Gui-Ying Liang

Effect of Dietary Energy to Protein Ratios on Growth Performance and Feed Efficiency of Juvenile Grass Carp (Ctenopharyngodon idella)

A feeding trial of three dietary protein (DP) (25, 35 and 45%) and four dietary lipid (DL) levels (3, 6, 9 and 12%) with different dietary energy to protein (E/P) ratios (from 5.93 to 13.84 kcal/g protein) was conducted to investigate the proper dietary E/P ratio for juvenile grass carp. After acclimation of 2 weeks by a lipid-free diet, fish were reared for 10 weeks in a water recirculation system at 22.2 ± 2.8°C under natural light-dark cycle. The highest growth and feed effi- ciency were obtained with the diet of 45% DP and 3% DL (E/P ratio of 5.93 kcal/g protein), followed closely by the group with 35% DP and 3% DL (E/P ratio of 7.62 kcal/g protein), without any significant difference between them. At the same DP level, growth and feed efficiency decreased with increasing DL level. However, at the same DL level, growth and feed efficiency enhanced with increasing DP level. But at the 9% and 12% DL level (energy of 321 and 348 kcal/100g diet), there were no significant differences between groups in terms of growth indices, irrespective of the DP level. Except in- traperitoneal fat ratio, condition factor, viscera ratio and hepatosomatic index, all studied parameters showed increasing trends with enhancing dietary E/P ratio. Lipid contents of whole body and liver aroused with the increase of DL level at the same DP level. Taking into account the cost of feeding, the diet containing 35% DP and 3% DL (E/P ratio of 7.62 kcal/g protein, GE of 267 kcal/100g diet) is recognized as an optimal diet for juvenile grass carp in the present study. However, some future investigations will need to address the effects of temperature on optimal E/P ratio in grass carp.

The Intestinal Evacuation and Maximum Daily Consumption of Purified Formulated Diets by Juvenile Grass Carp (Ctenopharyngodon idella)

The intestinal evacuation and maximum daily consumption of two formulated diets with different lipid content (6 and 10%) was examined in juvenile grass carp at 28°C. Fish were fed formulated diets to satiety and removed at 1 hour interval for intestine weighing. The study showed that both diets were evacuated from intestine in 12h and the process of evacuation was expressed by linear regression. In the later study of maximum daily consumption, fish were fed formu- lated diets to satiety four times in a single day. The sum of diet consumption in the day was recorded. The experiment was repeated in 4, 7, 10, 13, 16, 19, 22 day by the same fish. The result showed the maximum daily consumption of two for- mulated diets is 3.64 ± 0.23 % body weight (416.79 ± 28.84 J/g.d -1 ) and 3.75 ± 0.16 % body weight (481.73 ± 19.44 J/g.d -1 ).

Effects of graded replacement of fish meal by fish protein hydrolysate on growth performance of early post-larval Pacific white shrimp (Litopenaeus vannamei, Boone)

Five dietary concentrations of fish protein hydrolysate (0, 9, 18, 27 and 36%) were included in five isonitrogenous diets (H0, H9, H18, H27 and H36) replacing fish meal by 0, 15, 30, 46 and 61% and offered to triplicate groups of early white shrimp post-larvae (mean initial wet weight 2 mg). After the 30-day feeding trial, the highest values of survival were obtained with shrimp fed diets H18 and H27. Final mean body wet weights (FBW, mg) of shrimp fed diets H9, H18, H27 and H36 were significantly higher than that of shrimp fed diet H0. Biomass gain (BG, g) of shrimp fed diets H18 and H27 were significantly higher than that of shrimp fed diets H0, H9 and H36. Specific growth rate (SGR, % day−1) showed the same pattern as FBW. Weight gain (WG, %) of shrimp fed diets H18 and H27 were significantly higher than that of shrimp fed diets H0 and H9. The trypsin activities of shrimp fed diets H9, H18, H27 and H36 were significantly higher than that of shrimp fed diet H0. Second-degree polynomial regression analysis on BG and WG indicated the appropriate supplement of fish protein hydrolysate in the diet of early white shrimp post-larvae should be between 21.22 and 26.35% of diet.

Excess dietary cholesterol may have an adverse effect on growth performance of early post-larval Litopenaeus vannamei

One experiment was conducted to determine the nutritive value of cholesterol for post-larval shrimp, Litopenaeus vannamei. Four isoenergetic and isonitrogenous diets supplemented with four levels of cholesterol (D1, D2, D3 and D4 with 0, 0.5%, 1% and 2% cholesterol, respectively) were fed to triplicate groups of L. vannamei shrimp (mean initial wet weight 0.8 mg) for 27 days. After the trial, shrimp fed the D1 diet had the best growth performance (final body weights: FBW; weight gain: WG; specific growth rate: SGR), while there was no significant difference between diet treatments with respect to survival. The whole body crude protein level in the shrimp decreased with the increase in dietary cholesterol levels, while the whole body crude lipid level in shrimps in the D4 diet treatment was significantly higher (P < 0.05) than in other diet treatments. Dietary analysis indicated that the D1 diet contained 0.92% cholesterol prior to supplementation, which may have satisfied the dietary cholesterol requirement of post-larval L. vannamei; excess dietary cholesterol may thus lead to adverse effects on the growth performance of post-larval shrimp.