The rainbow trout (Oncorhynchus mykiss) is a key species for the European freshwater aquaculture with nearly 185,000 tons produced in 2020 (EUMOFA 2022). There are currently at least 7 selective breeding programs operating in Europe on this species. These programs have mainly been improving growth and slaughter traits, and some have been dealing with sexual maturity issues. The first results on the genetic basis of spawning performance date back to the 1970s. There is now a need to understand the genetic links between egg-production traits, growth performance and carcass quality traits.
Our experiment focused on 1600 females from a selected commercial line of rainbow trout (Aqualande, France). They were produced through partial factorial matings of 100 sires and 84 dams. The females were individually tagged and recorded for body weight (BW) at nine months of age (355 g), sixteen months of age (1700 g), twenty months of age (2600 g) and at spawning (2600 g, twenty-one months of age). Six periods of thermal growth coefficients (TGCs) were evaluated until spawning. The fat content in the fillet (Fat) was recorded three times, spawning included. The non-lethal predictor of carcass yield (PCY) was measured at sixteen and twenty months of age using ultrasound tomography. At spawning, the following traits were recorded: weight of the spawn (on average 342 g), number of eggs (~7100), weight of an egg (~48 mg), relative fecundity (~3300 eggs per kilogram of live female) and gonado-somatic index (~13%). The heritabilities and genetic correlations between TGCs, BWs, Fats, PCYs and spawning traits were estimated using linear animal models.
The genetic correlations between BWs and spawning traits were all either not different from zero or positive (depending on the trait, from 0.05 ± 0.12 to 0.70 ± 0.06), as for the TGCs (-0.20 ± 0.13 to 0.63 ± 0.07) and PCY at sixteen months of age (-0.03 ± 0.14 to 0.24 ± 0.14). On the contrary, PCY at twenty-months was genetically negatively correlated with egg-production traits (-0.16 ± 0.14 to -0.47 ± 0.11). The genetic correlations between the Fats and the spawning traits ranged from -0.20 ± 0.11 to 0.32 ± 0.10.
In this population, selecting for growth up to twenty months of age should not impact the spawning performance. It may even contribute to slightly enhance it. Improving the carcass yield should not impair the egg-production traits as long as the target age does not exceed twenty months. On the contrary, a selection pressure applied on carcass yield during the late period of the ovaries development may be detrimental. We did not evidence a clear impact on the evolution of Fat during rearing up to spawning. This may be due to the fact that the feed fulfills the requirements are highly enough respected for good egg production.
We recommend that in selective breeding programs of rainbow trout that do not target egg-production traits, there is some individual spawning performance follow-up. Indeed, this would enable to observe changes in the genetic correlations between traits and then adapt the index of selection, the pressures to be applied on the different traits of interest and at what age.
FranceAgriMer (National Institute for agricultural and sea products) and the European Marine and Fisheries Fund co-founded this work through the Best’Ov project (n°2014-0823). Authors thank warmly Marc Vandeputte and Mathilde Dupont-Nivet for useful brainstorming sessions.