Researchers have identified a rare instance of exemplary parental behaviour in fish, specifically within a common coral reef species that actively safeguards its young by consuming parasites.
Dr. Alexandra Grutter from the University of Queensland noted that the research team observed a species of damselfish that not only nurtures its offspring but also enhances their survival prospects by feeding on parasitic gnathiid isopods. “In the marine environment, the care of fish eggs is common, but caring for the tiny larval fishes after they hatch is rare,” Dr. Grutter explained. “In most cases the larvae leave the reef for the open ocean.”
However, the spiny chromis damselfish, found in the western Pacific Ocean, uniquely retains its offspring within the reef, where both parents provide care. The study revealed that the parent fish actively consume gnathiids, which are prevalent reef parasites that briefly feed on the blood of their hosts before departing, akin to the behaviour 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,” Dr. Grutter stated. “So, this is a fascinating example of great fish parenting.”
The investigation involved introducing cultured parasites into two aquariums containing juvenile fish—one with a parent fish and the other without—and monitoring the outcomes over a three-day period. The survival rate of juvenile fish in the presence of a parent was found to be three times greater than that of those without parental care. Further laboratory and oceanic tests confirmed that the parent fish were actively consuming gnathiids for defensive purposes.
The findings are documented in the journal Proceedings of the Royal Society B: Biological Sciences. “We are now interested to learn how other young fishes without such parental care avoid suffering from gnathiid parasitic infection,” Dr. Grutter remarked. While “cleaner fish” often provide parasite-removal services, they typically favour larger fish as hosts. “Given how tiny the damselfish offspring are, these fish parents have really come to the rescue,” Dr. Grutter said.
“We will be keen to see if there are other examples of fish showing parental care involving the consumption of parasites.”
[image: A spiny chromis damselfish and its brood. Credit: Mark I McCormick]
