A Practical Guide to Acclimating Moorish Idols & White Bannerfish

The Moorish Idol (Zanclus cornutus): The High-Risk, High-Reward Specialist. This is the "banner fish" of the marine aquarium hobby for a reason. Sourced from vast distance, the journey to your store is incredibly long and stressful. Idols are notoriously prone to shipping-related ailments, often refuse to eat in captivity, and have a high susceptibility to protozoan parasites like Cryptocaryon irritans (Marine Ich) and the aggressive Uronema marinum. An Idol is not a fish for a quick flip; it is a project animal that, when properly conditioned, becomes a stunning and profitable showcase specimen. 

The White Bannerfish (Heniochus acuminatus): The "Poor Man's Idol" and Your Reliable Staple. Often confused with the Idol by hobbyists, the Bannerfish is a retailer's dream by comparison. It is significantly hardier, ships with much lower mortality, and is typically an eager and undemanding eater. This is the perfect fish to offer customers who love the Idol's shape and pattern but are not equipped for its expert-level care. While generally peaceful, they are "reef-safe with caution," as they may occasionally nip at fleshy LPS corals or clam mantles.  

A clean, fish-only 5-gallon bucket. 

A length of standard airline tubing with a drip acclimation valve (or a simple knot to control flow). 

An ammonia-neutralizing water conditioner (e.g., Seachem Prime). 

Your calibrated refractometer and a thermometer. 

: Stabilize and Observe. Keep the QT lights off or very dim. The only goal this week is to make the fish feel secure and to begin offering food. Do not medicate. Watch closely for: 

Respiration: Rapid gilling is a sign of stress or disease. 

Behavior: Is it hiding motionless, or exploring its new environment? Is it scratching against surfaces ("flashing")? 

Appearance: Look for clamped fins, cloudy eyes, visible spots, or any redness or erosion on the body. 

Weeks 2-4: The Feeding Response and Targeted Action. This is where your patience pays dividends. 

Inducing a Feeding Response: This is the make-or-break challenge with Moorish Idols. Start by offering tempting live foods like enriched brine shrimp or blackworms. Once the fish is eating, begin transitioning to high-quality frozen preparations. We have seen outstanding results with LiveAquaria brand frozen mysis shrimp and their nutrient-rich LRS blends, which are highly palatable and often trigger a strong feeding response in even the most stubborn specimens. 

Taking Targeted Action: If, and only if, you observe specific symptoms, you should act.  

For Internal Issues: If you notice stringy, white feces or a fish that is eating but remains thin (classic signs of internal flagellates or worms), an in-tank medication can be stressful. This is the ideal scenario for a targeted feed. Once the fish is eating reliably, begin a course of Tropical Fish International's Health-Guard Medicated Feed. This delivers medication directly to the fish, addressing internal issues without fouling the water or adding unnecessary stress. 

For External Parasites: If you confirm the presence of white spots (Cryptocaryon) or a gold dust (Amyloodinium), then treatment is necessary. A therapeutic level of copper is the industry standard, but it must be used with care. Follow the manufacturer's instructions precisely and verify the concentration daily with a reliable copper test kit.