Chronic toxicity studies were conducted with an alga (Selenastrum capricornutum), a cladoceran (Daphnia magna) and the fathead minnow (Pimephales promelas) to determine their relative sensitivities to tebuthiuron, a soil‐applied herbicide. The alga was the most sensitive of the three species. The no observed effect concentrations for the studies with the fathead minnow (9.3 mg/L) and the cladoceran (21.8 mg/L) were higher than the algistatic concentration (1.5 mg/L) for Selenastrum. These concentrations are 8 to 121 times higher than the highest transient concentration of tebuthiuron reported for a catchment pond.

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A modification of photographic techniques for measurement of fish lengths has been developed, which uses instant photography and a digitizing tablet with a minicomputer. Instant photography allows print inspection while live fish are retained and “retakes” of poor quality photographs can be made. A photographic record of test animals is obtained, and fish may then be measured from the photographs at any convenient time. The digitizing tablet decreases time for fish measurement from photographs and maintains or improves accuracy over manual techniques. Raw data are entered directly into the minicomputer, which is programmed to perform summary statistics after all groups are measured. Summary statistics and raw data are printed to a prescribed format by the computer. The elimination of manual data entry and subsequent data validation will result in a substantial savings in time.