Salmo trutta L. and Cyprinus carpio L. were exposed to low levels of waterborne heavy metals, 0.75 mg Ni drn-,, 1.06 mg Zn dm-3, 0.29 mg Cu dm-3 and 1.01 mg Cr dm-3, at pH 7.83, water hardness 206.9 mg CaCO, dm-,, and water temperature 15.5" C. During a 38 week exposure period, the humoral antibody response to MS2 bacteriophage was followed using a 50% viral neutralization assay (SD,,) method. A suppression of the immune response was observed in fish exposed to the four heavy metals. Total suppression of the humoral antibody response was found only in C. carpio exposed to Cu or Cr, and these fish exhibited symptoms of acute toxicosis. The time for the primary blood clearance of live bacteriophage was increased in S. trutta exposed to the heavy metals, with the exception of Zn-exposed fish, and in C. carpio exposed to Cu. Following the suppressed primary responses, the Ni-exposed S. trutta and Zn-exposed C. carpio exhibited an adjuvant-like response to the second bacteriophage challenge.

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The humoral antibody response to single intraperitoneal inoculations of MS2 bacteriophage was followed in Salmo trutta using a 50 % bacteriophage neutralisation titre ( s D~~) method.Immune memory was observed with enhancement of both the time and level of antibody production, though an initial suppression was observed 7 days after secondary inoculation. Antibody titres were related to MS2 concentration, and adjuvants were found to enhance the response. An increased enhancement of antibody production by Freund's complete adjuvant over that of incomplete adjuvant was observed.

Six juvenile specimens of Pleuragruntma antarcticum, caught near King George Island, Antarctica, were found to be parasitized by the plerocercoid stage of a pseudophyllidean cestode. A similar 100% incidence of infection was noted by Bartsch (1985) in her study of P. antarcticum. The infestation ranged from 4 to 17 plerocercoids per fish, with each of the 1-2.5 mm long parasites associated loosely with the stomach or intestinal mesentery of the host. The host response to the parasite, a discrete inflammatory sheath that was not visible to the naked eye, was observed by light and scanning electron microscopy.The specimens were fixed in 0.1 M phosphate buffer, pH 7.4containing4Y0 paraformaldehyde-0.2% picric acid, for 24 h at 4" C . Dehydration was achieved with a graded series of glycol-methacrylate monomer (BDH). For light microscopy the specimens were embedded in glycol-methacrylate (JB4; Polysciences) and 2-pm sections taken. An aqueous 1 % (w/v) methylene blue, 1 YO (w/v) basic fuchsin solution. added 1 : 1 to 0.2 M phosphate buffer, pH FIG. I. Plerocercoid tegument and host inflammatory tissues. (a) TS x 375, methylene blue-basic fuchsin stained, (b) SEM x 390. c, inflammatory capsule of host; I, leucocytes and debris on the tegument: m, plerocercoid mesenchyme; 1, plerocercoid tegument with microtriches visible on the outer surface. Arrows indicate host macrophages. 23 1 0022-1 I12/87/31A231+02$03.00/0 0 1987 The Fisheries Society of the British Isles

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A primary challenge of MS2 bacteriophage was cleared from the blood of the teleost Salmo trutta within 2.5 days. In contrast the clearance of a 2nd challenge required an extra 3.5 days and the induction of the secondary antibody response was delayed, though immune memory was observed later.