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.

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During the Bremerhaven Workshop, ichthyoplankton samples were collected with horizontal subsurface hauls at 28 stations from the inner German Bight to the Dogger Bank. Directly after being caught fish embryos were examined a l~v e for morphological developmental defects under a dissecting microscope. Investigations on chromosomal aberrations were confined to preserved blastula stages of dab and were carried out later in the laboratory. Main species sampled were dab Limanda limanda, plaice Pleuronectes platessa, sprat Sprattus sprattus and whiting Merlangius merlangus. Because of their widespread distribution and high numerical occurrence, dab embryos were best suited for the detection of regional differences in malformation frequencies. The proportion of malformations in the most sensitive early developmental stage of dab reached 32 % in the inner part of the German Bight and fell to 9 % further offshore, increasing again at the Dogger Bank to values up to 31 %. Data collection was acconlplished with a computerized data sampling/evaluation/presentation system, and results concerning the morphological differences of malformation frequencies were available directly after observation. Thus, the method as described below proved to be a suitable approach for b~ological effects mon~toring. Anaphase aberration frequencies in dab en~bryos reached a peak of 63 % in the inner part of the German Bight, whereas the lowest value (51 %) was detected far offshore at a less polluted station; aberrations on the Dogger Bank were found to be 57 %. Investigations on the chromosomal aberrations in the same material used for the determination of morphological aberrations provided an opportunity to evaluate the potential effects of contaminants at the chromosome level.

Artificially inseminated eggs of feral North Sea whiting (Merlangius merlangus) were incubated in the laboratory in order to determine reproductive success. After incubation, two measures for reproductive success, total hatch and viable hatch, were determined and correlated with chlorinated hydrocarbon residues in the respective ovaries. From their specific toxicities and the sum of all determined chlorinated hydrocarbon contaminants, a contamination factor (CF) was calculated. Significant negative correlations were found between total hatch and DDT, including its metabolites (ZDDT), dieldrin and the CF. ZDDT and the CF were also negatively correlated with viable hatch. A threshold value of ovary contamination above which impairment of reproductive success was likely to occur was set at > 200 ~tg kg -~ wet wt. for ZPCB, > 20 ~tg kg -1 wet wt. for ZDDT and > 10 ~g kg -1 wet wt. for dieldrin.

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