Clownfish are sequential hermaphrodites - they all start as males and the dominant fish in a group becomes a female. The easiest path to a breeding pair is buying two captive-bred juveniles of any common species (Ocellaris, Percula, Onyx, Snowflake) and letting them sort it out. The larger of the two will turn female within months; the smaller stays male. Avoid mixing two known females (they will fight to the death) or buying a pair that the seller cannot confirm has actually spawned.
A 20-gallon long with a small ceramic pot or piece of slate creates the substrate clownfish prefer for laying eggs. Stable parameters (78-80F, 1.025-1.026 SG, alk 8-9 dKH) and high-quality food twice a day are the two biggest spawning triggers. Pellets and frozen mysis daily, with weekly variety like nori, Cyclop-eeze, or LRS Reef Frenzy, gets a healthy pair laying within 6-12 months. Lights on a 10-hour photoperiod with a slow ramp on either end. An anemone is helpful but not required - many captive pairs spawn on bare slate.
A typical Ocellaris pair lays 200-800 eggs per clutch, every 10-14 days. The male tends the eggs and aerates them with his fins. Eggs hatch 7-10 days after laying, almost always at night within 1-2 hours of lights-out. The morning of hatch, the eggs darken and you can see silver eyeballs. That night, harvest the larvae or move the entire substrate to a dedicated larval tank.
Newborn clownfish larvae are 2-3 mm and require live rotifers (Brachionus plicatilis) for the first 7 days of life. You need a rotifer culture going before the eggs hatch - rotifers do not appear from nothing. A 5-gallon bucket with phytoplankton, gentle aeration, and a starter culture of rotifers gets you a feeding population in 4-7 days. After day 7-10, larvae transition to baby brine shrimp (Artemia nauplii), which you also need to be hatching daily. By day 21, larvae start metamorphosing into miniature adults and accept finely crushed pellets. Survival rates for first-time breeders are typically 20-40%; experienced breeders get 70-80%.
Three failure modes account for most lost broods: not having the rotifer culture ready before hatch (larvae starve in 24 hours if there is nothing to eat), water quality crashes in the larval tank (small water volume + heavy feeding = ammonia spikes), and lighting too bright or too dim during the first week (larvae need very dim light to feed effectively). Get those three right and the rest is iteration.