Garden eels (subfamily Heterocongrinae) are marine creatures that populate the sandy floors of tropical oceans, often near coral reefs. They live in large colonies, with each eel anchored in a burrow and extending its upper body into the water. This behavior makes them resemble plants gently swaying in the current. Garden eels are sessile feeders, meaning they remain fixed in one place for almost their entire lives. This lifestyle dictates that their diet is entirely dependent on the flow of the ocean, which brings their sustenance directly to them.
Primary Diet in Natural Habitats
The diet of garden eels consists almost entirely of minute organisms and particles suspended in the water column. As continuous, opportunistic feeders, they rely on a constant trickle of planktonic food. Zooplankton forms the bulk of their nutrition, including tiny animals like copepods.
Their diet also includes micro-crustaceans, various crab and shrimp larvae, and small fish eggs that drift past their burrows. The size of the food particle is critical: items smaller than 0.3 millimeters or larger than 2 millimeters are often ignored. This means they are adapted to consuming a narrow range of suspended matter delivered by the current.
Microscopic plants (phytoplankton) and suspended particulate matter also contribute to the eels’ caloric intake. Since they never leave their burrows, the density and composition of the plankton-rich currents determine their nutritional well-being. A high flow of nutrient-rich water is important for the survival of a garden eel colony.
The Passive Feeding Strategy
Garden eels employ a passive strategy that maximizes feeding efficiency while minimizing energy expenditure. Anchored firmly within their mucus-lined burrows, they extend up to one-third of their bodies into the open water. Every eel in a colony typically faces the same direction, positioning themselves to intercept food carried by the prevailing current.
The feeding action involves the eel snapping at a passing food particle. They rely on excellent vision to spot minuscule prey drifting within a short distance of their mouth. This short-range snatching allows them to consume the constant stream of plankton, with strike rates sometimes exceeding one hundred bites per minute when prey density is high.
When currents become stronger, garden eels adjust their feeding posture to conserve energy. They retreat slightly further into their burrows and adopt a curved body shape, which reduces drag. This behavioral adjustment allows them to continue feeding across a wider range of flow speeds by focusing their strikes on only the closest zooplankton.
Maintaining Garden Eels in Captivity
The passive feeding behavior of garden eels presents challenges when maintaining them in aquariums. Since they require a continuous, drifting supply of food, they cannot be fed like most other fish. They need multiple micro-feedings to replicate the natural flow of plankton.
Aquariums must use specialized live and prepared foods broadcast into the current to mimic their diet. Common foods include enriched live copepods, rotifers, and brine shrimp, which are small enough to drift naturally. Finely blended food slurries, such as mysis shrimp or oyster eggs, are also used, often dispensed via automated dosing systems.
The food must be delivered using a gentle but consistent water current, ensuring particles drift past the eels’ heads. Traditional methods, such as target-feeding, are ineffective because the eels ignore food that does not drift naturally with the flow. Success hinges on providing a continuous supply of appropriately sized food that simulates plankton-rich currents.