Hyalella azteca
Scud
Scientific Classification
Kingdom:Animalia
Phylum:Arthropoda
Class:Malacostraca
Order:Amphipoda
Family:Hyalellidae
Genus:Hyalella
Species:azteca
IUCN Status:Not Evaluated
Quick Stats
Difficulty
Easy
Environment
Freshwater
Temperature
18°C - 28°C
pH Level
6 - 8.5
Water Hardness
36 - 180 ppm
Lifespan
1 years
Origin
North America
Adult Size
1 - 1 cm
Diet
Detritivore
Creature Type
Crustacean
TDS
200 ppm
Water Flow
Low Flow
Aquarium Building Information
Minimum Tank Size
5L
Swimming Zone
middle, bottom
Oxygen Consumption
Very Low
Waste Production
Very Low
Metabolism Rate
Low
Activity Level
Active
Feeding Frequency
Daily
Food Types
Detritus
Algae
Vegetables
Flakes
Pellets
Frozen Food
Live Food
About This Species
Basic Description
Scuds, also known as Aztec Amphipods or Sideswimmers, are tiny, shrimp-like creatures that are fantastic additions to a freshwater aquarium, especially for beginners. They are incredibly hardy and don't require any special equipment like heaters, as they are comfortable in a wide range of room temperatures. Their main role in a tank is as a natural 'clean-up crew.' They are detritivores, meaning they scavenge the bottom of the tank, eating leftover fish food, decaying plant matter, and algae, helping to keep the aquarium clean. Because they are so small, usually less than a centimeter long, they can be kept in very small tanks or even a simple jar on a windowsill. They are completely peaceful and won't harm any other tank inhabitants, including snails or shrimp. In fact, many fish love to eat them, making Scuds a great source of live, nutritious food that encourages natural hunting behaviors. They reproduce very quickly on their own without any help, so a small starting group can soon turn into a self-sustaining population. Their constant activity, zipping and crawling through plants and substrate, adds a unique and lively element to the bottom levels of an aquarium.
Detailed Description
Hyalella azteca, commonly known as the Scud, is a highly adaptable and prolific amphipod that serves multiple beneficial roles in the freshwater aquarium hobby. Its value extends beyond its simple care requirements. For aquarists, they are the ultimate janitorial staff. Their detritivorous diet means they actively consume mulm, fish waste, biofilm, and uneaten food, directly contributing to nutrient export and a cleaner substrate. Unlike many other invertebrates, their diet can include nuisance algae and decaying plant leaves, further enhancing their utility. To cultivate a thriving population, a dedicated low-flow setup is ideal. A sponge filter is perfect as it provides immense surface area for biofilm growth—a primary food source—without creating a current strong enough to displace them. The tank environment should be rich with hiding places; Java moss, guppy grass, cholla wood, and a substrate of leaf litter not only provide security but also serve as continuous food sources as they decay. While they will eat standard aquarium foods like flakes and pellets, their populations boom when fed blanched vegetables (zucchini, spinach) or high-protein foods, which is useful when culturing them as live food. Their breeding is remarkably straightforward. As crustaceans, they carry their eggs in a brood pouch, releasing fully formed juveniles. This means a colony can be established from just a few individuals and will become self-sustaining. In a community tank, their population is often naturally controlled by fish predation. For this reason, they are an excellent 'on-site' food source for micropredators like Betta fish, gouramis, and various tetras, providing enrichment and a diet closer to what they would find in nature. Due to their minimal bioload and very low oxygen needs, a dense population can be maintained without significant impact on water quality, making them an efficient and low-maintenance organism for both nutrient cycling and live food production.
Scientific Description
Hyalella azteca is a freshwater amphipod crustacean belonging to the family Hyalellidae, widely distributed across North America. Its morphology is characterized by a laterally compressed body (compressiform), which facilitates its distinctive 'sideswimming' locomotion through benthic environments. As a member of the class Malacostraca, it possesses a segmented body, including a cephalothorax, a pereon (thorax), and a pleon (abdomen), with specialized appendages for locomotion, feeding, and respiration. Ecologically, H. azteca is a foundational species. It functions as a primary decomposer and detritivore, playing a critical role in nutrient cycling by processing organic detritus, consuming biofilm, and grazing on algae and macrophytes. This positions it as a key link between primary production/decomposition and higher trophic levels, serving as a vital food source for a vast array of aquatic insects, macroinvertebrates, and fish. Its physiological hardiness is notable; the species exhibits a remarkable tolerance to a broad spectrum of pH and water hardness levels, allowing it to colonize diverse freshwater habitats. Its metabolism is relatively low, and it has an exceptionally low oxygen requirement, enabling it to thrive in hypoxic zones such as the sediment-water interface or within dense aquatic vegetation. Reproduction is direct, with females brooding eggs in a ventral marsupium and releasing fully developed, miniature adults. This reproductive strategy, combined with a short lifespan of approximately one year, facilitates rapid population turnover and high productivity. Because of its ecological importance, ease of culture, and known sensitivity to various toxicants (despite its general hardiness), Hyalella azteca has become a standard model organism in ecotoxicology. It is extensively used in laboratory and in-situ bioassays to assess sediment and water quality, and to determine the sublethal or lethal effects of environmental contaminants.