G. C. Kearn

Bio: G. C. Kearn is an academic researcher. The author has contributed to research in topics: Aquatic animal & Monogenea. The author has an hindex of 1, co-authored 1 publications receiving 36 citations.

Parasites as Indicators of Water Quality and the Potential Use of Helminth Transmission in Marine Pollution Studies

Abstract: Publisher Summary This chapter focuses on parasites as indicators of water quality and the potential use of helminth transmission in marine pollution studies. There are good reasons for focusing on parasitic organisms in general and helminth parasites in particular, in the search for highly sensitive indicators. First, there are more parasitic than free-living species. Second, helminth parasites have complex life cycles and the different developmental stages have widely differing requirements, therefore, each stage must be assessed separately for sensitivity to environmental change, thereby widening the choice of potential indicators. Many biotic and abiotic factors affect the numbers and distribution of marine. With regard to numbers, there is much information on prevalence, intensity, mean intensity, relative density or abundance, and diversity. In some instances, a parasite may be directly susceptible to the toxic effects of pollutants, in which case pollution may reduce infection prevalence and intensity. If the host is more susceptible than the parasite to the pollutant, its resistance to infection may be lowered, leading to higher prevalence and intensity.

The Eggs of Monogeneans

Abstract: Publisher Summary This chapter illustrates the role of the eggs in the biology of monogenean parasites. The life cycles of monogeneans are relatively simple compared with those of other parasitic platyhelminths (cestodes and digeneans). Most monogeneans inhabit the skin and gills of fishes, and these sites are accessible to free-swimming larvae (oncomiracidia) hatching from freely deposited aquatic eggs. This simple life cycle has sufficient evolutionary plasticity to enable monogeneans to adapt to fishes living in a range of marine and freshwater habitats and with strikingly different ways of life, such as bottom-living flat-fishes and fast-moving pelagic species. Greater evolutionary potential is revealed by the remarkable survival of monogeneans on those fish-like ancestors of the tetrapods that colonized the terrestrial environment, leading to monogenean life cycles of sometimes surprising complexity. The chapter focuses on hatching rhythms and hatching factors, which in many monogeneans are of fundamental importance in infection of new hosts, and the intriguing changes in reproductive biology that have accompanied the progressive attenuation of the ties between tetrapod hosts and the aquatic environment. Monogeneans deserve special attention, because they provide opportunities for direct observation of the egg assembly process and display a surprising variety of egg shapes and egg appendages, which have attracted little functional interpretation. Monogeneans show a remarkable diversity in the shape and size of their eggs and in their egg appendages. The possible significance of the shapes and sizes of monogenean eggs is discussed in the chapter.

Experiments on host-finding and host-specificity in the monogenean skin parasite Entobdella soleae.

Abstract: The oncomiracidium of the monogenean skin parasite Entobdella soleae finds its flatfish host, Solea solea, by chemoreception. The free-swimming larva responds to a specific substance secreted by the skin of the common sole, attaches itself to this skin and immediately sheds its ciliated epidermal cells. Larvae respond in the same way to agar jelly which has been in contact with the skin of S. solea.The oncomiracidia attach to S. solea skin in preference to that of other soleid fishes (Buglossidium luteum and Solea variegata), pleuronectid fishes (Limanda limanda, Pleuronectes platessa) and elasmobranch flatfishes (Raia spp.).Larvae respond strongly to isolated epidermis from Solea solea but show no response to the fish's cornea, indicating that the attractive substance is produced by the mucus cells in the fish's epidermis.The larvae attach with equal readiness to skin from the upper and lower surfaces of S. solea. Thus the preponderance of young parasites on the upper surfaces of soles is due not to a preference for the upper skin but to the fact that the lower skin is in contact with the substratum and cannot be reached by the larvae.These results led to speculations on the way in which host specificity evolved in the Monogenea.I am indebted to Mr J. E. Green of the Plymouth Laboratory for setting up a tank containing infected soles and for maintaining the tank and feeding the fishes for many months.I am also grateful to the Directors and Staff of the Plymouth Laboratory and the Fisheries Laboratory, Lowestoft, for hospitality and assistance. I am particularly grateful to Mr J. Riley of the Lowestoft Laboratory for providing various flatfishes.