Quarantining new fish isn’t only for disease prevention. Finicky eaters should be conditioned and trained to eat frozen foods in a quarantine tank. A bare bottom tank is easier to keep clean, and makes it easier for the fish to find food. Fill an appropriately-sized tupperware container with sand for burrowers. Keep lighting low and use a PVC pipe to give your fish somewhere to hide. Take a few minutes to siphon the bottom of the tank before and after each feeding. Keep the quarantine tank free from feces, uneaten food, detritus, and ammonia.
Live food eaters simply don’t recognize frozen foods as possible food items; it’s up to you to teach them. Research the fish’s natural diet and provide similar live foods until the fish has gained weight. Buy live foods before your fish arrives. HUFA-enriched live adult or newly hatched Artemia are an easy, cheap alternative to natural foods for most finicky eaters and can be substituted for live shrimp or copepods, though some copepods are easy to culture at home. Obligate Corallivores may need live coral sacrifices. Try pasting frozen mysis onto a skeleton or live coral to entice them. Attach frozen food with a rubber band to a clam shell or live clams from the grocery store for angelfish. Larger ambush predators like lionfish and anglers prefer live ghost shrimp or small fish like damsels (never goldfish). Use water movement from a pipette or a feeding stick to make frozen food “look alive.”
Make sure frozen food is as fresh as possible! Live food eaters are more likely to refuse food with an “off” taste or smell, even when it looks fine to us. HUFA and omega 3s degrade quickly in frozen food. Never use food that has been thawed and refrozen. Discoloration or freezerburn is a sure sign of bad food, like brown mysis. Don’t rely on the expiration date when feeding finicky live food eaters, as the food’s flavor and HUFA profile will change well before the expiration date. Ideally, use food that has been in your home freezer for no more than a few months. Your LFS should use a commercial freezer which keeps the food at -30C or -22F.
Garlic in the diet of marine fish is controversial, but many aquarists report an increase in appetite with garlic use. It may also help condition fish to recognize new foods when they are trained to associate garlic smell with food. Soak the fish’s preferred live foods in garlic. Once they’re accustomed to that, freeze the garlic soaked live foods and introduce that along with live food. Mix in garlic soaked store bought foods until the fish eat frozen food well. Garlic can be slowly removed from the diet once training is complete.
Be persistent. It can take months for a stubborn fish to learn to eat frozen food. Keep in mind that some fish, like dwarf seahorses, will never eat frozen foods, and some species, like mandarins and sponge eaters, may not thrive on a strictly frozen food diet.