Effects of Dietary Carbohydrate/Lipid Ratios on Growth, Feed Utilization, Hematology Parameters, and Intestinal Digestive Enzyme Activities of Juvenile Hybrid Grouper (Brown‐Marbled Grouper Epinephelus fuscoguttatus ♀ × Giant Grouper E. lanceolatus ♂)

Abstract

An 8‐week growth trial was conducted to investigate the effects of dietary carbohydrate (CHO)/lipid (L) ratios on growth, feed utilization, hematology parameters, and intestinal digestive enzyme activities of juvenile hybrid grouper (Brown‐marbled Grouper Epinephelus fuscoguttatus ♀ × Giant Grouper E. lanceolatus ♂). Seven isoproteic (53.5% dietary crude protein) and isoenergetic (3.6 kcal/g dry matter) experimental diets were formulated containing various CHO/L ratios: 0.03 (0.5% CHO/16% L); 0.36 (5% CHO/14% L); 0.79 (9.5% CHO/12% L); 1.4 (14% CHO/10% L); 2.31 (18.5% CHO/8% L); 3.83 (23% CHO/6% L); and 6.88 (27.5% CHO/4% L). Fifteen juvenile hybrid grouper (average initial body weight ± SE = 10.16 ± 0.16 g) were stocked in small floating cages. Triplicate groups of fish were fed each dietary treatment to apparent satiation twice daily (0800 and 1600 hours). Results showed that weight gain (WG; %), daily feed intake (DFI), feed conversion ratio (FCR), and protein efficiency ratio (PER) were significantly affected by different experimental diet treatments. Fish that were fed diets with CHO/L ratios of 3.83 and 6.88 had lower WG and PER but higher DFI and FCR than fish that received diets with other CHO/L ratios. Intraperitoneal fat ratio and whole‐body lipid content significantly decreased with increasing dietary CHO/L ratios. Hepatic glycogen content increased with increases in dietary digestible CHO level. Fish that received lower CHO/L ratios had lower plasma glucose concentrations than fish that were fed diets with higher CHO/L ratios. As dietary CHO/L ratio increased, intestinal lipase activity decreased, but intestinal α‐amylase activity increased. In conclusion, dietary energy from lipid could be partially replaced by that from digestible CHO without significant negative effects on growth performance of hybrid grouper. Furthermore, partial replacement of dietary lipid by CHO was beneficial for reducing fish adiposity through avoiding excessive lipid deposition in the abdominal cavity as well as in other tissues. We recommend 2.31 as a suitable dietary CHO/L ratio for hybrid grouper, since higher ratios (3.83 and 6.68) depressed fish growth performance.

Effects of Carbohydrase Supplementation on Growth Performance, Intestinal Digestive Enzymes and Flora, Glucose Metabolism Enzymes, and glut2 Gene Expression of Hybrid Grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) Fed Different CHO/L Ratio Diets

“…There were no significant differences in moisture, ash, and crude protein content between all treatment groups. In contrast, crude lipid decreased significantly with the increase in dietary CHO:L ratio, which was consistent with previous reported on large yellow croaker [ 28 ], hybrid Clarias catfish ( Clarias macrocephalus × C. gariepinus ) [ 36 ], and juvenile hybrid grouper [ 19 ]. When nutritional requirements are fulfilled, the appropriate lipid content in the diet is about 10% for hybrid grouper [ 37 ].…”

“…In order to maximize profits, diets are often formulated to contain high levels of CHO:L ratio to reduce feed costs. Although the optimal glycolipid ratio requirements at the juvenile stage of grouper have been studied [ 18 , 19 , 20 ], there is little research on the addition of carbohydrase based on different glycolipid ratios. With this in mind, the purpose of this study was to assess the influence of carbohydrase supplementation on growth performance, carbohydrate metabolic enzyme and glut2 gene expression in the Hybrid Grouper-fed diets with different CHO:L ratios.…”

Advances in practical feed formulation and adoption for hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) aquaculture

“…Alternative approaches include the use of modified starches that provide physical structure to compounded feed without resulting in excess liver glycogen deposition. 56 When compared on a balanced digestible energy basis, lipid is preferred over carbohydrate as an energy source for TGGG, with linearly decreased growth when lipid energy is replaced by starch energy 49,57 or starch increased at constant lipid levels. 49 Interestingly, the former finding was largely attributed to a lack of lipid rather than any negative attributes of excessive carbohydrates, whereas the latter study indicated that 8% starch is optimal and higher levels led to decreased growth.…”

“…33-35 c Lipid used to balance constant energy in feeds for different fish size, within the appropriate range reported. 38,39,49 d While apparently desirable to limit starch to this level, 49,57 Tryptophan Required-unknown quantitative requirement due to lack of data but are also required for optimal growth and health. 116,117 Both of these vitamins are present in significant quantities in fish oil, but at vastly variable concentrations, 118 and therefore, it is challenging to derive a likely contribution from raw materials in order to specify a premix addition.…”

“…Lecithin is often added to experimental feeds 50,57,63 with no explained purpose. Although lecithin is a source of choline, there are some indications that it may be important independently of its direct choline contribution 64 since it may support lipid emulsification and absorption.…”