Three hundred and sixty‐nine cod Gadus morhua were individually marked and caged for 19 months. During this period, each cod was inspected several times for Lernaeocera branchialis . Growth in four groups of cod, identified by their infection history, were compared. During the caging, 79% of the cod remained uninfected, 8·5% were infected, but lost the parasite, 8% were infected with one parasite and 4·5% were infected with more than one parasite. The infected fish either harboured the parasite at caging or were infected during the study period. The highest rate of increase, both in body mass and in standard length ( L S ), was recorded in the group of male fish infected with one parasite throughout the experimental period. Conversely, those males free from infection showed significantly lower growth. The observed differences in growth could not be explained by changes in variables related to reproductive strategies. The alternative explanation for these results is that resistance to L. branchialis was associated with costs in terms of reduced growth of body mass and L S .
Two new species of myxosporeans are described from the gall bladders of hoki, Macruronus magellanicus Lönnberg, 1907, caught in the Southeast Pacific off Chile and in the Southwest Atlantic off the Falkland Islands. Pseudalataspora kovalevae n. sp. is described morphologically and genetically. Of the 12 species of Pseudalataspora previously described from the gall bladders of marine fish, P. kovalevae is most similar in morphology to P. umbraculiformis Gaevskaya and Kovaleva, 1984. The 18S rRNA gene sequence from P. kovalevae is the first for a member of the genus Pseudalataspora. Based on currently available myxosporean 18S rRNA gene sequence data, P. kovalevae shares greatest sequence identity with species of the genus Ceratomyxa (C. anko and C. pantherini). Palliatus magellanicus n. sp. is described morphologically only; it differs considerably in morphology, host species and locality from the five other Palliatus species described from marine fishes. A third species from the gall bladder is also described morphologically and genetically. On the basis of its morphology it is tentatively identified as Myxidium baueri Kovaleva and Gaevskaya, 1982, for which M. magellanicus is a new host record. Molecular analysis indicates that, of those species for which data are available, M. baueri is most closely related to Myxidium coryphaenoideum Noble, 1966 based on 18S rRNA gene sequence data, though support for a phylogenetic grouping is low.
Abstract Visceral organ topography (VOT) in marine teleosts has been defined as the “spatial arrangement and contiguity of organs within the body cavity”, and it has been suggested that VOT may influence the habitat(s) occupied by the third-stage larvae (L3) of ascaridoid nematodes. Reports of an asymmetrical distribution of Anisakis (“whaleworm”) L3 and Pseudoterranova (“sealworm”) L3 in Atlantic cod Gadus morhuaL. prompted studies of VOT in this host. The left liver lobe dominates the left sagittal half of the body cavity and is largely contiguous with the stomach wall. Examination of ã 630 cod confirmed that more L3 occur in the left than in the right body musculature. Two hypotheses discussed in relation to the asymmetry both pertain to the liver. Feeding and growth of larval ascaridoids in fish are discussed briefly.
To study the infection dynamics of metacercariae of the digenean Cryptocotyle lingua , wild living Atlantic cod, Gadus morhua , were caged for 18 months close to the shore. Here they were exposed to naturally occurring transmission stages of the parasite. First, both the abundance and the variance to mean ratio of metacercariae increased, but during the second half of the study the abundance levelled out, and the variance to mean ratio showed a significant decrease. Host mortality was negligible throughout the study. Based on the relationship between pigment spots and metacercariae observed by skin digestion, there was no indication of density-dependent parasite mortality. We conclude that the infrapopulations of metacercariae on the caged cod probably were regulated by density-dependent host responses acting against the cercariae.
A new species of myxosporean parasite is described from the gall bladders of the hakes Merluccius capensis Castelnau and M. paradoxus Franca (Pisces: Teleostei) caught off the west and south coasts of South Africa. The new species, Pseudalataspora vanderlingeni, is described morphologically and molecularly and compared with the 15 other species of Pseudalataspora previously described from marine fish. Although a molecular description is available on GenBank for only one of these 15 species, the morphological description supports the status of P. vanderlingeni as a new species. Earlier reports, without detailed descriptions, of Leptotheca sp. and Ceratomyxa sp. from the same hosts caught off Namibia were very likely to have been of P. vanderlingeni. These earlier studies reported high prevalences of infection, similar to those of >60% described in the present study. The effects of fixation and freezing on the dimensions of spores of Pseudalataspora spp. are described, and the status of the genus Pseudalataspora within the family Ceratomyxidae is discussed.
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