Spring bitterling

Where they come from

Spring bitterlings (Rhodeus suigensis) are small temperate cyprinids from East Asia, showing up in slow streams, ponds, and rice-field channels with clean, cool water. The key detail about their home waters: there are freshwater mussels around, because that is where they lay their eggs.

Setting up their tank

Give them room to spar and school. A 24-30 inch tank (20-30 gallons) works for a group of 8-10. They look best in a planted setup with gentle flow and plenty of open swimming space.

• Temperature: 54-72 F (12-22 C). Aim for 60-68 F (16-20 C) most of the year.
• pH and hardness: around neutral to slightly alkaline, pH 6.8-7.8, moderate hardness (5-15 dGH).
• Flow and oxygen: gentle current with good surface agitation. They appreciate well-oxygenated water.
• Filtration: something steady and mature. A sponge prefilter helps protect any fry.
• Substrate: sand or fine gravel so mussels (if you use them) can settle, and plants can root.
• Aquascape: dense plants along the back and sides, open center, some wood or stones to break sight lines.
• Lighting: moderate. They color up nicely with a planted-tank light but do not need it bright.
• Lid: use a tight lid. They jump during spats or courtship.

What to feed them

They are opportunistic omnivores. Mine perk up for moving foods and do well on a mixed diet. Small mouths, so keep particle size modest.

• Staples: quality micro-pellets and fine flake.
• Frozen/live: daphnia, cyclops, baby brine shrimp, chopped bloodworms (as a treat).
• Green stuff: they pick at biofilm and will take spirulina flakes; a touch of blanched spinach or peas now and then is fine.

How they behave and who they get along with

Peaceful, active, and a bit theatrical. Males posture and flash at each other, especially as the water warms in spring. Keep them in a group so the sparring spreads out and feels natural.

• Good tank mates: white cloud mountain minnows, medaka ricefish, small danios that like cooler water, small Corydoras from cooler habitats, Sewellia/Gastromyzon hillstream loaches (if you provide some flow and oxygen).
• Usually OK: adult Neocaridina shrimp in a well-planted tank, but babies will be snacks.
• Avoid: large or nippy fish (big barbs, most cichlids), warm-water tropicals, and anything that will outcompete them at feeding time.

Breeding tips

This is the fun, quirky part. Bitterlings lay their eggs inside live freshwater mussels. The female develops a long ovipositor in season, deposits eggs into the mussel, and the male releases milt at the mussel's siphon. The mussel broods the eggs, then spits out tiny fry.

• Seasonal cue: give them a cool winter, then let temps rise to about 64-68 F (18-20 C). Males color up and pick a mussel to guard.
• Mussels: use compatible freshwater mussels (commonly Anodonta/Unio/Sinanodonta species in the hobby). Partially bury them with the intake siphons exposed.
• Breeding tank: set up a separate, quiet tank with the mussels, plants, and a seasoned sponge filter. Move in the fish once females show ovipositors.
• Spawning: you will see the male display at the mussel and the female insert her ovipositor. This can repeat over several days.
• Fry: after 2-4 weeks, the mussel releases fry. They are tiny. Start with infusoria/green water, then switch to microworms and newly hatched brine shrimp as they size up.

Common problems to watch for

• Heat stress: they get lethargic, breathe fast, and colors wash out above the low 70s F. Add surface agitation, shade the tank, and cool the room.
• Mussel die-off: a dead mussel can nuke water quality fast. Keep them in a basket so you can check them, and remove any that stay open or smell off.
• Male aggression: cramped quarters and too few females lead to shredded fins. Add line-of-sight breaks and increase group size.
• Parasites/ich: treat early, but avoid copper with any inverts present. Salt and raised temps can help, but do not push the fish into the high 70s F.
• Skinny fish: often diet-related. Increase frequency of small, protein-rich meals and consider a broad-spectrum dewormer in a hospital tank if needed.
• Oxygen dips: hot days, too much decaying plant matter, or clogged filters can crash O2 levels. Keep filters clean and keep the surface rippling.