Japanese meagre

Where they come from

Japanese meagre, also called mulloway, are big coastal drums from Japan down through China and into Australia, plus parts of southern Africa. You find them in surf zones and estuaries, cruising sandy channels and river mouths. At night they drum with their swim bladders, which you can actually hear in a quiet room if you keep them.

Setting up their tank

• Footprint and volume: for juveniles under 40 cm, 8,000-12,000 L is a workable start. Adults need far beyond that. Long, oval, or raceway-style tanks help them cruise without smashing into corners.
• Temperature: 18-23 C. They are temperate-subtropical. A reliable chiller is as important as a heater.
• Salinity: 32-35 ppt. Juveniles tolerate brackish, but stable full marine is easiest once settled.
• Flow: steady, laminar flow they can swim against. 4-6x turnover through filtration plus extra circulation works well.
• Substrate: fine sand or bare bottom. They nose around but do not need deep beds.
• Aquascape: keep it open. Low rock ledges or a single bommie is plenty. Avoid maze-like scapes that trap a fast fish.
• Lids: tight, with netting or acrylic. They jump and they spook.

Filtration needs to be heavy-duty. Big mechanical prefilters to catch the mess, a skimmer rated way above system volume, and either a large fluidized bed or oversized biomedia. Plan on vigorous gas exchange and backup aeration. These fish suck down oxygen, especially after feeding.

• Equipment checklist:
• - Commercial-grade skimmer
• - Canister or drum filter for mechanical stage
• - Large biofilter or moving bed
• - Chiller with redundancy or alarm
• - Two air pumps on separate circuits or an oxygen cone
• - Big UV unit to keep water polished and reduce parasite load
• - Black background and minimal side reflections

What to feed them

They are greedy carnivores. New arrivals usually take live shrimp or small fish first, then you can wean them onto dead foods and finally pellets. Consistency is everything.

• Good staples:
• - High-quality marine carnivore pellets sized for big fish
• - Chopped squid, cut fish fillet, and whole silversides
• - Prawns and mussels in rotation
• - Gel diets for predators if you can get them to accept it

Feed smaller portions 2-3 times per day while they are growing, then taper to once daily for big fish. Soak frozen items in a vitamin mix a few times a week. Do not rely on oily baitfish alone or you will end up with fatty liver and messy water. I skip feeder goldfish entirely. If you use raw shrimp or smelt regularly, balance it with pellet and squid to avoid thiaminase issues.

How they behave and who they get along with

Juveniles like company and settle better in a small group if the tank is truly big. They are skittish in bright light, calm in dim light, and they drum at dusk. They are not bullies, but they are predators. Anything bite-sized is a snack. Adults get more independent and will ignore similarly large tankmates.

• Tankmate ideas for temperate or cool-marine setups:
• - Other large, even-tempered drums or croakers
• - Large, non-nippy jacks or trevallies that match the temperature
• - Rays from temperate water in truly huge systems
• Avoid: triggers, large wrasses that harass, and anything small or delicate.

Breeding tips

This is an aquaculture species, so it can be bred, but it takes giant tanks or ponds and careful control of light and temperature. Spawning adults drum, release pelagic eggs, and the larvae need live foods. It is not a home project.

• How farms do it, in broad strokes:
• - Condition a broodstock group on rich seafood and pellets
• - Ramp photoperiod and temperature to around 20-22 C
• - Induce or cue spawning in a very large, round tank
• - Collect floating eggs and hatch separately
• - Feed rotifers, then Artemia, then wean to microdiets
• - Maintain impeccable water quality throughout

Common problems to watch for

• Outgrowing the tank: plan an exit route. They do not stop getting bigger.
• Glass strikes and nose rub: reduce reflections, use rounded corners if you can, and keep lighting gentle.
• Low oxygen after big feeds: add aeration and surface agitation. Nighttime is the risky window.
• Parasites like Neobenedenia and Cryptocaryon: quarantine for 4-6 weeks. Praziquantel for flukes and a monitored copper treatment for marine ich are standard tools.
• Warm-water bacterial issues (Vibrio): keep temps in the target range, avoid big swings, and move quickly if you see red sores.
• Nutritional gaps: vary the diet and use vitamins. Too much oily fish leads to fatty liver and greasy skimmers.
• Ammonia spikes: heavy feeding will outpace filtration. Test often and clean mechanical filters before they clog.
• Jumping: tight lids and calm handling during maintenance.