricultural practices (correct)

Increasing the frequency of water drainage

Limiting the quantity of fertilizers used

What is the approximate percentage of energy lost at each transfer in a food web?

90% Signup and view all the answers

Which chemical is specifically used for the control of filamentous algae?

Simazine Signup and view all the answers

What factor does NOT influence the carrying capacity of a body of water?

Quantity of sunlight Signup and view all the answers

What manual method can be applied to manage floating weeds?

Physical removal by hand Signup and view all the answers

What can be added to increase the natural fertility of a unit of water?

Organic or inorganic fertilizers Signup and view all the answers

What are the three basic nutrients found in fertilizers abbreviated as NPK?

Nitrogen, Phosphorus, Potassium Signup and view all the answers

Which type of fertilizer consists of animal manure and plant waste materials?

Organic fertilizer Signup and view all the answers

What is a known effect of excess nitrogen in water bodies?

Pollution Signup and view all the answers

What must be supplied to increase the carrying capacity of a pond when natural fish food organisms are depleted?

A complete ration of essential nutrients Signup and view all the answers

What factor limits the quantity of feed that can be added to a pond daily?

The efficiency of ecological waste disposal Signup and view all the answers

Which of the following is a type of inorganic fertilizer?

All of the above Signup and view all the answers

What is one of the main contributors to nutrient cycling in aquatic systems?

Bacteria Signup and view all the answers

When overfeeding in aquaculture should be avoided, what is a potential negative outcome?

Detrimental changes in water quality Signup and view all the answers

What is the main benefit of mono-culture in aquaculture?

Ensures continuous growth in poor water quality Signup and view all the answers

Which of the following best describes integrated farming in aquaculture?

Combining fish farming with other agricultural practices for resource efficiency Signup and view all the answers

In polyculture, what is a crucial factor to ensure the successful growth of fish?

Availability of compatible species Signup and view all the answers

Which of the following is an example of double cropping?

Introducing two fish species in different seasons Signup and view all the answers

What is the primary purpose of mono-sex stocking in aquaculture?

To control reproduction and growth rates Signup and view all the answers

Which is NOT a suitable factor when selecting species for polyculture?

Availability of artificial feed Signup and view all the answers

What describes a feature of multi-stage stocking?

Involves progressively larger fish in larger ponds Signup and view all the answers

Natural fish food organisms are essential because they provide:

All essential nutrients for maximum growth Signup and view all the answers

What condition is most likely to improve the growth rate of fish when their standing crop is at a high level?

Providing a ration of sufficient quantity and quality Signup and view all the answers

Which growth pattern do most fish exhibit throughout their lives?

Indeterminate growth Signup and view all the answers

How does population density generally affect the growth rate of fish?

Increased population density decreases growth rate Signup and view all the answers

What factor can adversely affect fish growth when it exceeds the optimum range?

Ambient temperature Signup and view all the answers

Which of the following is least likely to be a factor affecting the growth rate of fish?

Fish color Signup and view all the answers

What is meant by 'length of growing season' in the context of fish growth?

The duration over which fish can accumulate length and weight Signup and view all the answers

What measurement indicates the total length of a fish?

Total length Signup and view all the answers

Which factor does NOT influence the abundance of food available to fish?

Fish species Signup and view all the answers

What does the absolute growth of fish refer to?

The increase in weight or length over time Signup and view all the answers

How is relative growth calculated?

Determining the percentage gain in weight relative to the initial weight Signup and view all the answers

What happens to the basic metabolic rate as fish size decreases?

It increases, requiring more food per unit weight Signup and view all the answers

What occurs to fish growth when food per fish drops below optimum levels?

Growth rate declines and can ultimately stop Signup and view all the answers

In aquaculture, what does 'critical standing crop' refer to?

A state where no weight gain or loss occurs Signup and view all the answers

As the density of fish increases, what happens to the average weight harvested?

It decreases due to limited food availability Signup and view all the answers

Which statement is true regarding the absolute growth rate?

It evaluates weight gain per time unit. Signup and view all the answers

What effect does stocking density have on fish weight during short culture periods?

It can be adjusted to influence final weight. Signup and view all the answers

Study Notes

Aquatic Plant Control Methods

Maintain a water depth of 0.75 to 0.9 meters to deter marginal weed growth.
Reduce silt accumulation by controlling runoff from fertile land.
Regularly desilt ponds.
Erect barriers or mesh filters to prevent plant growth.
Use netting treated with anti-fouling chemicals in cages.
Culture macrophyte-eating fish like grass carp.
Manually remove floating weeds.
Use weed cutters for large individual ponds.
Use herbicides for fast results, but be aware of their toxicity to cultured fish.
- 2,4-D is effective against floating and emergent weeds.
- Diquat is effective against emergent, floating, and submerged weeds.
- Simazine and copper sulfate are effective against filamentous algae.

Food Chain and Energy Transfer

Longer food chains from plants to fish result in lower production.
Food webs are interconnected food chains with less than 100% energy transfer.
Approximately 90% of energy is lost with each transfer in the food web.

Carrying Capacity

Carrying capacity refers to the maximum biomass a body of water can support.
Factors influencing carrying capacity include:
- Water quality.
- Fish size.
- Ration quantity and quality.
- Fish feeding habits.
- Fertilizer quantity and quality.
- Fish species.
Methods to increase carrying capacity include:
- Fertilizer application.
- Feed supplementation.
- Water management.
- Stock manipulation.
- Integrated farming.

