The hangers-on

archive – Marine LifeThe hangers-on

Suckerfish have nasty habits, agrees JAMIE WATTS – but look closer and divers can appreciate their redeeming features. They can be good for a laugh too, when they latch on to unsuspecting buddies, such as photographer MALCOLM NOBBS

IN SEPTEMBER 2013, Malcolm was enjoying a dive at Osprey Reef in Australia’s Coral Sea when his buddy Mick Todd suddenly developed what appeared to be an inappropriate interest in Malcolm’s rear end.
Even more of a worry was when Mick started photographing Malcolm’s butt. Surely he wasn’t narked?
Back on board, he showed around his photograph of a remora latching firmly onto Malcolm’s bum.
At first glance remora are pretty repulsive. Sharksuckers, whalesuckers, turtlesuckers, even marlinsuckers – sucking onto a host’s skin just seems horrible, parasitic, leech-like. The slatted, sharp-ridged oval sucker on top of the head looks unpleasant, too.
Then there are the huge staring eyes and that confusing lower jaw, longer than the upper jaw, so that the animal appears upside-down. Remoras have the habit of moving around the host sideways, and don’t seem to worry too much about which way is up – sometimes they really are upside-down.
Everything that travels through the oceans is superbly streamlined, and even if you don’t call a remora a parasite (and you can argue either way) it definitely causes drag.
If you try to pull one off a moving host the ridges on the suckers dig in, and can cut into the skin. Using remoras as “manta handlebars” is beyond impolite.
The sucker is a modification of the dorsal fin, basically the spines split off to either side, then flattened into slats and formed into a pad. The suction has been reportedly used in turtle “fishing”, with a remora on a leash thrown in to attach to a turtle, which is then hauled in.
Remoras have nasty eating habits too, with faeces and sloughed-off, dead or damaged skin all on the menu.
Ecologically this makes sense – allow the big, efficiently moving forager to gather food, then make use of the wasted calories. It may be elegant but physically it’s unappealing.
I’ve seen several divers receive amusing unwanted attention, too, usually in the crotch or bum area, as from an excessively persistent leg-humping terrier.
So is there anything redeeming about these grotty little creatures? Well, yes (of course!). Dietary studies have revealed remoras’ preference for parasitic copepods, which are particularly nasty little monsters that bury deep into the skin of large animals and suck and chew their blood, blubber and skin.
The remoras probably clear off many of the more unpleasant burrowing barnacles before they get a good hold on their host, too, and may see off nastier nasties such as lampreys and cookie-cutter sharks. Add to this cleaning dead skin off wounds, and remoras are sounding rather more like on-board cleaner-fish and skin-minders.

IT GETS BETTER. Small and young remoras travel inside gills or mouths. Gill parasites are a constant drain on all fish, so the remoras perform a valuable service here from an early age.
I am not aware of any studies verifying this, but I like the idea of a remora living with its host – a cute pet toothbrush with which you grow up. And when you look at them in a different light, they could almost be cute.
Diving off Bali, I felt something soft nudge my thigh. I whirled around instinctively and scared off a foot-long sharksucker. Its wide eyes and pouting lower lip managed to convey hurt at my reaction, and it skulked off to join two others.
There was no host in the vicinity, and I followed them for a while. They swim rather well and elegantly, and they were describing slow, meandering circles, picking out tiny zooplankton swarming visibly off the black-sand slope.
Many suckers spend quite significant parts of their lives free-swimming, picking out plankton.
One of these three was significantly smaller than the others, and started paralleling its larger cousin, sliding underneath to slipstream and then try to latch on with its headgear for a ride. The bigger fish shook it off, once again with that look of shock and outrage.
There are eight species of sharksucker, including two species of Echeneis sharksuckers, slender fish with a dark stripe running from the snout through the eye to the tail, and the five species of stockier, more muted-patterned, pale grey/brown remoras (genus Remora).
The remora species have clear preferences for specific hosts. Two prefer marlins and other billfish; one attaches to mantas and one prefers whales, with the largest member of the genus a generalist on large animals.
The eighth species in the family is the small, rare slender sharksucker, which spends much of its time free-living.

Appeared in DIVER October 2016


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