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: In the present study, the accumulation and degradation of testosterone by Chlorella vulgaris were studied. The results showed that C. vulgaris has a significant ability to eliminate testosterone by bioaccumulation and biodegradation, and during the 96 h experimental period, the data demonstrated that the accumulation of testosterone followed a sigmoidal accumulation pattern. At the end of the experiment, the bioconcentration percentages of testosterone by C. vulgaris in the high-concentration group and the low-concentration group were 11.49 ± 2.78% and 40.10 ± 1.98%, respectively, and the biodegradation percentages of testosterone were 69.64 ± 4.33% and 42.48 ± 1.92%, respectively. The rate of biodegradation of testosterone by C. vulgaris mainly depended on the relative initial concentration of testosterone. When the relative initial concentration of testosterone increases, the degradation may gradually change from zero-order kinetics to second-order kinetics.

To improve release techniques of Japanese flounder, Paralichthys olivaceus, for the purpose of stock enhancement, the substrate preference and burial behaviour over a range of sand grain sizes were investigated under laboratory conditions. Ten 12‐hr trials (i.e. 10 experimental groups), which, respectively, contained two different levels of substrates, demonstrated that juvenile flounder (55–78 mm total length) selected substrate of grain size (GS) < 2.00 mm, and the degree (from high to low) of their preference could be listed as Level 3 (0.50–2.00 mm) > Level 4 (0.25–0.50 mm) > Level 5 (0.05–0.25 mm) > Level 2 (2.00–4.00 mm) > Level 1 (4.00–6.00 mm). The average burying of fish in substrates of GS < 2.00 mm was more than 93.1%. Additionally, along with food deprivation time increased from 12 to 24 hr, some flounder showed random off‐bottom swimming behaviour, and the appearance of off‐bottom swimming behaviour was <3.2%. These results suggest that releasing sites with appropriate substrate grain size (GS < 2.00 mm) are suitable for conducting mass releases of hatchery‐reared flounder juveniles, and starvation prior to release should be minimized. The results of the present study are essential to improve stocking strategies of Japanese flounder and reduce the juvenile mortality after release.

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