Science 7–10 · Year 7

Brine shrimp hatching: the effect of salinity on an abiotic tolerance

Science understanding: Biological sciences

PracticalLow risk

The idea

An abiotic factor sets a range within which an organism can complete part of its life cycle, and hatching success falls outside that range.

Safety card

Low riskAn adult supervises

Hazards

Cyst dust is an irritant if inhaled
Electrical air pump near water

Controls

Weigh cysts in a still-air spot and avoid puffing them
Keep the pump above the water line
Wash hands
Brine shrimp are not native: freeze then bin the cultures; never pour them into a waterway

Note

No hazardous chemicals; record a RiskAssess risk assessment for the activity as school procedure requires.

What you need

Brine shrimp (Artemia) cysts, 1 g, from an aquarium supplier
Aquarium sea salt and distilled or dechlorinated water to make 250 mL each of 0, 5, 15, 35, 60 and 90 g/L solutions (weigh 0, 1.25, 3.75, 8.75, 15.0 and 22.5 g into 250 mL)
Six clear 300 mL containers per group, labelled, with lids loosened; the FAO manual reports that containers without a conical bottom hold dead spots where cysts and nauplii accumulate and suffer oxygen depletion, so the airline sits at the centre of the bottom of each container
An aquarium air pump with a gang valve and an airline run to the bottom of each container, left on for the whole incubation; the FAO manual states that the aeration must hold dissolved oxygen above 2 mg/L, preferably 5 mg/L, which hourly hand stirring cannot do overnight
Thermometer; a warm spot or heat mat holding 25 to 28 °C; a desk lamp on the containers
pH strips (the water should read pH 8 or above; add a pinch of sodium hydrogencarbonate if lower)
1 mL pipettes, 10 mL measuring cylinders, a counting dish with a grid, and a x10 hand lens or stereo microscope

How to do it

Make the six salinities and check that each reads pH 8 or higher and 25 to 28 °C.
Add 0.125 g of cysts (0.5 g/L) to each container, start the aeration and switch on the lamp.
After 24 h, stir gently and draw three separate 1 mL samples from each container. Count the swimming nauplii in each; if there are too many to count, add the 1 mL sample to 9 mL of the same salt solution, count 1 mL of that and multiply by 10. Record the mean per mL.
Repeat the count at 48 h.
Plot mean nauplii per mL against salinity for both times.
Run three replicate containers per salinity across the class and combine the data.

What you should see

The FAO Artemia manual gives an optimal hatching salinity that varies by strain but is generally 15 to 70 g/L (the same page also gives 5 to 35 g/L as a range for optimal hatching), and a threshold of about 90 g/L for most strains, above which the cysts cannot take up enough water to hatch, so expect similar high counts across 5 to 60 g/L and few or no nauplii at 90 g/L. Report the 0 g/L container as measured. FAO's benchmark for a good cyst batch in 33 g/L seawater at 25 °C is first nauplii after 12 to 16 h and the last within 8 h after that, so the 24 h count should capture most of the hatch. FAO gives 100,000 to 270,000 nauplii per gram of commercial cysts, which at 0.5 g/L is about 50 to 135 nauplii per mL for a good hatch, hence the dilution step. Newly hatched nauplii are 470 to 550 micrometres long, large enough to count with a hand lens. The learner knows the practical worked when replicate counts at one salinity are close to each other compared with the differences between salinities, and the plot shows a plateau then a fall.

What changes

What you change: Salinity (g/L)
What you measure: Number of swimming nauplii per mL at 24 h and 48 h
What you keep the same: Temperature (25 to 28 °C)
Cyst mass (0.125 g per 250 mL)
Light (lamp on all containers)
Continuous aeration at the same rate in every container
pH at or above 8

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

More salt is always worse for a salt-water animal.
Cysts are dead because they are dry.
If nothing hatched at 0 g/L the cysts were faulty, rather than the conditions.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7–10 Syllabus (2023)SC4-LIV-01 SC4-WS-03 SC4-WS-04 SC4-WS-06
Australian Curriculum v9AC9S7U02AC9S7I02AC9S7I03AC9S7I05

Sources

The pages the author read to write this activity.

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