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Title: The impact of water exchange rate and treatment processes on water-borne hormones in recirculation aquaculture systems containing sexually maturing Atlantic salmon Salmo salar

Author
item GOOD, CHRISOTPHER - Freshwater Institute
item DAVIDSON, JOHN - Freshwater Institute
item EARLEY, RYAN - University Of Alabama
item LEE, ELIZABETH - University Of Alabama
item SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Journal of Aquaculture Research and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2014
Publication Date: 8/16/2014
Citation: Good, C., Davidson, J., Earley, R.L., Lee, E., Summerfelt, S. 2014. The impact of water exchange rate and treatment processes on water-borne hormones in recirculation aquaculture systems containing sexually maturing Atlantic salmon Salmo salar. Journal of Aquaculture Research and Development. 5(5):1-7. DOI: 10.4172/2155-9546.1000260.

Interpretive Summary: Precocious sexual maturation of male Atlantic salmon has been a repeatedly observed phenomenon at The Freshwater Institute as salmon are raised in freshwater recirculation systems up to market size (4-6kg). Due to numerous environmental and host factors that can influence the timing of salmon maturation, it is unclear at present what factor(s) are contributing to early maturation in our systems. We posited that the accumulation of steroid hormones in recirculated water may be influencing maturation, and we sought to examine this hypothesis during an ongoing high vs. low water exchange rate study in our six replicated water recirculation systems (WRAS). Using commercially available enzyme immunoassay kits to quantify hormone levels in water samples, we collected replicate (3) water samples from three locations within each WRAS: i) make-up water; ii) pre-unit processes (biofilter, degassing column, low-head oxygenator); and iii) post-unit processes. These water samples were tested for testosterone, 11-ketotestosterone, cortisol, estradiol, and progesterone, in order to determine: i) whether specific hormones were accumulating in WRAS relative to their exchange rate, i.e. high vs. low; and ii) whether the concentration of specific hormones was influenced by passage through the WRAS unit processes. We found that only testosterone accumulated in WRAS relative to water exchange rates, and 11-ketotestosterone was the only hormone reduced in concentration during passage through the WRAS unit processes. Because overall precocious maturation did not differ in populations raised at high vs. low exchange rates, it remains unclear as to how and why early male maturation remains an issue when raising Atlantic salmon to market size in freshwater recirculation systems.

Technical Abstract: 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.