Effects of dietary protein
to energy ratios on growth and body composition of juvenile Japanese
seabass, Lateolabrax japonicus
Q. Ai, K. Mai, H. Li, Ch. Zhang,
L. Zhang, Q. Duan, B. Tan, W. Xu, H. Ma, W. Zhang, Z. Liufu-2004
Aquaculture,
230(1-4): 507-516
Abstract:
A growth experiment was conducted to determine the
optimal dietary protein to energy (P/E) ratio for juvenile Japanese seabass
(initial average weight 6.26±0.10 g). Nine practical diets were formulated
to contain three protein levels (36%, 41% and 46%), each with three lipid
levels (8%, 12% and 16%), in order to produce a range of P/E ratios (from
19.8 to 28.6 mg protein kJ-1). Each diet was randomly assigned to
triplicate groups of 60 fish in sea floating cages (1.5×1.5×2.0 m). Fish
were fed twice daily (06:30 and 16:30) to apparent satiation for 8 weeks.
The water temperature fluctuated from 26.5 to 32.5 °C, the salinity from 32
ppt to 36 ppt and dissolved oxygen content was approximately 7 mg l-1
during the experimental period. The results showed that the growth was
significantly affected by dietary P/E ratio (P<0.05). Fish fed the
diets with 46% protein (12% and 16% lipid, P/E ratio of 26.7 and 25.7 mg
protein kJ-1) had the highest specific growth rates (SGR) (4.26
and 4.24% day-1). However, fish fed the diet with 41% protein and
12% lipid showed comparable growth (4.20% day-1), and had higher
protein efficiency ratio (PER), protein productive value (PPV) and energy
retention than other groups (P<0.05). No significant differences
in survival were found among dietary treatments. Carcass lipid content
positively correlated with dietary lipid level irrespective of protein level
and inversely correlated with carcass moisture content. Carcass protein and
ash contents increased with increasing dietary lipid at each protein level.
These results suggest that the diet containing 41% protein and 12% lipid
with P/E of 25.9 mg protein kJ-1 is optimal for Japanese seabass.
(Key
Laboratory of Mariculture (Ministry of Education), Ocean University of
China, Qingdao 266003, PR China, e-mail of K. Mai: kmai@ouc.edu.cn)