TOXICITY OF 4-CHLOROANILINE IN EARLY LIFE-STAGES OF ZEBRAFISH (BRACHYDANIO-RERIO) .1. CYTOPATHOLOGY OF LIVER AND KIDNEY AFTER MICROINJECTION

In addition to survival and hatching parameters, cytological alteratio ns in liver and kidney of 4- and 6-d old zebrafish larvae (Brachydanio rerio) following single microinjection of fertilized eggs at the germ -ring stage with 5, 12.5, and 25 ng 4-chloroaniline/egg were investiga ted by means of electron microscopy. Whereas survival remained unaffec ted, microinjection with 4-chloroaniline disturbed hatching of larvae. Hatching was delayed by microinjection of 12.5 ng 4-chloroaniline/egg and above when compared to controls. Cytological investigations revea led ultrastructural changes in both liver and kidney in a dose- and ti me-dependent fashion. In the liver, major cytopathological changes inc luded fenestration, fragmentation, and vesiculation of the rough endop lasmic reticulum, proliferation of atypical mitochondria, and atypical lysosomes. Furthermore, myelin whorls, lipid inclusions, and choleste rol crystals were increased, whereas glycogen stores were reduced. Ren al tubular cells displayed altered brush borders, proliferation of nuc leoli, atypical mitochondria, fenestrated, fragmented, and vesiculated RER cisternae, as web as giant lysosomes. Most of these effects indic ate cellular dysfunction (e.g., disturbance of lipid metabolism in the liver), whereas others illustrate general cellular stress-responses t o chemical aggression. Comparisons of results with those of previous s tudies based on conventional fish exposure prove the suitability and s ensitivity of microinjection bioassays with zebrafish eggs as an alter native to conventional early life-stage tests.