Freshwater Amphipod – Species Profile

Gammarus_roeselii
Freshwater Amphipod “Scud”. Source: wikimedia.

Also called “scuds” or “side-swimmers”, amphipods is a collective term for many species of aquatic crustaceans. Many amphipods you will find in the freshwater aquarium hobby are of the genus Gammarus or Hyallela. There are also numerous saltwater species.

Care Level: “Where did these come from?” Easy
Preferred Water: pH 6 to 8, soft to hard
Ideal Temperature: 65 to 75 °F (12.8 – 22.2 °C)
Maximum Size (depending on species) : 0.25″ to 0.5″ (6.35 mm to 12.7mm)
Average Lifespan: 1 to 1.5 years

Distribution

Amphipod species exist all around the world in both fresh and saltwater habitats. They prefer places with ample litter to forage through and places to hide. Freshwater species can be found in many different habitats including ponds, lakes, and streams.

Foreground: amphipod eating decaying leaf.

Diet

Amphipod diet varies by species and habitat, but many are detritivores, meaning they eat waste, decaying matter, and basically anything that can be loosely defined as “food.” They will often feed on the dead of their own species, and will sometimes catch and eat organisms smaller than themselves. In my experience maintaining scud colonies in my tanks as well as in their own tanks, I have learned that scuds will eat pretty much anything, depending on how desperate they are. I have kept ramshorn snails and scuds together in a colony tank, only to find that once their numbers became great enough, the scuds consumed the snails. So, keeping their population under control and well fed is the key to success.

Amphipods will also consume various species of plant material. They prefer soft plant matter, usually preferring dead or dying leaves. They will eat some healthy plants with soft leaves, like staurogyne repens. They also consume java moss, though with less enthusiasm. Before adding a scud colony to your planted tank, you should take time to research whether or not they may consider your plants food.

The will eat all kinds of fish or shrimp food and decaying plant matter, which makes them very easy to keep in captivity.

As I continue to experiment with keeping scuds in my aquariums, I will add to the lists below, detailing my observations of what plants they will readily eat and which they don’t seem to care for. In my observations, it seems that the density of the colony population plays a huge role in how destructive their plant eating habits are. If you are keeping scuds in a planted tank, try to keep their numbers under control either through predation or manual removal.

Plants Scuds Will Eat*

Java Moss – when no other food is available. They will eat the leaves off of the stem and leave the stem behind.

Staurogyne repens – enthusiastically!

Rotala rotundifolia – if no other food is available or plant is severely weakened

Dwarf Sagittaria – they will chew on new leaves, but seemingly only when no other option is available

Anubias barteri – they will chew on new leaves, but seemingly only when no other option is available

Hornwort – they will eat the soft, thin needles that occur during periods of rapid growth. They seem to ignore the thicker needles produced during slower periods of growth

Plants Scuds Don’t Seem to Eat**

Duckweed – no indication of consumption

Amazon Frogbit – no indication of consumption

Salvinia minima – no indication of consumption

Water Lettuce – no indication of consumption

Amazon Sword – only when desperately hungry and plant is weakened. The leaves and stems of a healthy plant are far too tough.

Java Fern -only when desperately hungry and plant is weakened. The leaves and stems of a healthy plant are far too tough.

Hornwort – no indication of consumption

Guppy Grass (Najas Grass) – no indication of consumption

Dwarf Hairgrass – no indication of consumption

Breeding

Freshwater amphipods have two sexes (male and female) and require both to reproduce. A mating pair can be easily identified by one appearing to “piggy back ride” on the other. They will maintain this position for a long time, and can often be seen swimming and feeding while in this arrangement. When a female’s eggs are fertilized, she will carry them around for 2 to 4 weeks until they are developed enough to be released when the mother molts. The young will spend most of their time hiding in the substrate and under other objects to avoid predators. In about 2 months the young will be old enough to begin breeding themselves. In an aquarium without predatory fish, amphipods can be seen swimming throughout the water column, looking for food and mates.

Two amphipods mating.

In the Aquarium

Amphipods make a great live food for many species of aquarium fish and amphibians including African Dwarf Frogs and Axolotl. They are busy critters that can be seen swimming across the open water or investigating nooks and crannies in the substrate for food. In aquariums with fine substrate like sand or uncapped soil, amphipods will dig just below the surface to find food and security. In the right conditions they can reproduce relatively quickly in an aquarium with little need for intervention. They prosper in heavily planted tanks with lots of places to hide from hungry fish.

Since they feed on just about anything, they sometimes will consume some plants. Most healthy plants have natural defenses against being eaten by animals like amphipods, but if the plants are already weakened from poor nutrition or water quality, they can be quickly consumed by a large colony. They key may be in keeping their numbers in check, either by manual removal or the presence of predators like small fish.

A juvenile amphipod clinging to aquarium wall.

Starting Your Own Colony for Live Fish Food

It is fairly easy to start and maintain a colony of amphipods for use as live food. I keep them in my aquariums as a sort of naturally occurring snack, but you can keep them in their own container to collect from as needed. I have written up a handy guide explaining all you need to know to get started.


* This list is based solely on my own observations. Take this information with a grain of salt and do your own research.
** This list is based solely on my own observations. Take this information with a grain of salt and do your own research. This list refers to live plants. Dead plant material is happily consumed by scuds and many other animals.

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