Blackspot flatworm

Uvulifer ambloplitis

ORDER Strigeatida

FAMILY

Diplostomatidae TAXONOMY

Uvulifer ambloplitis (Hughes 1927) Ceryle alcyon, Helisoma trivo-lvis, H. campanulatum, Ambloplitis rupestris, Micropterus dolomieu, Aplites salmoides, Eupomotis gibbosus, Apomotis cyanellus, Enneacan-thus obesus.

OTHER COMMON NAMES English: Black grub.

PHYSICAL CHARACTERISTICS

Adults are spoon-shaped with a broad body, thinner "neck," and a slightly broader cocked "head." The oral sucker is small and foremost on the fluke, with a small ventral sucker about halfway back on the head, and a holdfast organ just behind the central sucker. Adults range from 0.08-0.09 in (1.8-2.3 mm) long. Two testes are present, one in front of the other in the posterior half of the animal. The comparatively small ovary is located in front of the anterior testis. A common genital pore opens at the posterior tip of the animal.

DISTRIBUTION

Northern tip of South America, Central America, and much of North America.

HABITAT

The first intermediate hosts are snails, including Helisoma trivo-lvis. Second intermediate hosts are commonly green sunfish

(Lepomis cyanellus) and bluegill (L. macrochirus). The most common definitive host is the bird known as the belted kingfisher (Megaceryle alcyon). Sporocysts migrate to the digestive gland and liver of snails. Cercarial bore through the skin of fish, and cysts appear.

BEHAVIOR

Eggs of this species hatch into miracidia within a month. The ciliated miricidia burrow into their snail intermediate hosts, and develop into first-generation sporocysts. Second-generation sporocysts spread to the snail's digestive gland and liver, where they produce cercariae about six weeks after the initial infection. The cercariae leave the first intermediate host, swim to, and penetrate the skin of sunfish, bass, perch, and other fishes. They drop their tails and develop into metacercariae that encyst and are surrounded by host melanocytes that appear as hard black spots in the fish's skin. (Other species of Diplostomatidae and Strigeidae also produce black spots in fishes.) When kingfishers eat the infected fish, the worms mature within the host's intestine in about a month. Eggs deposited are passed by the bird through its feces into the snail's environment.

FEEDING ECOLOGY AND DIET

The black-spot flatworm depends for its nutrition on host species, including the ram's horn snail (Helisoma species); per-cid fishes; and birds, especially belted kingfishers.

REPRODUCTIVE BIOLOGY

Eggs are about 0.00004 in (1 pm) long and 0.00002 in (0.5 pm) wide; the miracidia are ovate and broader at the anterior end. The life cycle of the black-spot flatworm follows the prevalence and activity of its two host species. Cercariae begin appearing in the fish hosts in late spring following a 21-day development period. The snails continue to shed cercariae throughout the summer. The cercariae resemble tadpoles with a forked tail.

CONSERVATION STATUS

Not listed by IUCN.

SIGNIFICANCE TO HUMANS

Infections with metacercariae appear as black spots in several species of game fish. Their appearance sometimes discourages humans from eating them, even though there is no danger, especially when cooked. "Blackspot disease" is sometimes fatal to fish fry. ♦

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