In most amoeboid cells, the main protein involved in motility is actin. Nematode sperm are an exception, and their amoeboid motility is based on major sperm protein (MSP). We have studied the localization of actin and MSP in spermatids and spermatozoa of Graphidium strigosum (Dujardin, 1845), a species which has elongate male germ cells in which organelles are easily identified. Electrophoreses of G. slrigosum sperm proteins indicate that the main protein band, about 15 kDa in molecular weight, is specifically recognized by an anti-MSP polyclonal antibody developed against MSP of Caenorhabditis elegans (Burke and Ward 1983). Actin is present in small quantities. Immunocytochemical observations reveal that actin and MSP have an identical localization in precise areas of the male germ cells. Spermatids are labelled as dots around a central unlabelled zone, and spermatozoa are labelled only at the level of the anterior cap. Observations in G. strigosum are similar to that previously obtained in Heligmosomoides polygyrus (Mansir and Justine 1996). Co-localization of actin and MSP in the anterior cap of the spermatozoon, the region associated with pseudopod production, does not demonstrate directly that actin is involved in amoeboid movements, but shows that the role of actin in the cytoskeleton of nematode sperm should be re-investigated.
The effect of host variables such as size and density, on the transmission of cercariae of Diplostomum spathaceum (Rudolphi, 1819) into a second intermediate fish host, rainbow trout, Oncorhynchus mykiss (Walbaum), was studied quantitatively in laboratory experiments under varying exposure conditions. Differences in the number of established metacercariae were noted in differently sized fish exposed singly to the same number of cercariae and in water volumes related to the body surface area of the host. When exposed (1) singly in an equal water volume or, (2) simultaneously in the same tank, no differences in recovery of metacercariae per fish were found between “small” and “large" hosts. The latter observation is valid for three water volumes tested using the same number of cercariae per host. No significant difference in metacercarial infection was revealed in similar sized fish exposed at different host densities. It appears that transmission is more influenced by cercarial density (number of cercariae per water volume) and fish size than by fish density. These experimental findings support the view that cercarial infection offish occurs by chance, presumably mainly in the gill region. Accordingly, in the field, individual fish size and cercarial density rather than fish population density, prevail in parasite transmission from snail to fish. This is of interest in coastal areas heated by cooling water, where fish growth and fish population density are enhanced.
Brachylecithum microtesticulatum Timon-David, 1955 (Digenea: Dicrocoeliidae) is recorded for the first time in the Black Sea region. The morphology and variability of the digeneans recovered from Larus argentatus in Bulgaria and the Ukraine are described and compared with the redescription of the species (Bartoli and Mas-Coma 1989). Lyperosomum lari Travassos, 1917 of Smogorzhevskaya (1976) is considered a synonym of B. microtesticulatum.
Proteocephalus macrophallus (Diesing, 1850), considered by several authors as species inquireruia, was recently found in Cichla ocellaris in Venezuela. This material is compared with voucher specimens from the same host (C. ocellaris) from Brazil, identified and redescribed as P. macrophallus by Woodland (1933). The specific status of P. macrophallus is confirmed. This species is characterized by: 1 ) the shape of the body, which is wide and short, 2) the absence of a neck, 3) the distribution of the vitelline follicles, which converge posteriorly to the ovarian lobes, and 4) the structure of the uterus, which is evacuated in the last proglottides and transformed to thick-walled diverticles apparently separated each from other. A neotype is designated.