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The Atlantic Salmon Broodstock Development Program is a partnership of researchers and producers that aims to breed salmon with an optimal combination of fast growth rate, low incidence of early sexual maturation, and good carcass quality for commercial aquaculture in Atlantic Canada. Estimation of genetic parameters for these traits is an essential step in the development of this breeding program. Four year classes of Atlantic salmon were produced, each consisting of 48–93 full-sib families. Marked fish from each of these families were randomly distributed to several producers to be raised under commercial conditions. At harvest, gutted body weights and sexual maturation level were observed in 812–3471 individuals per year class at processing plants. Additionally, colour score, astaxanthin, canthaxanthin, fat and moisture contents were recorded on 472 immature individuals from one year class. Genetic parameters were estimated with single- and multiple-trait animal models. Body weight, astaxanthin, canthaxanthin, colour, fat and moisture all exhibited moderate heritabilities (0.1–0.2), indicating that these traits should respond to selection. Positive genetic correlations were found between body weight and the carotenoid pigments, colour, and fat. These results indicate that direct selection for weight may have favourable indirect responses of higher colour scores and pigmentation but also an undesirable increase in flesh fat content. A properly weighted selection index should therefore be used to select broodstock for increased harvest weight and flesh colouration, while controlling flesh fat content.

Female spawn date was investigated in three diverse strains of rainbow trout (Oncorhynchus mykiss) and two year classes of complete diallel crosses between them. Spawn dates at 3 and 4 years of age were recorded for individual females in two generations. Spawn dates were analysed to find the effects of strain and year of maturation, and to estimate repeatability. Strains had significantly different spawning seasons, and hybrids generally performed intermediate to pure strains, with little evidence of heterosis. Some differences in performance occurred between reciprocal crosses such that hybrids spawned more like the strain of their dams. Four-year-old maiden females spawned approximately 18 days later than 4-year-old repeat spawning females. Spawn date repeatability estimates were 0.72 and 0.83. The second spawning season occurred 6 to 35 days earlier than the first season, depending on strain. Spawning time appears to be inherited in an additive manner, so it should be possible to predict future spawning dates based on past data and change spawning time through selection.

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 (Pi) and effective population size (Ne) 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 Ne were generally lower than those calculated from Pi, except in the initial generations. The average rates of inbreeding (ΔF) calculated from Ne and Pi 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 Ne 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 Ne 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.

Three nucleus breeding populations of rainbow trout (Oncorhynchus mykiss) under selection for six generations were investigated for the effect of inbreeding on body weight at harvest. The coefficients of inbreeding for each individual were estimated from complete pedigree information starting at base generation zero. For each population within generation, inbreeding effect was estimated using a fixed linear model and a sire–dam mixed additive genetic model. Estimates of inbreeding effect per generation vary due to the different distributions of inbreeding coefficients in each generation. The magnitude of inbreeding effect for each population across generations were estimated using a fixed linear model and three sire–dam mixed models: additive (A), additive plus dominance (A+D), and additive plus dominance plus additive by additive epistasis (A+D+A×A) with the inbreeding coefficient, F as covariate. The estimates of inbreeding effect from the fixed linear model were substantially lower than those from the sire–dam mixed models for all populations. The models (A+D) and (A+D+A×A) exhibited quite similar estimates of inbreeding effect, which were substantially higher than the (A) model. The results suggest that addition of the additive by additive genetic effect in the (A+D) model does not have a significant outcome on the estimation of inbreeding effect because additive by additive genetic interaction may not be important for growth. For unbiased estimation of inbreeding effect, the (A+D) model with F as a covariate may be sufficient. The inbreeding effect on body weight at harvest calculated as the average of the estimates obtained from models A+D and A+D+A×A, were −1.6, −5.0, and –4.5% per 10% unit increase in inbreeding coefficients for populations 1, 2, and 3, respectively. These values meant body weight at harvest was moderately affected by inbreeding but were not high enough to cause any serious impact in the selective breeding program for rainbow trout in Norway. This implies that maintenance of moderate effective population size per generation and following a strict mating policy for breeders selected as parents for future generations could delay the accumulation of inbreeding and minimize its effect on growth.

Comparisons of growth for diploid and triploid full sibs from 20 families of Atlantic salmon (Salmo salar L.), ranging from 4 to 24 progeny/family, involved 628 individuals. Length and weight data, after approximately 75 weeks in seawater, indicated higher within and between family variances in triploids than in diploids. Regression analyses revealed that improvement of triploid populations might require measurements on triploid sibs of the diploid to be involved in reproduction.

Uneyed-egg, eyed-egg and alevin mortalities were compared for 750 diploid families of brook trout ( Salvelinus fontinalis ), brown trout ( Salmo trutta ) and their reciprocal hybrids, known as tiger trout, produced over 4 years. The reciprocal tiger trout crosses experienced higher overall mortality than either pure species. The brook female × brown male cross experienced high mortality at all three stages examined, while the reciprocal cross experienced heavy losses only at the alevin stage, resulting in higher overall survival rates. Within the brook female × brown male cross, females were the most important source of variation for all types of mortality, but brown males were also an important source of variation for uneyed-egg mortality. In the reciprocal cross, male and female parents were both important sources of variation for alevin mortality, the major source of early mortality in this cross. For brook trout female parents, hybrid offspring mortality was not significantly correlated with mortality among pure brook trout offspring. Similarly, mortality of hybrid offspring of brown trout dams was not correlated with mortality of brown trout offspring except at the eyed-egg stage, a rather unimportant source of mortality in this cross. The influence of triploid induction on survival rates among brook trout and tiger trout families was studied by comparing diploid and triploid full sibs over 87 pairs of families. In general, triploid induction improved the survival rates of tiger trout at the alevin stage, but reduced survival at the uneyed-egg stage, so that overall survival was not greatly improved. Thus, early survival of tiger trout can be maximized by the use of the brown female × brook male cross, and by selection of the females and the brook males based on the survival rates among their hybrid offspring. The usefulness of triploid induction in the production of tiger trout will depend on modification of the induction techniques so that mortality from the induction is minimized.