The Japanese medaka (Oryzias latipes) early-life-stage bioassay (18-day test) provides a suitable laboratory model for the evaluation of toxicant impact. The naturally high variability in the time to hatch for medaka embryos is, however, a major limitation in terms of the duration of the test. In this study, the 18-day test was modified to use agitation to synchronize hatch and reduce time to hatch for nonexposed embryos. Then, bioassays were conducted using two different complex mixtures (polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (NAs)) to compare the sensitivity of the measurement endpoints using the 18-day standard protocol (SP) and the modified protocol (MP). Agitation reduced time to hatch by one third or more and improved hatch success (100%). The MP proved to be a more sensitive test method for the sublethal evaluation of a stressor (PAH mixture) that caused reduced hatch length and induced signs of blue sac disease (BSD) including heart deformities, yolk sac-pericardial edema, and cranial-skeletal deformities. In contrast, there was some variability in the sensitivity of the test methods for developmental endpoints for the sublethal evaluation of a stressor (NA mixture) that had no effect on hatch length and was a weak inducer of signs of BSD. Even though the sensitivity of the measurement endpoints were slightly more or less sensitive for the MP vs. SP depending on the mixture tested, the MP using agitation is recommended as a cost-effective and rapid alternative for screening the sublethal impact of toxicants on the early-life stages of fish.
Croft, B.A., and Croft, M.B., 1993. Larval survival and feeding by immature Metaseiulus occidentalis, Neoseiulus fallacis, Amblyseius amtersoni and Typhtodromus pyri on life stage groups of Tetranychus urticae Koch and phytoseiid larvae. Exp. Appl. Acarol., 17: 685-693.When 20 newly hatched larvae either ofMetaseiuhts occidentalis (Ncsbitt), Neoseiulusfallacis (Garman), Amblyseius ande~woni Chant or T),phtodromus pyri Scheuten were held in arenas without food at 95% RH and 20cC, the percentages of mites surviving to protonymphs were 5.0, 81.3, 86.3, and 83.8%, respectively. Unfed M. occidentalis larvae starv'ed within 2-3 days, while immatures of the other three species lived up to 12-14 days, with some becoming adults by cannibalizing and/or scavenging. Phytoseiid larvae given eggs, larvae/protochrs, salis/protonymphs (L/P), deutochrysalis/deutonymphs (D) or teleiochrysalis/female adult (T/A) of Tetranychus urticae Koch, fed at different incidences during 6 h tests. Larvae of T. pyri never ted, but almost all larvae of M. occidentalis fed on eggs and L/Ps and 60-70% of M. occidentalis larvae fed on Ds and T/As. N. fallacis and A. andersoni larvae ted at incidences from 20-75% depending on the stage of spider mite given. Larvae fed more commonly on eggs and L/Ps than Ds and T/As for M. occidentalis and N. fallacis but not A. andersoni. Protonymphs and deutonymphs of all four species readily ted on T/As after 3 h of exposure, but incidences were higher for A. andersoni and 7". pyri. Feeding on phytoseiid larvae by protonymphs and deutonymphs also was more common forA. andersoni and T. py14. Except for M. occidentalis, deutonymphs fed more than pmtonymphs on phytoseiid larvae. Results are discussed in relation to individual species' life histories and the value of these traits in predicting a species" role in a biological control system.
Alkylated polycyclic aromatic compounds (PACs), which are rich in dibenzothiophenes, are present in natural and reclaimed aquatic environments in the oil sands region of northern Alberta (Canada). An oil sands-derived PAC extract has been shown to induce signs of blue sac disease in Japanese medaka (Oryzias latipes) embryos. Information regarding exposure to and effects of oil sands PACs is available, but little of this information concerns the impact of modifying factors. The present study focuses on the effect of simulated solar radiation on oil sands-derived PAC toxicity to Japanese medaka embryos. Photomodification of the oil sands PAC extract caused reduced toxicity with an increase in the duration of ultraviolet (UV) exposure. Generally, mortality and developmental endpoints and, to a lesser extent, growth were affected by photomodification. Coexposures of the PAC mixture and UV caused slight increases in toxicity for mortality and embryonic developmental endpoints at the longest duration of UV exposure tested (16 h). Based on the modest phototoxicity of the oil sands PAC extract to Japanese medaka embryos, enhanced toxicity associated with UV irradiation may not be a concern for embryos of fish species that are common to the oil sands region. However, testing the effects of differing levels of UV irradiation on larval fish and invertebrates that may differ in their PAC bioaccumulation would improve our understanding concerning the importance of UV irradiation as a modifying factor in oil sands environmental risk assessment.
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