World Aquacluture Magazine - September 2020

WWW.WA S.ORG • WORLD AQUACULTURE • SEP TEMBER 2020 55 ( C O N T I N U E D O N P A G E 5 6 ) 15-m 3 tanks (Fig. 6). Tank water was recirculated through biofilters and approximately 3.8 L/min of groundwater was added to 3-m tanks and 7.6 L/min of groundwater was added to 4-m tanks. Grow-out occurred under natural photoperiod and temperatures ranging from 10-17C. Temperature and daylength manipulation initially resulted in a 30 percent fertilization rate for Fraser River Arctic char. After many generations of selection and years of technical refinements the fertilization rate increased to just over 60 percent. Although daylength and temperature manipulation combined with selection showed some success in fertilization rate, the egg hatching rate for pure-strain Arctic char remained dismal (Fig. 7). The feasibility of developing a strain of Arctic char that could reproduce at more southern latitudes through genetic selection and artificial daylength and temperature regimes did not look promising. Hybridization In the late 1990s, the focus shifted to examining the potential of interspecific hybridization. This strategy was largely based on natural hybridization between Arctic char and brook trout Salvelinus fontinalis in the Fraser River and elsewhere (Hammar et al. 1991). The thinking was that insertion of brook trout genes would increase the viability of hybrid Arctic char eggs at more southern latitudes. Thus, male Arctic char were crossed with female brook trout grown at SUNY (a cross between Ewing and NYSDEC domestic strain). The intention was to produce progeny that resembled Arctic char and that reproduced well under ambient conditions in NewYork State. If Arctic char hybrids can successfully reproduce at higher temperature and ambient light cycles, then they could become a viable aquaculture species in more southern locations. Arctic char typically spawn at a temperature of 4-7 C, but will continue to reproduce as low as 0 C (Brannas and Linner 2000). Brook trout have a more southern range than Arctic char, occurring from eastern Canada to the mountains of northeastern Georgia. Brook trout spawn at warmer temperatures than Arctic char, from 4.5-10 C (McAfee 1966). Both species spawn in the fall from September through November, depending on latitude. FIGURE 3. Dry spawning hybrid Arctic char. FIGURE 4. Recirculating, Heath stack, Arctic char egg incubators. FIGURE 5. Arctic char fry tanks (1.5-m diameter). FIGURE 6. The SUNY Cobleskill coldwater hatchery showing 3-m diameter grow-out tanks.