I have been correctly told that the critters are scuds, and I have posted a few links to pictures and some info I found from some sites. Last night I crept to the tank in the dark with a flashlight and the number of scuds along the gravel and on my driftwood was astounding. I wonder how many I send to their doom when I sweep my gravel?!
Most of the info on the net is fly fishing related. Apparently, scuds are ubiquitous throughout the world. They are a major food source for many fish. I also found a few links discussing their use as a grow-your-own live food source for the aquarium. The smallest fish in my tank is a 5" mono, so I guess the small size saves them from attention. On the other hand, I haven't seen any scuds larger than 1/8". . .
http://www.lfscultures.com/p11.html
http://users.myexcel.com/dolfnlvr/Scuds/scuds.html
Description: Scuds are a small freshwater crustacean shrimp like in apperance easily cultured in small fish tanks. They like to eat plant matter but will live happily on most fish foods. Uses: Scuds make an excellent food for most species of adult fish including smaller species. Size: Upto 1cm Ease of Culturing: Easy to culture with minimal maintenance.
Culturing Method:
Culturing container: Scuds can be cultured in small fish tanks or plastic buckets filled with freshwater.
Water requirements: Water for scuds should be aged, water from an existing aquarium is fine. P/H is not critical.
Water temperature: Scuds can live in a wide range of temperatures but do best when cultured at 65 to 85 degrees f.
Aeration: Gentle aeration is desirable for scud cultures although not essential.
Lighting: Some natural light is required.
Feeding: Feed scuds on live plants and leaves or any tropical fish flakes or floating fish pellets. A combination of both is best.
Additional requirements: Scuds will do best when provided with plenty of hiding places and things to cling to. This will increase the surface area and the scud population. You could place gravel on the bottom of the culturing container and plant some live plants this would provide hiding places and food. There are any number of different things you could use to provide hiding places for scuds just use your imagination. Broken clay plant pots are ideal.
Maintenance: The culture should have a partial water change every 2-3 weeks.
Gammarus, also known as Scuds, is a shrimp-like crustacean. It is an easy to culture livefood that is an excellent size for many larger tropical fish. Even adult guppies can eat scuds. Cichlids and many killifish love them. Size: This crustacean reaches about 1cm (0.4 in.). Description: This shrimp-like, freshwater crustacean lives on decaying plants and detritus also eating algae and other microorganisms. It is gray to green in color. Environment: This species survives happily in aquarium quality water. It can tolerate temperatures as low as 0 degrees C (32 degrees F) and high as 35 degrees C (95 degrees F) but prefers temperatures ranging from 20-30 degrees C (68-86 degrees F). pH is not important. Culture containers (the author prefers 32 gallon plastic trash cans, preferably yellow or white colored) should be aerated and provided a good food source, such as plant cuttings or tree leaves. Geographic Range: Various species in North America, Europe and Asia. Uses: This livefood species is an excellent livefood for most large tropical fish. It has the advantage of surviving aquarium conditions indefinitely so that it can be fed in abundance without fear of water fouling (do not, however, feed too many without adequate aeration since this organism will compete with fish for oxygen).
A scud looks something like a miniature shrimp. Some species reportedly grow to be close to an inch long but the ones used in aquariums as live food are smaller than that - slightly longer than 3/8ths of an inch. They can walk both in and on the detritus that accumulates at the bottom of lakes, streams, and other bodies of water (There are salt water forms too). They can also walk on land but they rapidly dry out and die. Scuds are strong swimmers and zip away at top speed when disturbed often swimming on their sides and are thus nicknamed sideswimmers. Scuds are scavengers and will attack and eat decaying plant material but if not overcrowded will not harm healthy aquarium plants. They feed similarly to shrimp and crabs by scraping material off surfaces and/or filtering small particles with bristle covered limbs from the water.
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Amphipoda
Order: Gammaridae
Family: Gammarus
