Scuds a.k.a. Gammarus (Freshwater Amphipods)

Freshwater amphipods, commonly known as scuds, gammarus, or sideswimmers are a tiny species of crustaceans resembling tiny shrimp with a compressed body. They are unfortunately better known as pet food for aquarium fish and turtles, while rarely kept as pet themselves.

The natural habitat of freshwater amphipods consists of water streams, rivers, swamps, and lakes, where they feed on decomposing plants and microorganisms. Different subspecis can be found pretty much everywhere across the globe, albeit with different characteristics.

Photo Courtesy of Michal Maňas – Own work, CC BY 2.5

Scuds in the aquarium: keeping and care

The one species of freshwater amphipods that is best suited as an aquarium pet is called Hyalella Azteca and – as the name suggests – originates from Mexico. Scuds are relatively easy to care for. Given their small size, they can easily be cultured in a small cointainer (although they tend to reproduce quickly and in large numbers), and you can keep it in a plastic bucket or bowl if you wish. Make sure to position the tank in a place that receives at least 6 hours of dim sunlight.

Size and appearance

Hylalella Azteca are characterized by a body which looks like that of a compressed shrimp. They don’t have a carapace but rather a hardened flesh that is thicker than that of other types of shrimp. The body is divided in eleven segments with appendages and a tail. Gammarus are generally transparent, but they can change color depending on their diet, with food showing up through their digestive tract in various shades of green. They can also appear brownish in order to camouflage with their environment to hide from predators. Females carrying eggs often assume an orange coloration. Most scuds reach sizes of about 3-8mm, with males being slightly bigger than females.

Life cycle

A newborn gammarus will be only 1mm long but already physically resembling an adult, and will go through nine different evolution cycles molting about once every five days. Average lifespan is one year, with fewer specimen surviving for two years or more. As for other similar species, colder living conditions will slow growth while potentially increasing lifespan, whereas warmer environments will promote fast growth at the expense of lifespan.

Temperature and water parameters

Freshwater amphipods are rather hardy and can survive most winters as long as indoor temperatures don’t fall below freezing. That said, these creatures do prefer slightly warmer environments and won’t reproduce unless temperatures reach around 25°C (75 °F).

Gammarus Diet and Feeding

You can feed your gammarus any kind of shrimp-friendly food, including blenched vegetables and kitchen scraps, fish food pellets, dry leaves and algae. In nature, amphipoda are detrivores and scavengers, so they are pretty good at finding food from their environment – even if you forget to feed them for a couple of days, they will likely be fine as long as there’s enough decaying organic matter in your tank.

Reproduction

Under optimal environmental conditions Hyalella Azteca can reproduce around once a month, with one female producing up to 60 eggs. A newborn shrimplet will reach sexual maturity in about 45 days. In warmer climates these creatures reproduce all-year round, whereas in colder areas they will only reproduce during summer periods.

Scuds with shrimp and ideal tank mates

Scud can be kept in communal tanks but you may encounter issues in which they are competing for resources or being preyed upon by larger fish. If kept in an aquarium with shrimp, gammarus tends to reproduce at a higher rate potentially causing an infestation, and overfeeding on vegetation. There have also been reports of gammarus preying on shrimp fry, which may make the presence of scuds in a shrimp tank undesirable. Keeping freshwater isopods and amphipods together may be more successful as both species are highly prolific yet require low maintainance, and are unlikely to prey on each other. Scuds and freshwater snails are also generally safe to keep in the same tank, and they both make a great addition to a self-sustained planted ecosystem or jarrarium.

Where to buy live gammarus and scud cultures

We are currently curating a list of freshwater amphipods online vendors worldwide.

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Scud (freshwater ampiphods)