Tillingbourne Riverfly Monitoring

Freshwater Shrimp (Gammarus)

Freshwater Shrimp are by far the most prolific invertebrate species found in the River Tillingbourne at Albury Park. They have been present in large numbers throughout the year, with often over 1,000 in our 3-minute kick sample.

Colours range from olive, grey and dull orange. An average body length would be 10-12mm but often we see 'whoppers' of around 15mm.

They can move very quickly and when doing so, the body is often straight. At rest they assume the characteristic curved body that we normally associate with shrimp. For imitative fly-tying anglers it would be a good idea to tie a few with straight bodies with and without the red spot.

There seems to be some confusion about what causes red spots in gammarus - is it eggs or a parasite?

I have been told it is caused by a parasite called pomphorhynchus and a 'google' search seems to support this. At Albury sometimes we have around 5% of the sample with red spots, at other times very few.

The specimen in the photograph was found in middle beat in April 2005 along with many others with red spots.