What are the fleas in an aquarium? - briefly
Water fleas are microscopic branchiopod crustaceans, commonly Daphnia species, that inhabit freshwater tanks. They provide a natural source of nutrition for many small fish and invertebrates.
What are the fleas in an aquarium? - in detail
Aquarium “fleas” are minute freshwater crustaceans belonging to the order Cladocera, most often represented by species of the genus Daphnia and related genera such as Moina. They are colloquially called water fleas because of their jerky swimming motion, which resembles the hopping of a flea.
These organisms measure 0.2–5 mm, possess a transparent carapace, large compound eyes, and thoracic limbs adapted for filter‑feeding. They draw suspended particles, including algae, bacteria, and detritus, through rhythmic beating of their appendages, converting them into biomass.
The life cycle includes parthenogenetic reproduction under favorable conditions, producing clutches of 10–50 neonates every 1–3 days. Sexual reproduction is triggered by crowding or environmental stress, yielding resting eggs (ephippia) that survive desiccation and extreme temperatures.
In a closed system they serve three primary functions:
- Live food source – readily consumed by fry, small fish, and invertebrate larvae.
- Biological filter – reduce suspended organic matter, helping to maintain water clarity.
- Indicator species – rapid population changes signal shifts in water quality, such as ammonia spikes or pH fluctuations.
Identification relies on visual cues: a rounded, translucent body; a single median eye; and rhythmic antennal beating. Magnification of 10–20× typically reveals the characteristic shape and movement.
Management guidelines:
- Cultivation – maintain a starter culture in a separate container with gentle aeration, feeding with infusoria or powdered algae.
- Population control – harvest excess individuals daily; avoid overfeeding to prevent blooms that deplete oxygen.
- Water parameters – keep temperature between 18–24 °C, pH 6.5–8.0, and nitrate below 20 mg/L to sustain healthy growth.
- Prevent contamination – filter incoming water through fine mesh to remove stray eggs or larvae that could introduce unwanted species.
Properly regulated, these tiny crustaceans enhance nutrient cycling, provide a reliable food chain link, and contribute to overall system stability.