The effects of copper on the morphological and functional development of zebrafish embryos.

Waterborne copper exposure can exert a variety of physiological effects in fish, including the disruption of sensory system function, which has wide-reaching implications for fish behaviour. In developing fish larvae, copper is known to affect key parameters, such as survival and growth and more recently has been shown to interfere with the octavolateral system. The present study aimed to take a combined view of morphological (e.g. length, yolk sac area) and functional (e.g. heart beat, behaviour) processes to understand the complex effect of copper on fish development. In the first of two experiments, zebrafish embryos were exposed to a range of copper concentrations (11-1000 microg l(-1)) from fertilisation for a 72 h period. The greatest mortality was seen between 5 and 24h post-fertilisation (hpf) and was more pronounced at the higher copper concentrations. Copper also had an inhibitory effect on hatching. Length and yolk sac area of individuals were recorded across treatments at 72 hpf and elevated copper was found to slow development. Individuals from the higher copper treatments had the fastest heart rates at 28 hpf suggesting that stress responses were induced in the embryos during copper exposure. In the second experiment, embryos were exposed in a similar manner to two copper concentrations, based on those from Experiment 1 that resulted in <50% mortality. At 120 hpf, embryos exposed to both copper concentrations possessed significantly fewer functional neuromasts, an effect which was associated with a reduced ability to orientate in a current. Therefore, although mortality at these copper concentrations was low initially, and then almost non-existent after 24 hpf, the inability of copper-exposed larvae to orientate in a water current as a result of lateral line dysfunction is likely to seriously compromise survival.