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Study probes improving fillet yield in rainbow trout

Rainbow trout fillet yield may be improved by selective breeding. This process, however, poses a number of challenges. Researchers have noted, among other things, that it cannot be measured on live breeding candidates and its phenotypic variation is low.

A team in France worked with carcass and demonstrated that “residual headless gutted carcass weight (rHGCW) is heritable and highly genetically correlated to fillet yield in rainbow trout, and can be predicted by the ratio of abdominal wall thickness to depth of the peritoneal cavity (E8/E23), measured on live fish by ultrasound tomography.”

This was documented in a research article, First evidence of realized selection response on fillet yield in rainbow trout Oncorhynchus mykiss, using sib selection or based on correlated ultrasound measurements, by Mark Vendeputte, et al, and published in Frontiers in Genetics.

“In the present study, we performed divergent experimental selection for fillet yield in a rainbow trout population, comparing sib selection on residual headless carcass weight, indirect selection on E8/E23 measured on the candidates, and a combination of both. Parents were selected based on the two indices, and their offspring was evaluated for fillet yield and other morphological indices at 1.5 years of age, in order to evaluate realized selection response,” the study authors said.

It showed that offspring from groups Both+, rHGCW+ and E8/E23+ had a higher estimated breeding values (EBV) for rHGCW than the control group, while down-selected groups had a lower EBV.

EBVs are the value of an individual as a genetic parent. The lower the heritability of a trait under selection, the slower the herd will improve.

“Selection using sib information on rHGCW was on average more efficient than selection using the candidates’ own E8/E23 phenotypes, and downward selection (decreasing fillet%) was more efficient than upward selection,” they said.

This study on increasing fillet yield has been influenced by requirements in France for bigger fish. “In France, production historically moved from a vast majority of pan-size (250–350 g) trout to mostly large (>1 kg) and very large (>2.5 kg) trout aimed at production of fillet, which are consumed fresh or smoked. Thus, fillet yield has become an increasingly interesting trait for French fish breeders,” they explained.

There are more advantages to increased fillet yield other than catering to market preferences.

“Fillet yield, the proportion of edible fillet relative to body weight, is a major trait to improve in fish sold processed, as it has a direct impact on profitability and can simultaneously decrease the environmental impact of producing a given amount of fillet,” they said.