A guppy tank in motion can look alarming to a new keeper, because pursuit is the species' main social language. Males chase to display their colors at a flattering angle, to court females, and to remind other males of their rank. The question is never whether chasing happens; it is whether one fish is paying for it with its health.
What Normal Chasing Looks Like
In a settled group, chases are brief and rotating. A male darts after a female, she outswims or ignores him, and attention shifts within seconds. Males flare and posture at each other, then both return to feeding. Every fish eats at the surface, rests in the open at times, and carries full, intact fins. Females get breathing room between approaches, and no single fish spends its day in flight. That lively, untargeted pattern can run for much of the day without harming anyone.
Sex balance shapes the tempo. A tank with many males and few females concentrates courtship onto too few targets, so each female is pursued almost without pause. Keeping noticeably more females than males spreads the attention and lowers the temperature of the whole tank.
The Bullying Threshold
Chasing has crossed into bullying when four signs line up: one fish is chased relentlessly rather than in passing, that fish hides for long stretches, it has stopped feeding, and its fins are shredded. Treat that set as the line, stated the same way every time, because single signs mislead: a shy fish may hide without being targeted, and a torn fin can come from one nip. Together, that full set means the victim is living under constant pressure, and stress at that level opens the door to illness.
Check fins in good light, and compare the victim's feeding honestly against a week ago. If the set is complete, do not wait for the tank to sort itself out; targeted fish rarely recover rank while the aggressor stays.
New arrivals reset the chasing for a day or two. A fresh male is tested by residents, and a fresh female draws a crowd of suitors, so judge the tank only after the newcomer has learned the cover and the others have mapped the new presence. Persistent focus on that one fish beyond the settling period is different from first-day curiosity, especially when the newcomer stops exploring the whole tank and lives inside a single plant, eating only when the crowd is elsewhere.
Fixes, in the Order to Try Them
Rebalance the sexes first if males heavily outnumber females. Then break the sightlines: tall plants, floating cover, and ornaments that let a chased fish vanish from view end pursuits that open water allows to run the full length of the tank. Feed in two spots so the victim eats without crossing the aggressor's ground. If one male remains relentless after those changes, remove him to another tank or return him; keeping a single relentless aggressor costs the victim its fins, its feeding, and eventually its life.
Someone has to watch for the threshold on purpose. Care Teams builds that watch in KinsLe: one person feeds and notes whether every fish eats, one person checks fins and hiding at the evening lights, and one person owns acting on a completed threshold set, from adding cover to separating the aggressor. Duties carry names, so the observations happen daily instead of when someone happens to linger at the glass. Logged nightly in KinsLe's Care Teams, shredded fins stop being an argument about impressions and become a dated pattern someone must act on.