Occurrence and Pathology of Ligula intestinalis Infections in British Fishes

Abstract

Infection of British freshwater fishes with the plerocercoid larva of Ligula intestinalis is most widespread and common in the roach. It is less common in gudgeon, rudd, bream, and minnow, and rare in dace. Roach fry may become infected within the first 3 months of life. Infections in roach exceeding 13 cm in length are infrequent. Data concerning the size distribution of plerocercoids in fish of different size are given. In infected roach, the liver weight, packed cell volume of erythrocytes and hemoglobin are reduced. Gonadal retardation is a universal consequence of infection. It is severe in roach, rudd, bream, dace, and minnow but is less marked in gudgeon. Plerocercoid larvae of pseudophyllidean cestodes of the family Ligulidae have been recorded from the body cavity of numerous species of freshwater fishes in many parts of the Northern Hemisphere. Early accounts concerning the genus Ligula were reviewed by Cooper (1918). He recognized only the single species L. intestinalis (L.) and listed 63 species of host fish from many different families. More recently, Russian workers have suggested that at least two genera and five species, including L. intestinalis, are involved and that the plerocercoid larva of each species is restricted to a relatively narrow range of host species (Bykhovskaya-Pavlovskaya et al. 1962). In Britain the plerocercoids of Ligula intestinalis (L.) have been previously recorded from the roach (Rutilus rttilus) (Baylis 1928, 1939; Smyth, 1947; Kerr, 1948), gudgeon (Gobio gobio) (Baylis, 1939), brown trout (Salmo trutta) (Baylis, 1939) and minnow (Phoxinus phoxinu s) (Archer, pers. comm.). The only other member of the family Ligulidae which has been found in British fish is Schistocephalus solidus (Muller), the plerocercoid larva of which is restricted to the stickleback (Gasterosteus aculeatus). Despite numerous records of plerocercoids of Ligula intestinalis parasitizing fish, there have been relatively few accounts of the incidence and intensity of the infections encountered. Kosheva (1956) and Zitnian (1964) have provided data concerning infections in bream (Abramis brama) and roach respecReceived for publication 20 November 1967. * Present address: Department of Biology, Rice University, Houston, Texas. tively in Eastern Europe; Pitt and Grundmann (1957) described infections of the yellow perch (Perca flavescens) in the USA, and Van Cleave and Mueller (1934) discussed its incidence in the fishes of Oneida Lake, New York. The presence of Ligula intestinalis pleroc rcoids has been shown by many workers to be associated with certain pathological effects in the fish host (see Dogiel et al., 1961). Most of these reports originate in the USSR where ligulosis presents a serious problem in p sciculture. Blood changes associated with L. intestinalis infection, in particular an increase in the monocyte and polymorphonuclear leukocyte counts, have been described in the gudgeon by Sadkovskaya (1953) and in the crucian carp (Carassius carassius) by Shpolyanskaya (1953). The latter author also noted a fall in blood hemoglobin; a similar decrease was observed by Kosheva (1956) in bream infected with Ligula intestinalis and with the related species Digramma interrupta. Kosareva (1961) found that in roach, bream, and white bream (Blicca bjoernka) infected with L. intestinalis and D. interrupta the liver glycogen levels tended to be lower than in noninfected fish. Kosheva (1956) stated that infections with either species of tapeworm tended to depress the fat content of bream, and Pitt and Grundmann (1957) found that the rate of growth of yellow perch infected with L. intestinalis was lower than that for noninfected individuals. A commonly noted feature of infection with L. intestinalis plerocercoids is the inhibition of host gonad development. The most specific references to this condition are those of Kerr (1948), Kirschenblat (1951), and