Growth performance and macronutrient retention of offspring from wild and selected red sea bream (Pagrus major)

Two experiments were conducted to investigate nutritional trait differences between offspring from red sea bream selected for increased growth rate for four generations and offspring from wild-caught red sea bream. In experiment 1, juveniles (5.6 g, 30 fish/tank, triplicates) of both lines were fed low-lipid (17.1% lipid, 58.2% protein, by dry basis) or high-lipid (26.0% lipid, 52.4% protein by dry basis) diets by hand, twice daily to approximate satiation for 6 weeks. The selected line had higher feed intake (g/fish/6 weeks and %/wet biomass/day) and weight gain than the wild line, regardless of the dietary treatment. However, the selected line converted feed less efficiently than the wild line. The selected line had lower body protein content and body protein retention and higher body lipid content than the wild line, regardless of the dietary treatment. Body energy content (kJ/g) was higher in the selected line than in the wild line, though the energy retention was not significantly different between the lines. The selected line had higher visceral adipose mass and visceral adiposomatic index than the wild line. The dietary treatments affected feed intake, growth, feed efficiency and body protein retention. Significant interactions of line x diet were not found for any parameter. In experiment 2, fish (46 g in the selected line, 34 g in the wild line) from the same sources of experiment 1 were starved under resting or swimming condition for 14 days to compare protein and lipid expenditures. The selected line decreased body protein content during starvation under both conditions, while the protein content did not change in the wild line. Body lipid content decreased under swimming condition but not resting condition, irrespective of the lines. As overall traits, the selected line had higher feed intake and growth rate without improved feed efficiency, compared with the wild line. Moreover, the selected line seemed to consume protein rather than liquid as the energy source and have a higher ability to build fat deposits than the wild line.