The OECD validation study of the zebrafish embryo acute toxicity test (ZFET) for acute aquatic toxicity testing evaluated the ZFET reproducibility by testing 20 chemicals at 5 different concentrations in 3 independent runs in at least 3 laboratories. Stock solutions and test concentrations were analytically confirmed for 11 chemicals. Newly fertilised zebrafish eggs (20/concentration and control) were exposed for 96h to chemicals. Four apical endpoints were recorded daily as indicators of acute lethality: coagulation of the embryo, lack of somite formation, non-detachment of the tail bud from the yolk sac and lack of heartbeat. Results (LC50 values for 48/96h exposure) show that the ZFET is a robust method with a good intra- and inter-laboratory reproducibility (CV<30%) for most chemicals and laboratories. The reproducibility was lower (CV>30%) for some very toxic or volatile chemicals, and chemicals tested close to their limit of solubility. The ZFET is now available as OECD Test Guideline 236. Considering the high predictive capacity of the ZFET demonstrated by Belanger et al. (2013) in their retrospective analysis of acute fish toxicity and fish embryo acute toxicity data, the ZFET is ready to be considered for acute fish toxicity for regulatory purposes.
DNA barcoding, based on sequence diversity in the mitochondrial COI gene, has proven an excellent tool for identifying species in many animal groups. Here, we report the first barcode studies for freshwater zooplankton from Mexico and Guatemala and discuss the taxonomic and biological implications of this work. Our studies examined 61 species of Cladocera and 21 of Copepoda, about 40% of the known fauna in this region. Sequence divergences among conspecific individuals of cladocerans and copepods averaged 0.82% and 0.79%, respectively, while sequence divergences among congeneric taxa were on average 15-20 times as high. Barcodes were successful in discriminating all species in our study, but sequences for Mexican Daphnia exilis overlapped with those of D. spinulata from Argentina. Our barcode data revealed evidence of many species overlooked by current classification systems —for example, based on COI genotypes the Diapahanosoma birgei group appears to include 5 species, while Ceriodaphnia cf. rigaudi, Moina cf. micrura, Mastigodiaptomus albuquerquensis and Mastigodiaptomus reidae all include 2–3 taxa. The barcode results support recent taxonomic revisions, such as recognition of the genus Leberis, and the presence of several species in the D. birgei and Chydorus sphaericus complexes. The present results indicate that DNA barcoding will provide powerful new insights into both the incidence of cryptic species and a better understanding of zooplankton distributions, aiding evaluation of the factors influencing competitive outcomes, and the colonization of aquatic environments.
This paper reports on the assessment of the effect of Cd+2 and Cr+6 to the rotifers Brachionus calyciflorus and B. patulus using life table demography and population growth. Based on acute toxicity tests, cadmium was nearly 100 times more toxic than chromium for both the rotifer species. Age-specific fecundity curves of both the brachionids showed increased offspring beyond the age of 4 days and after that the production nearly stabilized for about 10 days and later declined. At any given treatment, B. calyciflorus had the higher rate of offspring production than B. patulus. For any given rotifer, increased metal concentration (Cd or Cr) resulted in decreased offspring production. While chromium at a concentration of 8.0 mg L(-1), permitted reproduction in B. calyciflorus, the egg production of B. patulus was inhibited at half that level (4.0 mg L(-1)). Cd at concentrations as low as 0.056 mg L(-1) caused 10-30% reduction in survivorship and reproductive parameters of B. calyciflorus. The lowest chromium concentration chosen for B. calyciflorus (0.5 mg L(-1)) had, however, a lower impact (2-22%) on the life history variables. Corresponding values of life history variables for B. patulus at the lowest Cd (0.0028 mg L(-1)) and Cr (0.25 mg L(-1)) concentrations varied greatly (2-40% and < 1-24%, respectively). Compared to controls, both the rotifer species in Cd or Cr treatments had lower densities. In controls, B. calyciflorus reached a peak abundance of about 100 ind. mL(-1), while the corresponding value for B. patulus was slightly higher (120 ind. mL(-1)). The rate of population increase (r) derived from the population growth data varied from +0.42 to -0.40 depending on the concentration of the heavy metal in the medium.
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