Sandy Hook - A Parasite for Priontus? - Underwater Naturalist: Vol. 22, Number 1: November 1993
A Parasite for Prionotus?
by DAVE GRANT

Sea robins (Prionotus) are one of the best known, but least appreciated fishes of the Middle-Atlantic waters, even though they are often the first saltwater trophy most of us catch. Although they are considered bait-stealers and trash fishes, the much maligned sea robins are perhaps the most interesting and beautiful of all our local fishes. To catch one, simply go fluke fishing with me in the summer.

Two species are regularly found in our area during the warmer months, the northern or common sea robin (Prionotus carolinus) and the striped sea robin (P. evolans). In spite of the name, the striped is the more common in Sandy Hook Bay. Also it is the larger and more attractive of the two, displaying many shades of red and orange on its body and fins as well as dashes of turquoise around the fins.

Fishermen have been known to call the adult striped sea robins, "cock robins," mistaking them for the males of the species. The smaller less colorful cousins, the northern sea robins, are assumed to be the females.

Another nickname for the sea robin is "green eye," and it may have the most beautiful eyes of any fish. It has been described as an "opalescent gem set in a ring of gold." The color can vary from rich green to dark blue to black depending on the light that strikes it.

During the 60's, U.S. Fish and Wildlife yearly creel surveys showed individual Mid-Atlantic anglers caught between 16 and 68 sea robins each summer. Some fishermen will tell you they catch that many on one fluke fishing trip.

Sea robins are the only local fish that "walk." If you are lucky enough to witness their underwater antics, you'll discover that they use their unique, detached, finger-like fin rays to feel their way across the bottom. They also use these fins to burrow into the sediments so only their eyes and the tops of their heads are exposed, a tactic for avoiding predators, to ambush prey, or to wait out the tidal currents. The fins are used as well to agitate the bottom and help sense food in the area.

Sea robins are noisy fish which is why the early European settlers called them "gurnard," a word derived from the French word grogner which means to grunt, growl, or grumble. Sea robins do all three when they are hauled out of the water on the end of a hook, much to the delight of novice anglers.

All things considered life is probably not too tough for sea robins. They are edible but are not sought after commercially on a large scale, and they certainly aren't coveted by recreational fishermen. They are omnivorous, bite on any bait, and always seem to have a belly full of anything they can fit in their substantial mouths, even unwary young sea robins. In fact examining their stomachs will provide an excellent sample of the fish diversity in the bay. Although they are the most abundant bottom fish and many are hooked every summer, most are released. Their bony heads and sharp spines probably deter lots of other creatures besides humans from eating them.

While carefully unhooking a large sea robin recently, I noticed curious, scalelike bumps on its head. At first I thought they were just another feature on the bony, heavily sutured skull, but when I touched one with forceps, it moved like an inch worm. I collected a few of these specimens and it wasn't long before I noticed that about eight out of ten sea robins I caught had them.

Most fish carry a half dozen or so and they congregate around the top of the head and between the sea robin's beautiful green eyes, above the area that is covered if the fish is buried in the sediment. The sea robin's intricately textured head offers innumerable footholds for hitchhikers.

A magnifying lens revealed the bumps to be amphipods, small crustaceans with laterally compressed bodies. They are ubiquitous in the sea, estuaries, and fresh water, and there are even a few terrestrial species. The narrow shapes, antennae, and large eyes of these tiny hitchhikers readily identified them as amphipods. Determining which species they might be and what they were doing on sea robins required a bit of study.

Most of the 600 or so species of amphipods are free-living on the bottom or in the water column. However, some live intimately as commensals or even parasites with a wide range of other creatures. Many of these arrangements are species-specific and amphipod hosts include kelp (where they are responsible for gall formation), sponges, jellyfish, anemones, tube-building worms and crustaceans, salps, tunicates, sea turtles, and even whales. So it's no surprise that several different groups of amphipods have become external parasites on fishes, which they cling to with specialized hook feet.

These parasitic forms have not been studied extensively. Most that are known to science are found on slow-moving, slow-growing bottom sharks and groundfish, many of them "ambush predators" of cold or deep waters, like the goosefish, sculpin, and flounder. These amphipods settle around their hosts' mouths, gills, pectoral fins, wounds, and anal vents and have specialized mouth parts, suggesting that they feed on uneaten food, mucous, skin tissue, and fish wastes.

Under the microscope the sea robin hitchhikers look a lot like other shrimplike members of the group, but with large, dark red, multifaceted eyes. They also have sizable hooked appendages that allow them to cling tenaciously to their hosts. They are members of Lafystiidae ("to swallow greedily"), an amphipod family that was first identified in 1888 off Nova Scotia as parasitic on fishes.

Determining the species of sea robin amphipods required expert opinion on a number of microscopic details of amphipod anatomy. They were eventually identified as male and female Lafystius frameae by Anne Frame, the Sandy Hook Marine Lab biologist who first recorded the species from samples taken from a New Jersey offshore sludge dumpsite in 1970. It was presumed at that time that they were parasitic, but the host fish was not known until now.

Sea robins are not noted in the scientific literature as being particularly bothered by diseases or parasites. References seem to indicate that only internal parasites like nematodes, cestodes and trematodes have been identified in them. This is likely related to the fact that since sea robins are not an important commercial species, no one has taken the time for a close look. We tend to forget that "every dog has a few fleas," especially in the sea, and often when examining the different possible lifestyles available to marine life - drifters, free swimmers, or bottom dwellers - the parasite is overlooked. In fact, simple arithmatic dictates that animals living a parasitic existence must be the most numerous creatures on earth. So life may not be as carefree for the sea robin as it seems. And it's no surprise to me that they are bothered by these "fleas" and probably other inconveniences. Some day a budding ichthyologist in search of a project will make a career out of studying sea robins or their parasites and discover that they are as exciting as many of our larger, more thoroughly studied species.

For now, those of us who are friends or foes of the "cock" robins will be satisfied (for different reasons) with the knowledge that as of September 1992, Lafystius framae, which greedily feeds, finally has a home, and that Prionotus, that greedy old bait-stealer, has a parasite.

Something to think about:

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