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Specialized scientists have filmed and studied interactions between various species of fish and sharks in the Pacific, Indian and Atlantic oceans.
The curious reason why tuna rub against sharks
Scientists at the University of Western Australia have discovered that tuna and other large fish rub against sharks to get rid of parasites, their article published in The Conversation suggests.
Scientists have filmed and studied scratching interactions between several species of fish and sharks in the Pacific, Indian and Atlantic oceans, and found that fish preferred to rub on sharks rather than other fish, according to their research, published in PLOS One. The size of sharks also matters for fish, as fish that barked on sharks were larger than those that barked on other fish, suggesting that predation risk may be a limiting factor.
The secret of the risky ‘game with death’ is that the shark’s skin is made up of small tooth-like structures called dermal denticles.
Scientists suggest that tuna and other fish use scratching to remove parasites and dead skin. This hypothesis is supported by the fact that fish tend to scratch their heads and sides more than other parts of the body, which are the areas most affected by parasites.
Pelagic fish (those that move independently of movements of the water) are host to a wide variety of parasites, but their environment provides them with few options to eliminate them.
The number of some species of sharks has decreased by 92 % off the coast of Australia. Scientists fear that their further extinction could complicate the fight of fish against parasites around the world. Biologists have found that tuna in all of the world’s oceans tend to scratch on sharks.
Decreasing shark populations in the ocean may limit these interactions, exerting further pressure on species that are already highly vulnerable, the study concludes.
