Amago salmon Oncorhynchus masou ishikawae juveniles selectively bred for growth on a low fishmeal diet exhibit a good response to the low fishmeal diet due largely to an increased feed intake with a particular preference for the diet

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We have previously reported that amago salmon Oncorhynchus masou ishikawae juveniles selectively bred for growth on a low fishmeal diet exhibited superior growth performance on the low fishmeal diet compared to a control group fed the same diet. However, the physiological conditions as well as the growth and feed utilization of selected juveniles were inferior to juvenile replicates fed a fishmeal-based diet. In addition, since the selected juveniles showed improvements in feed intake for both diets relative to the counterparts of the control group, it was uncertain if the selected fish potentially had a particular preference for the low fishmeal diet. This study aimed to examine if further improvements in growth performance and physiological conditions occur in amago salmon selectively bred with a low fishmeal diet for three generations and if a selection with a fishmeal-based diet increases the acceptability of a low fishmeal diet. Juveniles (ca. 8gfish−1) of F3 amago salmon selectively bred on a low fishmeal diet (LFM-S), F3 amago salmon reared on a commercial fishmeal-based diet (FM-C) as a control, and F1 amago salmon selectively bred for growth on the fishmeal diet (FM-S), respectively, were fed either of an experimental fishmeal-based diet (FMD) or a low fishmeal diet (LFMD) for 10weeks. In LFM-S fed LFMD, 1.9 times higher weight gain (1.7 times higher in F2) was observed compared to FM-C fed LFMD. The feed efficiency ratio and feed consumption rate of LFM-S fed LFMD were also significantly higher (P<0.05) than FM-C fed LFMD. Although some improvements were observed in the hematological parameters and biliary bile acid status of LFM-S fed LFMD relative to FM-C fed LFMD, the physiological conditions as well as growth were still inferior to LFM-S fed FMD. In fish fed FMD, the growth and feed consumption of FM-S were similar to LFM-S and significantly higher than those of FM-C. By contrast, since the feed consumption of LFMD in FM-S did not increase significantly compared to FM-C, the growth of FM-S was only marginally improved relative to FM-C and inferior to LFM-S, all of which were fed LFMD. These results suggest that the superiority in growth of amago salmon selectively bred on a low fishmeal diet results from an increased feed intake with a particular preference for the diet. It is also indicated that another parental fish having physiological conditions resistant to soybean anti-nutritional factors should be introduced to the present amago salmon breeding. Statement of relevanceFish strain suitable for low fishmeal diets is demanded.