I have a question, what is a scud exactly?
Freshwater amphipods, also known as scuds, sideswimmers, gammarus, baby shrimp or ohgrosswhatisthat, are small crustaceans that are abundant in many aquatic habitats and form a major part of the diet of many small fishes. While they can swim, scuds tend to spend most of their time clinging to surfaces or wedged into interstitial spaces.
Scuds are grazers and detritivores that feed on a variety of decaying matter, aufwuchs and biofilms and can help keep your tank clean if they survive. They make great additions to planted tanks, refugia, and large filters.
Q. What do scuds look like?
A. Scuds are laterally compressed, vaguely shrimp-like animals measuring usually less than 3/4" in length. They have a characteristic C-shaped posture, and unlike shrimp and crayfish, they lack claws (chelae) and tail "fins" (uropods). When disturbed, they swim in often circuitous routes but at a relatively steady speed unlike the jerking flight of many crustaceans. They may be various shades of gray, brown, or pinkish.
Q. What are they good for?
A. Scuds are relished by numerous aquatic predators including cichlids, goldfish, minnows, darters, killifish, juvenile sunfish, aquatic salamanders, juvenile turtles, and crayfish.
Q. Where can I find scuds?
A. Scuds occur in both slack and flowing water environments of all sizes and everywhere from bottomland swamps to mountain brooks to cave pools. Scuds reach highest abundances where food and structure are both readily available. Examples include leaf mats, dense tree roots, and thick submersed or floating vegetation. They can also be found in gravel and muck, but seem to be less concentrated in those habitats.
When I want large numbers of scuds, I go to a spring run I know that has dense mats of watercress, duckweed, and riccia. Holding a net immediately downstream of a mat, I give it a vigorous shaking dislodging hundreds of scuds which then drift into my net.
Q. What do I need to culture scuds?
A. Not much is needed to culture scuds. You need, of course, a container to house them, dechlorinated water, and food. In a small container, you will also need to maximize oxygen levels. Containers as small as one gallon or even less may be used, but the water chemistry in these tiny containers is easily knocked off balance before you even know it. I prefer to use 10 gallon containers or larger if at all possible. It is wise to maintain more than one colony in case one crashes or overharvested and needs time to recover.
I do not use filtration in my colonies. Smaller containers however are more likely to need filtration. If you decide to use filtration, a gentle air-driven system such as a sponge or undergravel filter is best. Power filters are likely to suck in scuds and possibly mangle or strand them in the filter chamber.
Water chemistry is not very important. Hardness, pH, and so on matter little. Like all other invertebrates, scuds are sensitive to copper. Room temperature is fine. I like to start a colony with scuds from several sources to ensure that at least one group will thrive in the conditions provided.
Q. What do I feed my scuds?
A. Scuds are catholic eaters that like fish food, old filter sponges, dead or dying plants, vegetable scraps, and so on. They will even eat paper towels. A scud colony can act as a convenient waste disposal as well as a food source, although you must be careful not to foul the water by adding too much food. Also, keep in mind that whatever the scuds eat, your fish will eat at second hand, so keep your food source clean.
Q. Can I keep anything else in my scud colony?
A. Many other invertebrates will thrive in a scud tank, including daphnia and other cladocerans, copepods, isopods, and snails. My colony is periodically invaded by midges. I have not tried raising blackworms, tubifex, or shrimp in a scud colony, so I can't say how successful that would be.
I hope this was helpful. If anyone else with scud experience would like to add to this, please feel free.