Fine-scale observations of the predatory behaviour of the carnivorous copepod <Emphasis Type="Italic">Paraeuchaeta norvegica</Emphasis> and the escape responses of their ichthyoplankton prey,Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>)

Paraeuchaeta norvegica (8.5 mm total length) and yolk-sac stage Atlantic cod larvae (4 mm total length) (Gadus morhua) larvae were observed in aquaria (3 l of water) using silhouette video photography. This allowed direct observations (and quantitative measurement) of predator–prey interactions between these two species in 3-dimensions. Tail beats, used by cod larvae to propel themselves through the viscous fluid environment, also generate signals detectable by mechanoreceptive copepod predators. When the prey is close enough for detection and successful capture (approximately half a body-length), the copepod launches an extremely rapid high Reynolds number attack, grabbing the larva around its midsection. While capture itself takes place in milliseconds, minutes are required to subdue and completely ingest a cod larva. The behavioural observations are used to estimate the hydrodynamic signal strength of the cod larva’s tail beats and the copepod’s perceptive field for larval fish prey. Cod larvae are more sensitive to fluid velocity than P. norvegica and also appear capable of distinguishing between the signal generated by a swimming and an attacking copepod. However, the copepod can lunge at much faster velocities than a yolk-sac cod larva can escape, leading to the larva’s capture. These observations can serve as input to the predator–prey component of ecosystem models intended to assess the impact of P. norvegica on cod larvae.     

Future use and development of prenatal diagnosis. Consumers' attitudes

The rapid progress of prenatal diagnosis and genetic tests makes it important to investigate attitudes towards this development. A total of 40 women and 20 men with personal experience of prenatal diagnosis for chromosome aberrations were interviewed about their moral opinion of the development. The majority (88 per cent) considered it certain or probable that all new methods developed will also be used in the future. The majority (62 per cent) were hesitant about testing for common disorders, e.g., diabetes mellitus and rheumatoid arthritis, but regarded it justified in some situations. One-third of the individuals (31 per cent) wanted some kind of restrictions for the use of the tests, but only 13 per cent recommended legislation for this purpose. The majority (84 per cent) believed that ethical principles are influenced by scientific progress. In most aspects, the women and their partners had similar attitudes. However, 82 per cent of the women but only 20 per cent of the men considered that the couple itself should decide about prenatal diagnosis. The results demonstrated a considerable respect regarding the difficult choices associated with the development of prenatal diagnosis, also among those who have decided in favour of the test. The study indicated a greater need for autonomy among women than among men.