Salford’s Dr Stefano Mariani and colleagues from University College Dublin and the University of East Anglia inspected stocks of striped sea bream in the Mediterranean and found that those caught near a Spanish area protected from fishing were much less impacted by the infection Ceratothoa italica than those from heavily fished areas in Italy.
Almost half (47%) of the fish from the non-protected area were infected with the parasite, compared with 30% from waters close to areas where fishing is banned.
More importantly, the researchers found that while the parasite infection significantly stunted growth and condition in the Italian fish, it had no detectable effects on the physiology of the Spanish ones.
Affectionately named ‘Betty’ by the team’s PhD graduate Maria Sala-Bozano, Ceratothoa italica breeds by swimming between fish as a juvenile and entering the mouth through the gills. A female parasite will then take up position on the tongue, virtually replacing it, and feeding on blood as it grows to adulthood.
Though the parasite poses no risk to humans, it does reduce size and life-expectancy in the fish.
The researchers came to their conclusions after establishing that the fish in the two Mediterranean areas were subject to very similar environmental conditions and the populations of both fish and parasites were very closely related genetically.
However, with the Spanish area better protected from overfishing than the Italian, the report suggests this is a major factor in the spread of virulence of the parasite.
Dr Stefano Mariani from the School of Environment & Life Sciences said: “This is further evidence that human over-exploitation of fish stocks has adverse and far-reaching effects. Areas with poor regulation have smaller, younger fish and, as we’ve now demonstrated, higher and more harmful parasite infestations.
“Betty is quite gruesome and does remind you of the Alien films, but it’s a highly adapted and specialised animal which is very successful. Unfortunately, over-fishing upsets the balance of parasite and host and interferes with the whole eco-system.
“It makes a lot of sense for protected areas to be established so we can safeguard both the quantity and the quality of the fish we eat.”
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The report has been published in the Biological Journal of the Linnean Society. You can read it here.
Photos are by Maria Sala-Bozano