FISHBOOST Results: Feed conversion ratio can be improved by selection for controlled lipid deposition

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By Milthon Lujan

FISHBOOST researchers have shown that prevention of excessive lipid deposition improves feed conversion ratio in rainbow trout. This also increases, yet slowly, the efficiency at which the fish utilizes proteins of feed (protein-retention efficiency), one of the most expensive and limited raw materials of the fish feeds.

Why is improving the feed conversion ratio so important?

Both feed conversion ratio (FCR) and protein-retention efficiency are two of the most economically important fish traits influencing profitability of aquaculture operations.

Feed incurs one of the largest costs in aquaculture production. Moreover, a fish can build proteins for tissues only from protein (amino acids) in feed, which makes it essential to use high-quality fish feeds. High-quality proteins are among the most expensive raw materials in an aqua feed formulation, and often of limited supply. Even a small improvement in protein-retention efficiency will have a large economic impact on the industry. Improved FCR also means that more feed is tied to fish biomass and hence less nutrients leak to the environment.

Selection for improved FCR

In farmed fish, selection for rapid growth is known to improve the efficiency in which fish use feed. Selection directly targeting the improvement of the FCR would be even more useful. To directly select for FCR, feed intake needs to be recorded, preferably from individual fish. However, fish are typically held in schools and are fed together, making the recording of feed intake of individual fish a major challenge.

Individually recorded feed intake or FCR is currently not selected in any fish breeding programme. One major goal in FISHBOOST is to find alternatives to recording individual feed intake. Lipid deposition is such a potential indicator trait of FCR, because in livestock lean animals are typically more efficient in converting feed to tissue growth compared to fat animals.

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Lipid deposition as indicator trait of FCR

The new FISHBOOST results show that genetic improvement of FCR can be enhanced by recording and selecting on lipid deposition, instead of recording feed intake. Replacing feed intake selection by selection on body lipid% may increase genetic response in FCR significantly up to 30%, compared to the sole selection for growth. Naturally, this is increase is not as high as the one obtained by recording and selecting directly on FCR or feed intake (50% increase in genetic response of FCR).

However, lipid deposition should not be reduced to an extreme because lipid is essential for fish reproduction, it is an important source of healthy fatty acids for humans, and lipid% of tissues may have an intermediate optimum for product quality.

It is reliable to use lipid deposition as a genetic indicator trait of FCR in a breeding programme since it has a known physiological relationship with FCR. The FISHBOOST results are in line with terrestrial farm animals in which leaner animals are typically more efficient.

Impact of FISHBOOST research

The FISHBOOST study contributes to the growing evidence that the control of excess lipid deposition by selective breeding improves not just feed conversion ratio, but also protein-retention efficiency in fish. An additional benefit of controlling lipid deposition is that lipid in different body parts influences both product quality and slaughter yield.

FISHBOOST researchers are currently validating recording tools to record lipid on live fish, without a need to sacrifice fish. This further improves the sustainability of aquaculture breeding operations and development work.

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The study was conducted in Tervo at the breeding nucleus of the Natural Resources Institute Finland (Luke).

Contact info: antti.kause@luke.fi
Project FISHBOOST: http://www.fishboost.eu

Kause A, Kiessling A, Martin SAM, Houlihan D & Ruohonen K. 2016. Genetic improvement of feed conversion ratio via indirect selection against lipid deposition in farmed rainbow trout (Oncorhynchus mykiss Walbaum). British Journal of Nutrition 116: 1656-1665. https://doi.org/10.1017/S0007114516003603

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