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Development of a Methodology for Successful Multigeneration Life-Cycle Testing of the Estuarine Sheepshead Minnow, Cyprinodon variegatus.
Citation:
CRIPE, G. M., R. L. HEMMER, L. R. GOODMAN, AND J. VENNARI. Development of a Methodology for Successful Multigeneration Life-Cycle Testing of the Estuarine Sheepshead Minnow, Cyprinodon variegatus. ARCHIVES OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY. Springer, New York, NY, 56(3):500-508, (2009).
Impact/Purpose:
Refinement of methodology developed to test Sheepshead Minnows exposure to endocrine disruptors.
Description:
Sustainability of wildlife populations exposed to endocrine disrupting chemicals in natural water bodies has sparked sufficient concern that the U.S.EPA is developing methods for multiple generation exposures of fishes. Established testing methods and the short life-cycle of the sheepshead minnow, Cyprinodon variegatus, make this species particularly suitable for use in identifying potential adverse impacts of contaminants in estuarine and marine environments. This study documents refinement of life-cycle exposure methods used to increase the reliability of the assessment of sheepshead minnow reproduction and reduce the time to maturation for larvae and juvenile fishes. A test of three spawning chamber designs, three sex ratios, and two photoperiods identified conditions that reduced the coefficient of variation in egg production from > 100 percent to as little as 32 percent. Reliable results were produced with groups of three female and two male fishes (all of similar size) when they were placed in a rectangular chamber and acclimated for 10 days. A test water temperature of 26.5 + 2°C and a 14L:10D photoperiod resulted in fish producing a mean of 74 embryos per female per day with a coefficient of variation of 31.8 percent. Fertility of eggs exceeded 90 percent; embryos containing < 77 percent yolk hatched at < 45 percent, and normal embryos (>80 percent yolk) hatched at 95 percent. The time to maturation from larvae to spawning adult fishes was reduced to approximately 60 days post-hatch by feeding them flake food twice daily to satiation for 15 minutes, and it was observed that size (> 2.7 cm SL) was critical for spawning readiness. Adult fish were prepared for the spawning assessment by adding frozen brine shrimp to their diet. Results of these experiments provide methods to increase the reliability of reproduction measures and reduced test duration for multiple generation assays with the model estuarine fish, sheepshead minnow.