Life History of Ascocotyle mcintoshi Price, 1936 (Trematoda: Heterophyidae)

Abstract

The trematode utilizes the prosobranch freshwater snail, Littoridinops monroensis, in which a simple redia produces an ophthalmogymnocephalous type of cercaria, notably different from the pleurolophocercous and parapleurolophocercous cercariae reported for other species in the Ascocotyle complex. The method of infecting the fish hosts, Poecilia latipinna and Gambusia affinis, is unique in that the cercaria is ingested and penetrates through the intestinal wall to the coelom. Metacercariae produce thickwalled cysts attached to the viscera. Adults were produced within a 48 to 60-hr period by feeding metacercariae to day-old chicks. Price (1936) described Ascocotyle mcintoshi from the small intestine of the white ibis, Guara alba, from Florida. This is a report on the life history of this trematode in which the prosobranch snail, Littoridinops monroensis (Frauenfeld) (identified by Dr. F. G. Thompson, Florida State Museum, Gainesville, Florida), was found to serve as the first intermediate host and small fishes, Poecilia latipinna and Gambusia affinis holbrookii, serve as second intermediate hosts. Day-old unfed chicks were used as experimental definitive hosts. Sogandares and Lumsden (1963) reviewed the status of the Ascocotyle complex and listed 25 species which they separated into three subgenera. They retained within the genus Ascocotyle Loos, 1899, the subgenus Ascocotyle Travassos, 1930, and the subgenus Phagicola Faust, 1920. They established a new subgenus Leighia and placed in it A. mcintoshi, as the type species, and A. megalocephala Price, 1932. Since the above revision appeared, additional species have been added to the Ascocotyle complex: A. (L.) chandleri Lumsden, 1963, which becomes the third species in the subgenus Leighia, A. (A.) pachycystis Schroeder and Leigh, 1965, and A. sexidigitata Martin and Steele, 1970. Stein (1968) referred to an undescribed species of the genus which he found as metacercariae in the viscera and musculature of the fish, Cyprinodon variegatus. He was unable to obtain the adults from experimental hosts, but found a resemblance of metacercariae with adults, taken from two American mergansers, representing an undescribed species related to A. pachycystis. Received for publication 3 August 1972. Few complete life histories of species in the genus Ascocotyle complex are known. Scott (1964) reported the life history of A. (P.) diminuta (Stunkard and Haviland, 1924) Stunkard and Uzmann, 1955. SogandaresBernal and Lumsden (1963) concluded that A. diminuta is a synonym of A. angrense Travassos, 1916. Schroeder and Leigh (1965) reported the life history of A. pachycystis and Stein (1968) made many observations on the rediae, cercariae, metacercariae, and adults of A. leighi Burton, 1965, A. pachycystis, A. angrense, and A. ampullacea Miller and Harkema, 1962. Observations on metacercariaadult transformations have been made by others on several additional species. MATERIAL AND METHODS The snail host, Littoridinops monroensis, was collected in the field and reared in the laboratory in aerated tap water containing about 10% seawater. While it seemed to do well on decayed lettuce, it was routinely fed on the periphyton grown on vertical glass plates placed in aquaria exposed to sunlight. Poecilia latipinna and Gambusia affinis holbrookii used for infection were reared in the laboratory and exposed to cercariae individually in small dishes. Morphology of the larval stages was studies with the aid of a phase microscope. Redial and cercarial measurements were made on specimens fixed in hot 10% formalin. Metacercariae and adults were fixed in hot AFA solution and stained in Semichon's carmine. Measurements of these latter stages were made on mounted material. All measurements cited are given in microns. Day-old unfed chicks were infected orally by pipette and fed on either Purina Startena or a crumbled dried fish diet. The chick appears to be a satisfactory laboratory host for bringing A. mcintoshi to sexual maturity.