Head to head
Freshwater Shrimp vs Water Louse
Freshwater Shrimp
VS Water Louse
The freshwater shrimp and the water louse are two small crustaceans that often turn up together when a pond net or stream kick sample is emptied into a tray.
| Freshwater Shrimp | Water Louse | |
|---|---|---|
| Scientific name | Gammarus pulex | Asellus aquaticus |
| Group | An amphipod, with a curved, sideways-flattened body | An isopod, with a flat, oval body made of overlapping plates, related to the woodlouse |
| Size | About 1 to 2 cm long, grey, greenish, or brown | Usually 1 to 2 cm long, grey-brown, with seven pairs of legs |
| Movement | Swims on its side with a wriggling movement, and curls up when removed from the water | Crawls over mud, stones, and weed rather than swimming |
| Diet | Shreds fallen leaves, and eats the fungi and bacteria on them, along with algae and dead animals | Eats rotting leaves, algae, and dead plant and animal matter |
| Mating | The male carries the female beneath him for days before she moults, and then mates with her | The male holds on to the female and carries her for several days before she moults and they mate |
| Water quality | Sensitive to pollution, so large numbers signal a healthy stream | Can live in water that is rich in nutrients or low in oxygen, where many other invertebrates cannot |
| Conservation status | Not Evaluated, but abundant in clean streams across Europe | Not Evaluated, but abundant in ponds, lakes, canals, and slow rivers across Europe and northern Asia |
Freshwater Shrimp vs Water Louse: common questions
Which one is a sign of clean water?
The freshwater shrimp, which is sensitive to pollution, so large numbers in a stream suggest the water is healthy.
Is the water louse related to a woodlouse?
Yes, it is an aquatic isopod, related to the woodlouse, whereas the freshwater shrimp is an amphipod.
How do they swim?
The freshwater shrimp swims on its side, while the water louse mostly crawls over mud, stones, and weed.