In February/March 1983 and 1984 a survey of pelagic fish eggs was conducted in the western Baltic (Kiel Bight), employing a horizontally towed plankton net tl m ~ and 300 ~tm mesh). Maximum egg numbers in the upper meter of the S = 21 x 10 -3 salinity layer were 200-100 m -a. The most abundant eggs were cod (up to 142 eggs. 100 m-3), followed by plaice (up to 74 eggs. 100 m -3) and flounder (20 eggs. 100 m-3). A considerable percentage of embryos of all species displayed aberrant development..In 1983 18 % of cod, 22 % of flounder and 24 % of plaice eggs caught contained defective embryos; in 1984 this number was larger, ranging from 28 % in plaice over 32 % in cod to 44 % in flounder. Early developmental stages showed the highest malformation rates (up to 51% in the case of early flounder embryos). With progressive development, malformations decreased in numbers, being lowest prior to hatching. Highest rates of malformations were recorded in the Mecklenburg Bight in 1983. A second area with high incidence of malformation rates was located south and east of the island of Langeland. Several reasons, including environmental and anthropogenic factors, for the occurrence of malformed embryos in pelagic fish eggs are discussed. The potential of malformation rates in embryos of pelagic fish eggs as a tool for monitoring is considered.
Atlantic cod bearing pseudobranchial tumours were investigated from both North Sea and Baltic Sea areas. Light and electron microscopic studies revealed a tumorous structure previously described in cod from Atlantic and Pacific waters. Additionally, cysts, multinucleated cells and early stages of mitosis are described.These findings support the hypothesis that pseudobranchial tumours are instigated by a protozoan infection causing xenotumours associated with the pseudobranch organ. The cells contained in these lesions showed similarities to amoebae.
Malformation rates in embryos of dab, whiting, cod, flounder, and plaice in the southern North Sea have been monitored between 1984 and 1995 by quantitative investigations of developmental defects in eggs immediately after capture. Incidences were highest in near-coastal waters known to receive high pollution loads. For all species and all areas investigated, synchronous trends were found with intermediate incidences in 1984, maxima in 1987 and significant decreases thereafter. The variations are compared with trends in organochlorine residues in dab and plaice from the German Bight collected over the same period. Trends vary for different organochlorine substances, but the overall picture indicates elevated levels in the period 1984-1987 and decreasing concentrations thereafter. Although the general pattern is consistent with the trend in incidences, significant correlations were only found for malformations of dab and concentrations of p,p -DDE. Trends in concentrations of nutrients and hydrographic factors were also investigated, indicating a significant negative linear correlation between surface water temperature and incidence of malformed embryos of dab. The hypothesis is put forward that low temperature may predispose developing fish embryos to the impact of organochlorines.1996 International Council for the Exploration of the Sea
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