A large emperor cichlid hovers over its clutch of eggs on the sandy bottom of Lake Tanganyika. A scuba diver glides close. The moment the diver’s eyes fix directly on the eggs, the fish flares its gill covers and charges. The same diver turns its head away or spins around, and the attacks drop sharply.
Emperor cichlids (Boulengerochromis microlepis) attacked divers significantly more often when divers looked directly at the eggs or fry than when they averted their gaze or turned their fins toward the clutch, researchers report in Royal Society Open Science. The attack rate matched what happened when divers stared straight at the guarding parents themselves.
Gaze is a pivotal signal in animal societies, shaping not only predator avoidance but also social interaction, the team writes in the paper. Yet studies of how fish read gaze have lagged behind work on mammals and birds. Shun Satoh and colleagues wondered whether these giant African cichlids — some of the largest in the family, reaching 80 centimetres — could tell where a diver’s attention was aimed.
The researchers tested breeding pairs guarding either eggs or newly hatched fry that still huddled motionless in a sand hollow. They positioned a diver 30 centimetres from the clutch and ran four 60-second trials in random order. In one, the diver gazed straight at the offspring. In another, the diver kept the same distance but looked away. In the third, the diver turned completely around yet kept the fin tips pointing at the clutch. In the last arrangement, the diver stared at the guarding parent instead.
From underwater video, the team counted aggressive charges — body turned toward the diver plus flared gill covers — and measured how long each fish stayed within roughly its own head length of the diver.
Male fish attacked more than females overall. But the pattern was clear: fish struck far more in the “gaze at offspring” condition than when the diver looked away or turned its back with fins toward the clutch. Aggression stayed just as high when the diver eyed the parent. Fish also tended to linger closer to the diver when its fins pointed at the clutch, even if the face looked elsewhere.
These findings suggest that fish may possess a rudimentary form of “attentional attention” — the ability to recognize where another individual’s focus lies, the authors conclude. The result surprised even the team because fish eyes and bodies usually point the same way, making it hard to tease apart gaze from simple orientation. Yet the emperor cichlids reacted differently when the diver’s eyes targeted the vulnerable offspring versus when the body simply faced that direction.
The researchers note that emperor cichlids give extended parental care for up to nine months and breed only a few times in a lifetime. Most of the fish tested had probably never encountered divers while guarding young, so a simple learned fear of masks or bubbles could not easily explain the fine-tuned response.
The ability of emperor cichlids to modulate their responses according to a diver’s attentional state highlights that gaze sensitivity is an ecologically relevant trait in vertebrates, the paper states. The authors caution that more work is needed to rule out simpler explanations, such as reactions to looming shapes or body angle alone. Still, they say the controlled design and the fish’s life history make Pavlovian conditioning unlikely.
Because scuba diving is growing as ecotourism, the team points out that even a diver’s gaze — not aimed at the fish — can alter behaviour and perhaps raise stress. “Stress triggered by diver gaze could, in turn, influence key fitness components, including reproductive success,” they write.
Citations
S. Satoh et al. Watching the watchers: emperor cichlids can perceive attention towards their offspring by divers. Royal Society Open Science. Published online March 18, 2026. DOI: 10.1098/rsos.251919
