MORPHOLOGICAL AND CHROMOSOMAL-ABERRATIONS DURING EMBRYONIC-DEVELOPMENT IN DAB LIMANDA-LIMANDA

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 alive 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 accomplished 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 biological effects monitoring. Anaphase aberration frequencies in dab embryos 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.