Australian-led researchers conducing fascinating research have documented an unusual example of “helicopter parenting” performed by males and females of the spiny chromis damselfish. The findings have ramifications for the makeup of coral reef communities.
“In the marine environment the care of fish eggs is common, but caring for the tiny larval fishes after they hatch is rare,” says lead author Alexandra Grutter of the University of Queensland.
While most reef fish larva leave for the open ocean, spiny chromis damselfish larva stay on the reef where they are exposed to gnathiid isopods, parasites that gorge on the blood of a fish, like the ocean equivalent of mosquitoes.
“From our previous research we know gnathiids are especially harmful to juvenile fishes by reducing their swimming, competitiveness, escape response, aerobic performance and overall survival,” says Grutter.
In 2018, Grutter and colleagues discovered that adult spiny chromis damselfish have gnathiids in their faeces. From this and other field observations, the team hypothesized that parents protect their young by eating the parasites.
In a laboratory test of their hypothesis, the researchers repeatedly set up pairs of aquariums with damselfish offspring: one tank with a parent fish and the other without. They then added gnathiid parasites to each tank and recorded fish mortality over the course of three days.
The survival rate of the young fish with a parent was three times higher than those without a parent fish.
“Given how tiny the damselfish offspring are, these fish parents have really come to the rescue,” says Grutter.
Grutter and colleagues argue that parasites are an overlooked source of high mortality for young fish living on reefs. Given the high mortality of spiny chromis damselfish without parental care, the researchers point out that parasitism impacts the species composition of coral reef communities.
“We are now interested to learn how other young fishes without such parental care avoid suffering from gnathiid parasitic infection,” says Grutter. “We will be keen to see if there are other examples of fish showing parental care involving the consumption of parasites.”
The research is published in the journal Proceedings of the Royal Society B: Biological Sciences.
The Ultramarine project – focussing on research and innovation in our marine environments – is supported by Minderoo Foundation.