Thompson's poacher

Where they come from

Thompson's poacher (Freemanichthys thompsoni) is one of those cold-water oddballs from the North Pacific. Think deeper, rocky areas with current, low light, and a lot of sitting-and-waiting for food to drift by. If you try to keep it like a typical reef fish, it usually goes downhill fast.

Setting up their tank

Plan around two things: cold water and a fish that wants to perch and wedge itself into structure. I kept mine in a temperate setup with a chiller and lots of rockwork, and it spent most of the day posted up like a little armored gargoyle.

• Temperature: keep it cold and steady. Aim roughly 50-60F (10-16C). Short warm spells are what usually start the slide.
• Tank size: bigger than you think for stability. I would not bother under 40 gallons, and 75+ gallons makes temperature and nutrients easier to manage.
• Aquascape: rock piles, ledges, and caves. They like hard surfaces and tight spots, not open sand flats.
• Flow: moderate, with calmer pockets. Give it a place where food can settle and it can hold position without getting blasted.
• Lighting: subdued is fine. Bright reef lighting is not doing you any favors here.
• Substrate: sand is OK, but rockwork matters more. Make sure rocks are stable and cannot shift.

Filtration-wise, think messy predator. You want strong mechanical filtration you actually clean, plus plenty of biological capacity. I also liked running carbon because some of the foods that work best for them can funk up the water if you get lazy.

What to feed them

They are built for ambush and snapping up meaty bits. Mine took frozen pretty readily once it recognized tongs as the dinner bell, but the first couple weeks can be stubborn.

• Frozen mysis (a staple once they accept it)
• Chopped krill (use smaller pieces than you think)
• Enriched brine shrimp (good for tempting, not a long-term main food)
• Chopped clam, squid, or shrimp (rinse well to keep the water cleaner)
• Small live foods as a jump-start if it will not take frozen (live mysids, live ghost shrimp acclimated to salt, or similar)

Feed smaller amounts more often at first. A new poacher that gets one big meal and then goes ignored for days can sulk and stop responding. Once it is settled, you can usually land on a steady routine (every other day or so) depending on size and tank temp.

How they behave and who they get along with

Expect a sit-and-stare fish. It is not "active" in the way most people mean, but it is super interesting up close. They perch, adjust their position, and do short bursts to grab food. Mine was bold at feeding time and invisible the rest of the day.

• Best tankmates: other temperate species with similar temperature needs and calm behavior
• Avoid: fast, aggressive feeders that will steal everything before the poacher reacts
• Avoid: anything small enough to fit in its mouth (it is still a predator)
• Use caution: nippy fish that pick at fins or harass bottom-perchers

They are generally not looking for trouble, but they will defend a favorite crevice. Give multiple perching spots and line-of-sight breaks if you are keeping more than one bottom-dweller.

Breeding tips

Breeding in home aquariums is rare and, honestly, not something most people should plan around. Spawning cues for temperate marine fish often involve seasonal temperature shifts, photoperiod changes, and a lot of live food at the right time. If you ever see courtship behavior, you are already in pretty deep with a dedicated temperate system.

Common problems to watch for

• Heat stress: the silent killer. Gasping, lethargy, hiding constantly, and loss of appetite can show up after a warm spell.
• Shipping damage and refusal to eat: they can arrive beat up or spooked. Give low light, quiet, and offer small meaty foods right on the perch.
• Starvation-by-competition: looks "fine" but slowly gets thinner because tankmates outcompete it at every feeding.
• Poor water quality from heavy meaty feeding: cloudy water, rising nitrate, and film on the surface if you overdo it or do not clean mechanical filtration.
• External parasites and bacterial issues after stress: watch for frayed fins, redness, or rapid breathing. Quarantine is your friend with a fish this sensitive.

My general rule with these: if something is off, slow down and simplify. Dim the lights, reduce activity around the tank, offer a small high-smell food (mysis or chopped clam), and check temperature and oxygenation before you do anything else.