Aquaculture textbook
Chapter 3: Experimental design - Setting up a fair trial


Example in detail

In a feed trial the independent variable is the amount of food given to stock and the dependent variable is the stock's weight. All other parameters need to remain constant.

A closer look reveals how the trial's parameters can now be expanded upon and an example is given of the type of information that needs to be gathered and recorded.

parameters Constant or Variable Example
What's the trial's goal? N/A

To decide whether Diet A is more efficient than Diet B.

Part 1: Find the overall average food conversion ratio (FCR) for each diet.

Part 2: Find the food cost per kilogram for each diet.
How is it to be achieved?
 see below Determine the constants and variables (dependent and independent) so a procedure can be designed.
  • Determine the number of ponds to be used.
 constant Diet A - three ponds
Diet B - three ponds
  • Time period of trial.
 constant 16 weeks
  • Interval.
 constant Daily
  • Conditions, for example, water quality and quality of feed.
 constant See Chapter 1: Nutrition, and Chapter 4: Production, of the Aquaculture Textbook.
  • Number of sample stock in each pond.
 constant Pond 1-3 - 1,000 each (Diet A)
Pond 4-6 - 1,000 each (Diet B)
  • Take a sample of the stock's initial average weight for each pond and record data. Samples are periodically taken and measurements (weight) made throughout the trial.
 independent
variable		 Pond 1 - 20.2 g
Pond 2 - 21.0 g
Pond 3 - 22.5 g
Pond 4 - 20.3 g
Pond 5 - 21.4 g
Pond 6 -21.9 g
  • The type of feed given to stock each day in each pond.
 dependent
variable		 Diet A: Pond 1-3
Diet B: Pond 4-6
  • Record how much feed is given to stock each day in each pond. This is used in the calculation of the overall average FCR for each diet.
 constant Pond 1 - Day 1: 454g
Pond 2 - Day 1: 465g
Pond 3 - Day 1: 458g
Pond 4 - Day 1: 420g
Pond 5 - Day 1: 457g
Pond 6 - Day 1: 385g
  • Use a formula to calculate the morality rate for each pond.
 constant See Chapter 2: Measurements of the Aquaculture Textbook.
  • Use a formula to calculate the daily survival rate for each pond.
 constant See Chapter 2: Measurements of the Aquaculture Textbook.
  • Use a formula to calculate the food conversion rate(g) for each pond.
 constant See Chapter 2: Measurements of the Aquaculture Textbook.
  • Use a formula to calculate the average FCR for each diet.
 constant See Chapter 2: Measurements of the Aquaculture Textbook.
  • Compare Diet A and B using FCR figures, cost per kg and food cost per kg.
 constant
See Chapter 2: Measurements of the Aquaculture Textbook.

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