The build-up: color, condition and display
Courtship starts days before spawning, and it starts with appearance. Males of most egg-laying species intensify — reds deepen, stripes darken, fins lengthen their display — while females grow visibly rounder as eggs ripen inside them. Behavior shifts with it: a male displays side-on with fins fully spread, quivers in front of a chosen female, and begins following her persistently while driving other males off. In schooling egg scatterers such as barbs and danios, look for the tempo of the whole group rising in the early morning, with males chasing females through the plants in short, bright bursts rather than the relaxed drift of the rest of the day.
Site work: cleaning, digging and guarding
Substrate-spawning egg layers — many cichlids, some catfish and killifish among them — must prepare a nursery, and the preparation is unmistakable once you know it. A pair claims a flat stone, a slate, a broad leaf or the wall of a cave and cleans it obsessively, mouthing the surface again and again. Digging a shallow pit in the gravel, moving small stones and jointly defending one corner against all comers belong to the same picture. Two fish who were tank mates yesterday and are today a united government holding one square foot of tank are a pair about to spawn. Bubble-nesting species such as gouramis show the equivalent at the surface: the male builds and tends a raft of bubbles under a leaf and courts beneath it.
The spawn itself and the hours after
The act is quieter than the courtship. Egg scatterers press together among fine-leaved plants or over a spawning mop, quivering as eggs and milt release in small batches over an hour or more, often at first light. Site spawners move in slow circles over their cleaned surface, the female laying a row of eggs, the male following to fertilize them, for dozens of passes. Afterwards the signs flip from courtship to custody: one or both parents hover over the spot fanning the eggs with their fins, refuse to leave even for food, and attack fingers and tank mates alike. Scatterers show no custody at all — and will eat their own eggs, so eggs left in a community tank simply vanish.
Recording what you saw, and deciding what happens next
Write down the pair, the site and the behavior sequence while it is fresh: a real log separates true spawning from look-alike squabbles when you review it later, and it times everything that follows, from expected hatching to when fry need their own food and space. Then decide deliberately whether this spawn is one you are raising. If it is, prepare a fry-safe tank or a breeding trap and line up homes for the young before they are free-swimming — egg layers can produce hundreds of offspring, and they become your responsibility at the same moment they become charming. If it is not, let a community spawn run its natural course without guilt.
Knowing the line between courtship and harm
Courtship carries controlled aggression, but it should never produce damage. A female with torn fins, scales missing or exhaustion from being chased without rest, or a partner battering a fish that is trying to surrender the site, has crossed into injury — separate the pair, give the chased fish cover and quiet, and if wounds look white-edged, fuzzy or inflamed, or the fish stops feeding, contact an aquatics-savvy veterinarian for advice. Keep those observations with the spawn notes in KinsLe's Pet Passport, and the pair's whole breeding history — courtships, spawns, separations and outcomes — sits in one packet, ready for the vet or for the keeper who takes your fry.