Tissue Damage Inflicted by Lernaea cyprinacea Linnaeus, a Copepod Parasitic on Tadpoles

Abstract

The site and extent of injury in 14 Rana pipiens experimentally infested with Lernaea cyprinacea were determined by the use of serial sections. Muscles and kidneys were the most frequent site of development of the anchor process, but lungs, liver, and spinal cord were also affected. The degree of injury was in part dependent upon the nature of the tissue invaded and in part upon the degree of development of the parasite. Injury to the host could be attributed to compression and destruction of tissues in contact with the expanding anchor process or to subsequent formation of connective tissue layers around the parasite. Although connective tissue was always found surrounding the portion of the copepod free in the coelom of the host, the tissues of the body wall failed to contribute to its formation. Thus, lesions on the integument of the host, common in fish infested with Lernaea cyprinacea, do not occur on infested Rana pipiens. Lernaea cyprinacea Linnaeus has been reported as parasitizing many different species of fishes throughout the world (Nakai, 1927; Tidd, 1934; Haderlie, 1953; Uzmann and Rayner, 1958; Haley and Winn, 1959; Huggins, 1959; Dogiel, Petrushevski, and Polyanski, 1961). Recently we have been finding specimens of Lernaea on tadpoles as well as fishes from central Ohio streams. This aroused our curiosity as to the part tadpoles might play as hosts to L. cyprinacea. We successfully infested laboratory-reared tadpoles of Rana pipiens with first copepodid larvae of L. cyprinacea (Tidd, 1962). Our observations of the deep penetration and development by the adult females in these hosts led us to make a study of the tissue sites and tissue damage resulting from these experimental infestations. MATERIALS AND METHODS Tadpoles of R. pipiens were laboratory raised from eggs obtained by induced ovulation. At the time of infestation these tadpoles were 25 mm long. They were divided into an experimental and a control group. Each tadpole in the experimental group was infested by the method outlined by Tidd (1962). The control tadpoles were treated the same in every respect except that they were not exposed to the larvae. The temperature of our laboratory during this experiment varied between Received for publication 2 October 1962. 22 and 28 C. We knew from past experience that 10 days after infestation the copepodid larvae mature to the point where some start a penetration of the host's integument and enter upon a period of metamorphosis. The body segments lengthen and the arms of the anchor process form as outgrowths of the cephalothorax. Ten days after penetration the metamorphosis of these parasites is complete or nearly so. Although all tadpoles were exposed to copepodid larvae of the same age, differences of 2 to 3 days in the time of penetration were common. Thus the copepods on any one tadpole may exhibit considerable differences in their degree of development depending upon the actual time of penetration. We divided our experimental and control tadpoles into three groups each. The first were killed 10 days after infestation, the second 15 days, and the third 20 days. Bouin's alcoholic reagent was used to kill and fix all specimens. The standard paraffin embedding method was used. Serial frontal and serial cross sections, 10 / thick, were cut from 14 of these infested tadpoles and their controls. The sections were stained with either Mallory's triple strain or a modification of Azocarmine-G (Hubschman, 1962). Effects of the development of the anchor process were determined by comparison with control tadpoles of approximately the same age.