Lysine Requirement And Fish Meal Replament In Diets Of Tongue Sole, Cynolgossu Semilaevis Günther

Two feeding trials were conducted to investigate the optimum requirements of dietary lysine for tongue sole at three different growth stages (3.66g, 113.01g and 347.30g); the effect of dietary fish meal replacement by compound plant protein on growth performance, body composition and quality was also conducted. The results were summarized as follows:(1) Seven isonitrogenous (49.3% CP, DM) and isolipidic (21.7 KJ/g, DM) diets were formulated. Increasing levels of lysine were achieved by adding quantitative crystalline L-lysine·HCl at the expanse of glutamic acid and the lysine levels in the seven experimental diets were 1.19, 1.55, 1.91, 2.27, 2.63, 2.98 and 3.34%(DM), respectively. The juveniles (3.66±0.02g) were distributed at a density of 60 fish per aquarium (V=500L); the middle fish (113.01±0.88g) were distributed at a density of 19 fish per aquarium (V=500L); the adult fish (347.30±3.97g) were distributed at a density of 15 fish per aquarium (V=3000L). Each diet was randomly fed to triplicate groups of fish twice daily to satiation for 10 weeks. The results showed lysine deficient diets led to reduce growth and feed efficiency for tongue sole of three different growth stages. The optimum dietary lysine levels for tongue sole of three growth stages based on SGR were 2.85% (5.78% Pro), 2.49% (5.06% Pro) and 2.46% (4.99% Pro), respectively, which showed a decline tendency with increasing body weight. The optimum dietary lysine levels based on PR were 2.75% (5.58% Pro), 2.43% (4.92% Pro) and 2.58% (5.24% Pro), respectively. The optimum lysine intake of three growth stages based on protein gain was 22.63, 3.86 and 2.86mg.day-1, respectively. The optimum lysine intake based on PR was determined to be 22.00, 3.26 and 2.84mg.day-1, respectively.(2) Nine experimental diets were formulated to replace FM protein at the levels of 0, 20, 30, 40, 40, 40, 60 or 80% (designated as FM, PP20, PP30, PP40I, PP40II, PP40III, PP40IV, PP60 or PP80, respectively). Each diet was randomly assigned to triplicate groups of 15 fish (255.21±0.79g) per aquarium (500L). Fish were fed twice per day to apparent satiation for 9 weeks. The results showed that WG, SGR, FER, PER and PR were not significantly affected by the levels of the compound plant protein (P>0.05). Different compound plant protein levels had no significant effects on whole-body crude protein, moisture, Cu, Fe, Mg and P content in muscle (P>0.05). The whole-body crude lipid (CL) was negatively correlated with dietary compound plant protein levels, while ash was positively correlated with them (P<0.05). With the increasing of compound plant protein levels, cholesterol (CHO) in plasma decreased (r=0.966, P=0.002). Intestine structure of PP30, PP40I, PP40III, PP40IV and PP60 has a little damage, the lamina propria and the epithelium has quite a small amount of separation; intestine structure of PP80 was serious damaged, the lamina propria and the epithelium has quite a lot of separation. Some liver structure of PP80 was also abnormal, and the organization was disordered. Results of this study showed that 80% of fish meal can be replaced by the compound plant protein without affecting the survival, growth performance and feed efficiency.