Gunther's karanteen

Where they come from

Gunther's karanteen (Crenidens macracanthus) shows up around the western Indian Ocean and Red Sea region. Think rocky coastal zones, rubble, and reef edges where there is current and lots of little crustaceans to pick off. They are not a dainty coral-reef show fish - they are built for grabbing and crunching.

Setting up their tank

Give them a marine tank that is already settled and boringly stable. These guys react badly to swinging salinity, messy sandstorms, and new-tank uglies. I would not add one to a tank that has not been running smooth for a few months.

They like structure. Build rockwork with caves and shaded breaks so the fish can duck in and out, plus open lanes for cruising. If they feel exposed, they get jumpy and skittish, and that is when they smash their mouths on rock or go off food.

• Tank size: bigger than you think - aim for a tank with real swimming length, not just volume
• Aquascape: rock piles with tight retreats plus open sand/rock flats
• Flow: moderate to strong, but avoid blasting them directly
• Filtration: strong export (skimmer helps a lot) because you will feed meaty foods
• Lid: tight-fitting cover - they can bolt

What to feed them

They are carnivores with a strong preference for crunchy, marine-based foods. Newly imported fish often ignore flakes and soft mush. The fastest way I have gotten them eating is offering small pieces of shrimp, clam, or squid on feeding tongs, then transitioning to frozen once they understand the routine.

Once they are settled, you can vary the menu a lot, but the theme is the same: high-quality marine meaty foods, not freshwater feeder stuff. They will beg like a puppy, so you have to be the adult in the room and not overdo it.

• Good staples: chopped shrimp, clam, mussel, squid, marine fish flesh (sparingly)
• Frozen options: mysis, krill (small pieces), mixed marine blends
• Useful add-ons: vitamin/omega soak 1-2x per week if the fish is new or picky
• Feeding rhythm: smaller portions more often beats one huge dump

How they behave and who they get along with

They are alert, somewhat wary fish that can flip into pushy mode once established. Expect a predator mindset: if it fits, it might get tested. They also have that "spiky, armored" vibe and are not afraid to hold their ground in a rocky corner.

Tankmates should be sized appropriately and not overly delicate. Fast, midwater fish can work if the tank is big enough. Slow, shy fish tend to get bullied or outcompeted at feeding time.

• Generally OK: robust wrasses, larger damsels, sturdy rabbitfish, similar-sized hardy reef fish (in big systems)
• Risky: tiny gobies/blennies, ornamental shrimp and small crabs, slow hoverers, long-finned "easy target" fish
• Inverts: assume shrimp and small crabs are snacks unless proven otherwise

Breeding tips

Breeding in home aquariums is not something you see often with this species. In the wild they are likely substrate spawners like a lot of coastal marine fish, but getting a compatible pair, dialing in seasonal cues, and then raising tiny marine larvae is the real mountain here.

If you ever do get two that settle and tolerate each other, the best you can do is give them space, stable conditions, and lots of food variety. Watch for paired cruising and territory guarding. If eggs show up on rock, expect the parents to get defensive.

Common problems to watch for

The big one is the slow decline after purchase: the fish looks fine, then stops eating, then you notice ragged fins or heavy breathing. That pattern usually traces back to stress plus unstable water, followed by parasites or bacterial issues taking advantage.

• Refusing food: often stress, bullying, or too much activity around the tank
• Scratching/flashing: external parasites are common on wild-caught fish
• Fast breathing: gill irritation from parasites, ammonia/nitrite spikes, or low oxygen
• Mouth injuries: bolting into rockwork or glass when spooked
• Bloat/constipation: from big meals of rich food - feed smaller portions

One last practical thing: keep a close eye on who gets to the food. If you have aggressive eaters (tangs, big wrasses), use tongs to target-feed the karanteen and spread food across the tank. A fish that misses meals in week one is the fish you will be treating in week three.