![]() ![]() Research was established to analyse daily feed intake and feed conversion ratio, a measure of feed efficiency, in 160 families over two spawning year classes. However, feed conversion efficiency is not currently a direct breeding goal. The family selective breeding programme operated by The New Zealand King Salmon Company has successfully improved growth and quality after six generations of selection. Improving performance through selective breeding is a key priority for the New Zealand Chinook salmon (Oncorhynchus tshawytscha) aquaculture industry. Scale stable isotope analyses are technically feasible and require further investigation. Metabolic rate might be useful as an indirect criterion if coupled with measures of ammonia excretion or body composition. Furthermore, fish should be phenotyped at holding conditions and feeding levels that are as close as possible to commercial practices. In particular, species collective behaviour must be considered when choosing the most suitable method. Phenotyping method for individual FE towards selective breeding depends, however, upon the species. Furthermore, I addressed methodological issues for implementation of stable isotope analyses with non-lethal sampling of fish scales as an indirect selection criterion.To conclude, selecting fish at juvenile stage seems reliable and will cut selection costs. In European sea bass, there was no correlation of individual FE with individual metabolic rate (as oxygen consumption). I therefore investigated potential indirect selection criteria that are easier to measure. Finally, I also found that the most efficient fish at restricted feeding were not the most efficient at satiety, in both species.Both phenotyping methods remain, however, tedious. Then, I compared the two phenotyping methods in Nile tilapia, to discover that they did not provide equivalent estimations. I demonstrated that estimating individual FE at juvenile stage in Nile tilapia was predictive of FE over the whole production cycle. The two best methods, to date, are either to rear fish individually or to tag them externally so that they can be visually identified while reared in small groups.I investigated some important issues related to estimation of individual FE, on two major aquaculture species, European sea bass Dicentrarchus labrax and Nile tilapia Oreochromis niloticus. ![]() This can be achieved by selective breeding but this requires methods for individual phenotyping, and measuring individual feed intake (FI) is technically challenging for fishes. Improving feed efficiency (FE) to produce the same amount of fish with less feed is a major objective for sustainable aquaculture. In finfish aquaculture, feed is expensive and has environmental impacts. This improves resource efficiency of aquaculture and reduces nutrient load to the environment. These results highlight that in breeding programmes of rainbow trout, control of lipid deposition improves not only FCR but also protein-retention efficiency. Both physiological and genetic mechanisms promote the hypothesis that low-lipid% fish are more efficient. Fish with genetically low body and muscle lipid% were more efficient in turning ingested protein into protein weight gain. Consequently, indirect selection for weight gain and against muscle lipid% was almost as effective as direct selection for FCR. Replacing feed intake in the selection index with body lipid%, muscle lipid% or viscera% increased genetic response in FCR by 1♲9-, 1♴9- and 1♰2-fold, respectively, compared with the sole selection for growth. The index theory calculations showed that simultaneous selection for weight gain and against feed intake (direct selection to improve FCR) increased the expected genetic response in FCR by 1♵0-fold compared with the sole selection for growth. A quantitative genetic analysis was used to quantify the benefit of replacing feed intake in a selection index with one of three lipid traits: body lipid%, muscle lipid% or viscera% weight of total body weight (reflecting visceral lipid). We tested the hypothesis that rainbow trout with low lipid% have genetically better FCR, and that lipid% may be genetically related to retention efficiency of macronutrients, making lipid% a useful indicator trait. In farmed fish, selective breeding for feed conversion ratio (FCR) may be possible via indirectly selecting for easily-measured indicator traits correlated with FCR. ![]()
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