MP13 Aquatic Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(FAR-1117-816253) Modified Japanese medaka embryo larval bioassay for rapid determination of developmental abnormalities.

Farwell, AJ¹, Nero, V¹, Croft, M¹, Bal, P¹, Dixon, DG¹, ¹ University of Waterloo, Waterloo, Ontario, Canada

ABSTRACT- The Japanese medaka (Oryzias latipes) embryo larval assay has been used extensively as a laboratory model for the evaluation of toxicant impacts. However, the naturally high variability in the time of hatch is a limitation in terms of the duration of the test. To improve the economic feasibility of this bioassay, we modified an 18 day test protocol by gently agitating the test containers to synchronize hatching and induce early hatching. For non-exposed embryos, the modified protocol with agitation resulted in median hatch times of 7 - 8 days compared to 9 - 14 days for the 18 day protocol without agitation. To determine whether agitation had any effect on the sensitivity of sublethal endpoints, the 18 day and modified protocols were compared using 2 different complex mixtures containing either polycyclic aromatic hydrocarbons (PAH EXT) or naphthenic acids (NA EXT). Agitation reduced time to hatch by ≥1/3 and improved hatch success (100%). The modified protocol was generally more sensitive for a stressor (ie. PAH EXT) which caused reduced hatch length and induced symptoms of blue sac disease (BSD) including heart, yolk sac-pericardial, and cranial-skeletal deformities but had no effect on time to hatch. In contrast, the 18 day test was more sensitive for a stressor (ie. NA EXT) that had no effect on hatch length, was a weak inducer of BSD symptoms but increased time to hatch. The data suggests that differences between the protocols may be a function of the chemical properties of the test compound(s) and their ability to induce BSD symptoms. Although there was variation in the sensitivity of the measurement endpoints for the modified protocol, this protocol is recommended as a cost effective and rapid method to screen the sub-lethal impact of toxicants on the early-life stages of fish.

Key words: embryo larval development, Japanese medaka, protocol, time to hatch