World Aquacluture Magazine - September 2020

54 SEP TEMBER 2020 • WORLD AQUACULTURE • WWW.WA S.ORG Photoperiod and Temperature Manipulation Starting in the early 1990s, the aquaculture program at the State University of NewYork (SUNY) at Cobleskill examined daylength and temperature manipulation as a strategy for improving gamete viability. The strategy was to provide Arctic char with light and temperature regimes similar to Labrador, the source of the Fraser River Arctic char grown at SUNY. Daylength was controlled and chillers were placed on tanks to cool the water throughout the summer and early fall. In November, when ambient surface water temperatures reached 10C, broodstock were moved to outdoor tanks to experience falling colder temperatures to induce spawning. Under these conditions, Arctic char ovaries matured from December to February. Arctic char were artificially spawned using dry (2 min) and then wet (2 min) spawning techniques (Fig. 3). Fertilized eggs were disinfected with 50 ppm argentine for 30-60 min during water hardening. Percent fertilization was measured at first picking during the 24-48 h immediately following fertilization. Eggs were incubated in the dark in an environmental control room at temperatures ranging from 6-8 C. Closed recirculation, vertical- flow (Heath stack) incubators were used with 1-5 percent replacement with groundwater daily (Fig. 4). Sac fry remained in incubators until approximately 80 percent of the yolk sac had been absorbed. Swim-up fry were placed in 370-L, 1.5-m diameter circular tanks (Fig. 5) until they reached 1 g. These fingerlings were then moved to 1800-L, 1.5-m diameter circular tanks until they reached 100-150 mm. Fry and fingerlings were grown under natural daylength at a water temperature of 10-17C. Tank water was recirculated through biofilters and approximately 1.8 L/min of groundwater was added continuously. Fish were grown in 3-m diameter, 7.5-m 3 tanks or 4-m diameter, A rctic char Salvelinus alpinus , the most northern of all freshwater fish, has a circumpolar distribution (Fig. 1, Scott and Crossman 1973). In cold temperate latitudes, Arctic char support significant fishery and aquaculture operations (Dumas et al . 1996). Currently more than half of all Arctic char aquaculture production occurs in Iceland, but this species is also commonly grown in other cold-temperate countries such as Canada, Sweden, Norway and Finland (Thorarinsdottir 2013). Demand for this premium- priced species exceeds supply (Delabbio 1995). Some strains of Arctic char and their hybrids have growth rates comparable to Kamloops rainbow trout reared in more southerly cold- temperate locations (Bebak- Williams 2001). Arctic char is cold-tolerant and adaptable to higher stocking densities, which makes them an ideal species for commercial production in colder climates (Thorarinsdottir 2013). However, although grow-out is exceptional at groundwater temperatures of 10-12C, production of viable gametes is marginal. The intrinsic temperature and light-cycle requirements of the Arctic char have caused commercial-scale production of seedstock to fail in south temperate latitudes (Thorarinsdottir 2013), even though groundwater temperatures are ideal for grow-out. Consequently, Arctic char eggs and fry are only available from a limited number of Canadian, Icelandic and Norwegian suppliers (Summerfelt et al . 2004). The northern half of the continental US has groundwater temperatures that support the grow-out of Arctic char (Fig. 2). However, to develop Arctic char aquaculture that takes advantage of optimal groundwater temperatures, a solution to the problems of Arctic char reproduction is needed. Hybrid Arctic Char Salvelinus alpinus × S. fontinalis : A New Aquaculture Candidate? John R. Foster, Brent C. Lehman and Lyndsay M. Burnette FIGURE 2. US groundwater temperatures (modified from Gass 1982). FIGURE 1. The circumpolar distribution of Arctic char. (Redrawn from Scott and Crossman 1973 and Lee et al. 1980).