Adult males of Gammarus pulex may reach a total length of 21 mm (0.83 in), while females only grow to 14 mm (0.55 in). The adults have a robust appearance; they are typically greyish with markings in dark brown or green.
Gammarus pulex is quite easy to keep alive over long periods – in fact, it will do more than staying alive: it will readily breed and the young Gammarus are small enough (about the size of daphnia) to be eagerly accepted by most fish. They are largely scavengers feeding on dead plant material and other decaying organic matter.
You can keep them outdoors in a bucket or any water container. Make water level about 50 – 100 mm, put Gammarus, watercress, other water weeds, dead leaves, etc. Keep the buckets outside at cool conditions, it must not get too hot in summer. They will survive under ice. They are very hardy and can certainly stand an immediate temperature change from ice at 0°C to 26°C. Gammarus pulex does not like foul water: this will be low on oxygen and the Gammarus will suffocate. So keep the water shallow and do not have too much dead material: plenty of growing plants would seem best. Ideally some plants such as starwort or watercress that the shrimps can eat. The Gammarus breed quite readily in these conditions.