Richard Collins: What zebrafish can tell us about lockdown

“SOCIALISING is good for people’s mental health and wellbeing,” say Hande Tunbak and Mireya Vazquez-Prada of University College London. Prolonged isolation, they claim, can damage your health and, paradoxically, “loneliness often results in even lower desire for social contact, leading to further isolation”.

Some quite normal people, however, prefer to be alone and avoid social interaction wherever possible. The Scottish sailor Alexander Selkirk, who spent over four years alone on an island in the Pacific, showed no ill-effects afterwards.

In many religious traditions, isolation in the wilderness is deemed good for soul and body. The consequences of cocooning during lockdown, however, seem to suggest otherwise. Anxiety and depression, by all accounts, are rife just now. Will victims recover when lockdown ends? Are the adverse effects of prolonged isolation reversible? Can animal research throw any light on these pressing questions?

The usual research assistants, fruit flies and mice, have little to offer scientists this time around, but help may come from an unlikely source — a fish.

Zebrafish are native to the warm freshwaters of South East Asia. Members of the minnow family, 3cm to 4cm long, they are popular with aquarium owners. I kept zebras for years myself. They move about in shoals and most baby fish soon join their siblings in shoals. But some youngsters don’t. One in 10 zebrafish chooses to become a lifelong ‘loner’. In this respect, their communities resemble human ones. The bodies of juvenile zebras are transparent, making it easier for scientists to monitor a fish’s brain activity.

Tunbak and Vazquez-Prada decided that studying the ways of zebrafish might help answer questions about social isolation. They began by comparing brain activity in social and anti-social zebras. There proved to be significant differences in neural activity between the two. Next, they removed some social fish from their shoals and placed them in isolation for two days. The brain activity of the fish changed during this solitary confinement; areas associated with stress and anxiety were activated. Isolation led to “profound disruption of neural activity in brain areas linked to social behaviour, social cue processing and anxiety/stress”. However, isolation did not change a fish’s innate disposition; the socially isolated fish did not become ‘loners’.

When the temporarily isolated fish were returned to their shoals, they seemed to have difficulty reintegrating. However, they did resume normal social life when given anxiety-reducing drugs. How do these findings relate to humans forced into lockdown? The experiment, the researchers conclude, “provides a glimpse into how human behaviour could be affected by lengthy periods in isolation”. Fish display “an increase in anxiety resulting from hyper-sensitization to social stimuli, similar to the effects of isolation on humans”. The results suggest that “humans could feel anxious upon returning to normal life after spending a long time alone”.

Whether these research findings are relevant to the human situation or not, it is clear that zebrafish, easy to keep in captivity, provide “a powerful new tool for studying the impact of loneliness (isolation) on brain function and exploring different strategies for reducing, or even reversing, its harm”.

• Hande Tunbak et al., ‘Whole-brain mapping of socially isolated zebrafish reveals that lonely fish are not loners’. eLife, 2020.