Water Fertility and Fertilizer Application

Fertilizer application (organic or inorganic) increases water fertility and natural food organism production.
Nitrogen and phosphorus are crucial nutrients for primary production.
Excess nitrogen can lead to pollution.
Excess phosphorus has no known detrimental effects and is often a limiting nutrient.
Nutrient cycling involves chemical and biological processes with bacteria playing a major role.

Supplemental Feed

Supplemental feed can increase carrying capacity when fish are fully utilizing natural food organisms.
Avoid overfeeding.
When natural fish food is reduced due to fish cropping, a complete ration containing essential nutrients is necessary for increased carrying capacity.
The maximum fish biomass achievable in a unit of water depends on the quality and quantity of ration that can be added without causing dangerous dissolved oxygen levels.
The amount of ration that can be given per unit area per day is limited by the efficiency of the waste disposal and re-oxygenation processes in the ecological system.
Dissolved oxygen (DO) should be maintained at optimal levels.
When growth is limited by waste from feed or biota, monoculture of a fish that can tolerate poor water quality will produce the greatest biomass.

Aquaculture Management Systems

Monoculture:
- Stocking of a single fish species in a pond.
- Mono-size stocking: Stocking fish of a single age or size at a time.
- Multi-stage stocking: Fish of uniform size are stocked in progressively larger ponds.
- Multi-stocking: Stocking different age groups of fish.
- Mono-sex stocking: Stocking fish of only one sex.
- Double cropping: Stocking two species in the same pond during different seasons.
  - Example: Channel catfish - summer, Rainbow trout - winter, Nile tilapia - summer, Blue tilapia - winter
Polyculture: Stocking two or more non-competitive or compatible fish species.
- Grass carp: Omnivorous feeder, roams all strata of the pond.
- Silver carp: Mid-water dweller, feeds on plankton.
- Bighead carp: Mid-water dweller, feeds on zooplankton.
- Black carp: Bottom dweller, carnivore, feeds on mollusks.
- Mud carp: Bottom dwelling omnivore, feeds on benthic animals and detritus.
Factors to consider when choosing species for polyculture:
- Species compatibility.
- Availability of natural food.
- Suitability of environmental conditions.
- Fish demand or price.
Integrated Farming: This system combines fish farming with other agricultural or livestock operations centered around the fish pond.
- By-products and waste from one sub-system are used as inputs for another, ensuring efficient resource utilization.
- Examples: Rice-fish culture, Rice-clam culture, Rice-pig-fish culture, Vegetable-duck-fish culture.

Fish Growth and Nutrition

Natural fish food organisms can supply all essential nutrients for optimal fish growth provided there is enough.
When fish growth slows down due to limited food or other factors, a sufficient quantity and quality of feed can stimulate growth.
Standing crop refers to the biomass present at a particular time.
Fish in poor health grow slower.
Fish species with the same minimum marketable size may grow at different rates. Growth can be positive or negative, temporary or long-lasting.
Fish often exhibit indeterminate growth, meaning they continue growing throughout life if enough food is available.
Growth stoppage in fish is not related to sexual maturity.

Factors Affecting Fish Growth Rate

Population density: Increased population density leads to reduced growth rate.
Genetic variations: Influence growth potential.
Longevity: Life span affects growth rate.
Length of growing season: Longer growing seasons generally lead to better growth.
Water Temperature: Optimum temperature is crucial for growth. High temperatures can reduce growth rate.
Photoperiod: Longer daylight hours generally promote faster growth.
Water Chemistry: Good water quality encourages growth.
Dissolved oxygen levels: Adequate dissolved oxygen is important for growth.
Predator-prey relationship: Presence of predators can affect growth rate.
Food:
- Quantity: Adequate food is essential.
- Quality: Nutritious food supports optimal growth.
- Attractiveness: Palatable food encourages consumption.
- Digestibility: Easy-to-digest food leads to better nutrient utilization.
Biotic Factors: Competition for resources can impact growth rate.
Dominance and Pecking Order: Hierarchies can affect access to food and resources.

Length and Weight Measurements

Total length: Measured from the tip of the snout to the tip of the longest portion of the caudal fin.
Standard length: Measured from the tip of the snout to the caudal peduncle.
Fork length: Measured from the tip of the snout to the middle portion of a forked caudal fin.
Body depth: Measured from the dorsal side to the ventral side at the deepest body portion.

Weight Measurements:

Total weight: Fish weight when no part is removed.
Bulk weight: Total weight or biomass.

Growth Parameters

Absolute growth: Difference between initial and final length or weight. - Absolute growth = Wf - Wo (Wf = Final weight, Wo = Initial weight)
Absolute growth rate: Gain in weight or length per unit time. - Absolute growth rate = (Wf - Wo) / Days of culture
Relative growth: Percentage weight gain of fish in relation to its initial weight. - Relative growth = ( (Wf - Wo) / Wo) x 100
Relative growth rate: Percentage weight gain of fish in relation to initial weight per unit time. - Relative growth rate = ( (Wf - Wo) / (Wo x Days of culture) ) x 100

Additional Considerations

Smaller fish have higher metabolic rates and require more food per unit of body weight for maximum growth.
Increasing fish density reduces food availability per fish and can limit growth.
At a critical standing crop, higher stocking density leads to lower average fish weight after a culture period.
Stocking density and final fish weight can be adjusted using stocking numbers for short periods of time.

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Description

This quiz covers essential methods for controlling aquatic plants as well as the dynamics of food chains and energy transfer within aquatic ecosystems. Explore how to manage plant growth and understand the interconnectedness of food webs in water bodies. Test your knowledge on these critical environmental topics.