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Title: Changes in sex steroids, growth hormone, and insulin-like growth factor-I during ovarian development in Rainbow Trout cultured within a recirculating system with 24-hour Light

Author
item Weber, Gregory - Greg
item DAVIDSON, JOHN - Freshwater Institute
item KENNEY, P. - West Virginia University
item GOOD, CHRIS - Freshwater Institute
item MANOR, MEGHAN - West Virginia University
item WELSH, C. - West Virginia University
item AUSSANASUWANNAKUL, AUNCHALEE - Kasetsart University
item SUMMERFELT, STEVE - Freshwater Institute

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2014
Publication Date: 3/20/2015
Citation: Weber, G.M., Davidson, J.W., Kenney, P.B., Good, C.M., Manor, M.L., Welsh, C., Aussanasuwannakul, A., Summerfelt, S.T. 2015. Changes in sex steroids, growth hormone, and insulin-like growth factor-I during ovarian development in Rainbow Trout cultured within a recirculating system with 24-hour Light. North American Journal of Aquaculture. 77:186-194. DOI: 10.1080/15222055.2014.987933.

Interpretive Summary: Rainbow trout are commonly cultured within aquaculture systems to one pound or less and marketed as pan-sized fillets. Production of larger rainbow trout provides a distinguishable product. Research that describes the growth performance and fillet quality of large rainbow trout is limited, particularly for trout cultured in environmentally friendly recirculating aquaculture systems. Even less is known of the physiological responses to such culture conditions and how this affects growth and fillet quality traits. We evaluated the growth performance and fillet quality attributes of all-female rainbow trout reared using freshwater recirculating systems under constant lighting and with around-the-clock feeding, and concomitant changes in reproductive and growth axis hormone concentrations. We previously reported that fish reached ~5 kg in 24 months and that growth and product yield declined beginning at approximately 22 months post-hatch, as fish reached later stages of ovarian growth. Here we report some ovaries exhibited atresia and no fish ovulated suggesting reproductive dysfunction is caused by the environmental conditions. Gradual changes in growth and fillet quality attributes during gonadal development were accompanied by gradual changes in hormone levels but no clear changes in hormones were associated with rapid changes in product quality traits observed around months 24-26. This research provides rainbow trout growth performance and fillet quality results, and physiological impacts that can be referenced for the development of recirculating system production plans.

Technical Abstract: Female rainbow trout (Onchorynchus mykiss) were cultured within a freshwater recirculating aquaculture system under 24-h constant lighting in 13oC water, and they were fed every six hours to near satiation. An opaque roof allowed surface light intensity to vary between <200 to ~1500 lx. Growth performance and fillet quality data as previously reported showed that fish reached ~5 kg in 24 months and that growth and product yield declined beginning at approximately 22 months post-hatch. Here we report changes in plasma concentrations of testosterone (T), estradiol-17b (E2), the maturation inducing steroid (MIS) 17a,20b-dihydroxy-4-pregnen-3-one (17,20bP), growth hormone (GH), and insulin-like growth factor-I (IGF-I), during months 14-26 post-hatch. Oocyte diameter was variable at the start of the study with most fish averaging <1 mm, and diameter increased to above 3.2 mm in the final two months, with migrating germinal vesicles indicating they were post-vitellogenic. Some ovaries exhibited atresia and no fish ovulated suggesting some reproductive dysfunctions. Testosterone and E2 began increasing between months 16 and 18, and while T continued to increase throughout the study, E2 changed little after month 20. The MIS, 17,20bP, remained near or below detection. Plasma GH remained relatively unchanged although values trended slightly higher during the final four months with GH being significantly greater at months 22, 24 and 26 compared with month 16 post-hatch. Plasma IGF-I was higher at the first time point, month 14 post-hatch, compared to months 20, 24, 25, and 26. In summary, gradual changes in growth and fillet quality attributes during gonadal development were accompanied by gradual changes in hormone levels but no clear changes in hormones were associated with rapid changes in product quality traits observed around months 24-26.