Inbreeding levels in selected populations of rainbow trout, Oncorhynchus mykiss

Inbreeding levels in three nucleus breeding populations of rainbow trout (Oncorhynchus mykiss) under selection for six generations were investigated. The inbreeding levels across generations as estimated from pedigree information (P-i) and effective population size (N-e) with the assumption of no selection and random mating, among the three populations were all at 11.3% or less. The levels of inbreeding estimated from N-e were generally lower than those calculated from P-i, except in the initial generations. The average rates of inbreeding (DeltaF) calculated from N-e and P-i were 0.99% and 2.00%, respectively, for population 1; 0.90% and 0.53%, for population 2; and 0.72% and 1.38%, for population 3. These rates of inbreeding correspond to N-e of 50 and 25, for population 1; 55 and 94, for population 2; and 70 and 36, for population 3. These rates were within the acceptable range 2% to 0.2%, corresponding to N-e of 31 to 250 for avoiding loss of fitness as suggested by Meuwissen and Woolliams [Meuwissen, T.H.E., Woolliams, J.A., 1994. Effective sizes of livestock populations to prevent a decline in fitness. Theor. Appl. Genet. 89, 1019-1026.]. A large proportion of individuals had inbreeding coefficients (F) greater than zero across generations for each population but the individual F were generally below 12.5%. The occurrence of inbreeding can be detrimental to populations undergoing artificial selection. Therefore, the F levels reported here should be followed-up by a study on the impact of inbreeding on important performance traits in rainbow trout. (C) 2001 Elsevier Science B.V. All rights reserved.