Journal of Aquaculture Research & Development

Abstract

The Impact of Water Exchange Rate and Treatment Processes on Water-Borne Hormones in Recirculation Aquaculture Systems Containing Sexually Maturing Atlantic Salmon Salmo salar

Christopher Good, John Davidson, Ryan L Earley, Elizabeth Lee and Steven Summerfelt

A controlled seven-month study was conducted in six replicated water recirculation aquaculture systems
(WRAS) to assess post-smolt Atlantic salmon (Salmo salar) performance in relation to WRAS water exchange rate. Unexpectedly high numbers of precocious sexually mature fish were observed in all WRAS toward the end of the study period; therefore, a separate investigation was conducted to quantify the levels of water-borne hormones (cortisol (C), testosterone (T), 11-ketotestosterone (11-KT), progesterone (P), and estradiol (E2)) to determine the impact of WRAS exchange rate, as well as transit through the unit processes, on soluble hormone concentrations.Triplicate water samples were collected at three separate sites in each of the six WRAS: pre-unit processes, post-unit processes, and at the makeup water influent. Water samples were concentrated and separate quantifications were carried out for each target hormone using enzyme immunoassay kits. Results indicated that among the hormones examined, only T was associated with higher concentrations in low exchange WRAS compared to high exchange WRAS. Water passage through the unit processes was associated with a significant reduction in concentration of
11-KT, in both high and low exchange WRAS. Water-borne concentrations of T, 11-KT, and E2 were significantly higher than influent makeup water; the majority of C and P concentrations were not significantly different between WRAS and makeup water samples. No significant differences were noted in the prevalence of apparently sexually mature fish or gonadosomatic indices in either sex between treatments, except a significantly higher prevalence of apparently mature female fish in low exchange WRAS. Overall, these findings suggest that, under the conditions of this study, C, P, E2, and 11-KT do not accumulate in lower exchange WRAS, and that, aside from 11-KT, the WRAS unit processes do not impact hormone concentration. Furthermore, the observed precocious sexual maturation was mostly unrelated to WRAS exchange rate.