The effect of temperature on the hatching success of brine shrimp

Question 1

Independant variable

Answer 1

temperature

Question 2

Dependant variable

Answer 2

number of hatched shrimp

Question 3

Other variables to be controlled (5)

Answer 3

• Light intensity
• pH
• salt content
• presence of chlorine from tap water
• oxygen concentration

Question 4

Equipment (8)

Answer 4

• Brine shrimp egg cysts
• 2 g sea salt for each treatment de-chlorinated water for each
• treatment
• beakers
• Water baths or incubators
• Forceps
• Bright light
• pipette

Question 5

Outline the method

Answer 5

Decide on a range of temperatures from 5 °C to 35 °C to be tested. Place 2 g of sea salt into a 100 cm3 beaker. Add 100 cm3 of de-chlorinated water and stir until the salt completely dissolves. Label the beaker with sea salt and the temperature at which it will be incubated. Place a tiny pinch of egg cysts onto a large sheet of white paper. Wet the piece of graph paper using a few drops of salt water. Dab the paper onto the white sheet to pick up approximately 40 eggs. Use a magnifying glass to count the eggs. Put the paper with the 40 eggs into the beaker (eggs-side down). After 3 minutes, use a pair of forceps to gently remove the paper, making sure that all the egg cysts have washed off into the water. If possible replicate the treatments. Incubate the beakers at the appropriate temperatures, controlling exposure to light as far as possible. The next day count the number of hatched larvae in each of the beakers. To do this, place a bright light next to the beaker. Any larvae will swim towards the light. Using a fine glass pipette catch the brine shrimps and place them in a small beaker of salt water. Brine shrimps are very delicate and care must be taken when handling them. Record the number of larvae that have successfully hatched at each temperature.

Question 6

Possible evaluation issues (8)

Answer 6

• ethics of hatching shrimp under different conditions
• use of animals in experiments
• effect of light intensity, may be a difference in light in each sample
• fluctuating temperatures
• not accurate salt measurements
• may not have counted exactly 40 eggs
• may miss seeing some of the baby shrimp
• some eggs may not be viable anymore and wont hatch