GROWTH AND MORTALITY OF DIPLOID AND TRIPLOID TIGER TROUT (SALMO-TRUTTAXSALVELINUS-FONTINALIS)

Size, growth rate and fry mortality were compared for diploids and triploids of three genetic types, brook trout and the two reciprocal tiger trout hybrids (Salmo trutta x Salvelinus fontinalis). Fry mortality was higher for triploids of all three genetic types compared with the corresponding diploids. Weights and fork lengths were recorded for three year classes at various times from 18 weeks to 38 months after fertilization. Triploids were approximately equal to diploids in size and growth rates at most ages for each genetic type, although triploid tiger trout tended to be slightly larger than their diploid sibs. Total biomass expected from 1000 fertilized eggs was higher for diploids compared with triploids for brook trout and the cross of brown trout females x brook trout males, but the reverse was true for the reciprocal cross. Overall, the brown trout female x brook trout male cross was superior to the reciprocal cross. Production of diploid tiger trout using brown females and brook males is worthwhile when sterile fish are desired.