Levels of 1 I -0xotestosterone (1 7 P-hydroxyandrost-4-ene-3, I 1 -dione) and testosterone in the blood serum of individually marked adult male Atlantic salmon held in captivity, were measured by radioimmunoassay at approximately monthly intervals for periods of up to 18 months. In addition to peak concentrations of both hormones shown by all the maturing fish at the time to full sexual maturation during October and November, a majority of maturing fish also showed a significant elevation of 1 1 -o,xotestosterone during the early months of the year. The possible involvement of this early elevation of 1 1-oxotestosterone in controlling the mitotic multiplication of spermatogonia is discussed. Weight and length increases expressed as specific values G w and GL and weight to length relationships for the maturing males for each sampling period are presented and compared with those of nonmaturing fish.

The illegal practice of using cyanide (CN) as a stunning agent to collect fish for both the marine aquarium and live fish food trades has been used throughout the Indo-Pacific for over 50 years. CN fishing is destructive to all life forms within the coral reef ecosystems where it is used and is certainly one of many anthropogenic activities that have led to 95% of the reefs in the Indo-Pacific being labeled at risk for degradation and loss. A field-deployable test for detecting fish caught using CN would assist in combating the use of this destructive practice, however, no reliable and robust test exists. Further, there is little toxicokinetic data available on marine fish to support the development of such a test, yet such data is critical to establishing the concentration range and time scale over which such a test would be viable. This study presents the first direct measurement of the half-life of the metabolite thiocyanate (SCN) after pulsed exposure to CN in a marine fish. SCN was measured in the plasma of Amphiprion ocellaris after exposure to 50 ppm CN for three exposure times (20, 45, and 60 s) using HPLC-UV and a C30 column pre-treated with polyethylene glycol. Plasma SCN levels observed are dose-dependent, reflecting a longer time for conversion of CN to SCN as the dose of CN increases. SCN plasma levels reached a maximum concentration (1.2–2.3 ppm) 12–20 h after exposure to CN. The half-life for the elimination of SCN was 1.01 ± 0.26 days for 45 s exposure and 0.44 ± 0.15 days for 20 s exposure. Fish were also directly exposed to SCN (100 ppm for 11 days) and the observed half-life for SCN elimination was 0.35 ± 0.07 days. Plasma SCN levels did not return to control levels, even after 41 days when exposed to CN but did return to control levels after 48 days when exposed to SCN. The similar half-lives observed for CN and SCN exposure suggests that SCN exposure can be used as a proxy for measuring the rate of SCN elimination following CN exposure. In order for plasma SCN to be used as a marker for CN exposure, these results must be extended to other species and endogenous levels of SCN in wild caught fish must be established.

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