A better understanding and utilization of the life history pattern Atlantic salmon can serve both to improve control of maturation and gamete use as well as serve determining the highest meat quality for human consumption. Earlier studies demonstrated that 82% of Atlantic salmon (AS) males matured under a 24-hour (hr) light (L) regime in comparison to 8% in 12:12 light:dark (LD) simulating natural conditions. Further, higher temperatures (16oC) and 24 hr L resulted in 47% maturation in comparison to no maturation at 5-10oC. Most recent observations have shown maturation taking place at 18oC (Martinez et al. 2024. JWAS). Our study explores the response of pre-smolt AS of mean initial weight 63 + 21 and 67.5 + 16.3 g (initial hot and cold water, respectively) kept in a small set up of flow-through or recirculated, side-by-side systems, allowing the predictable maturation of fish throughout the year. The recirculated system allowed adjustable temperature changes between 12 and 23oC within hours (Fig.1). Body weight reached up to 10- fold increase, however mean body weight has not differed between “Hot” and “Cold” regimes
after 2 cycles 407 +117 and 421 + 58 g, respectively. We present growth rate, maturation process, and fragmentary biochemical characteristics of fish muscle neutral (NL) and phospholipids (PL), fatty acids, blood osmolality, hematocrit) over a period of “shortened” light and temperature annual cycle. The first maturation of male AS releasing sperm was induced after 168 days of rotation of light and temperature cycles (Fig.2). Fish was 258g and gonadosomatic index (GSI) 5.2%. The first phase difference in experimental conditions between fish reared on commercial diet at temperatures 13.6 + 1.5 and 21.7 + 2.8oC under 12:12 LD and 24:L regimes, respectively, resulted in significant difference in muscle NL gamma-linolenic fatty acid, 34.1 + 10.6 and 16.9 + 1.8%, EPA 1.8 + 0.24 and 2.33 + 0.04, and PL DHA 17.6 + 1.4 and 15.7 +0.9%. We will present results of fatty acid profiles in the following 160 days of growth and maturation. These studies were supported by North Central Regional Aquaculture Center, USDA, and Ohio Agriculture Research and Development Center, O.S.U.