Assessment of fish protein hydrolysate as a substitute for fish meal in white shrimp diets: Impact on growth, immune response, and resistance against Vibrio parahaemolyticus infection.

This study investigated the effects of fish protein hydrolysate derived from barramundi on growth performance, muscle composition, immune response, disease resistance, histology and gene expression in white shrimp (Penaeus vannamei). In vitro studies demonstrated FPH enhanced mRNA expressions of key immune-related genes and stimulated reactive oxygen species (ROS) production and phagocytic activity in shrimp hemocytes. To evaluate the effects of substituting fish meal with FPH in vivo, four isoproteic (43 %), isolipidic (6 %), and isoenergetic diets (489 kcal/100 g) were formulated with fish meal substitution levels of 0 % (control), 30 % (FPH30), 65 % (FPH65), and 100 % (FPH100). After 8-week feeding, the growth performance of FPH65 and FPH100 were significantly lower than that of control and FPH30 (p < 0.05). Similarly, the midgut histological examination revealed the wall thickness and villi height of FPH100 were significantly lower than those of control (p < 0.05). The shrimps were received the challenge of AHPND + Vibrio parahaemolyticus at week 4 and 8. All FPH-fed groups significantly enhanced resistance against Vibrio parahaemolyticus at week 4 (p < 0.05). However, this protective effect diminished after long-period feeding. No significant difference of survival rate was observed among all groups at week 8 (p > 0.05). The expressions of immune-related genes were analyzed at week 4 before and after challenge. In control group, V. parahaemolyticus significantly elevated SOD in hepatopancreas and Muc 19, trypsin, Midline-fas, and GPx in foregut (p < 0.05). Moreover, hepatopancreatic SOD of FPH65 and FPH100 were significantly higher than that of control before challenge (p < 0.05). Immune parameters were measured at week 8. Compared with control, the phagocytic index of FPH 30 was significantly higher (p < 0.05). However, dietary FPH did not alter ROS production, phenoloxidase activity, phagocytic rate, and total hemocyte count (p > 0.05). These findings suggest that FPH30 holds promise as a feed without adverse impacts on growth performance while enhancing the immunological response of white shrimp.

Effects of Replacing Fishmeal with Defatted Black Soldier Fly (Hermetia illucens Linnaeus) Larvae Meal in Japanese Eel (Anguilla japonica) Diet on Growth Performance, Fillet Texture, Serum Biochemical Parameters, and Intestinal Histomorphology.

An 8-week feeding trial was conducted to investigate the effects of replacing fishmeal with defatted black soldier fly larvae meal (DBSFLM) in the diets of Japanese eel on their growth performance, fillet texture, serum biochemical parameters, and intestinal histomorphology. Six isoproteic (520 g kg-1), isolipidic (80 g kg-1), and isoenergetic (15 MJ kg-1) diets were formulated with fishmeal replacement levels of 0% (R0), 15% (R15), 30% (R30), 45% (R45), 60% (R60), and 75% (R75). The growth performance, feed utilization efficiency, survival rate, serum liver function enzymes, antioxidant ability, and lysozyme activity of fish were not affected (P > 0.05) by DBSFLM. However, the crude protein and cohesiveness of the fillet in groups R60 and R75 significantly decreased, and the fillet hardness significantly increased (P < 0.05). Additionally, the intestinal villus length significantly decreased in the R75 group, and the goblet cell densities were significantly lower in the R45, R60, and R75 groups (P < 0.05). Overall, high levels of DBSFLM did not affect growth performance and serum biochemical parameters but significantly altered fillet proximate composition and texture and intestinal histomorphology (P < 0.05). The optimal fishmeal replacement level is 30% with 184 g kg-1 DBSFLM.

Rheum officinale extract promotes the innate immunity of orange-spotted grouper (Epinephelus coioides) and exerts strong bactericidal activity against six aquatic pathogens.

We investigated the antimicrobial properties and the effects of Rheum officinale extract (ROE) on nonspecific immune parameters of orange-spotted grouper (Epinephelus coioides) in vitro and in vivo. The in vitro analysis was conducted by treating grouper primary head kidney leukocytes with various concentrations of ROE. The phagocytic rate of the leukocytes was elevated in a dose-dependent manner from 0.01 to 0.1 mg/ml, but decreased with higher concentrations of ROE (0.5 and 1.0 mg/ml). The production of reactive oxygen species (ROS) was strongly enhanced in a dose-dependent manner by treatment with ROE doses of 0.1-10.0 mg/ml. However, morphological changes (e.g., rounding and shrinkage of cells, chromatin condensation, fragmentation, and appearance of apoptotic bodies) were observed in the leukocytes after incubation with higher concentrations of ROE (1.0 and 10.0 mg/ml). A 28-day feeding trial was performed to assess the impact of dietary administration of ROE on grouper innate immunity parameters. Fish were fed with feed supplemented with 0, 0.1, 1.0, or 5.0 g ROE per kg of feed. The phagocytic activity of the animals' leukocytes was significantly elevated in all ROE-fed groups on day 1 and in groups fed with ROE at 0.1 or 1.0 g/kg on day 14. Production of ROS was substantially increased on day 1 in fish fed with ROE at 1.0 and 5.0 g/kg, but decreased steadily later on. The ability to generate ROS increased steadily until day 7 in fish fed the lowest concentration of ROE (0.1 mg/ml), but decreased thereafter. ROE showed excellent antibacterial activity against six pathogens of aquatic animals: Vibrio parahaemolyticus, V. vulnificus, V. alginolyticus, V. carchariae, Aeromonas hydrophila, and Edwardsiella tarda. The minimum inhibitory and bactericidal concentrations of measured ROE-derived anthraquinones were 10.57-84.53 µg/ml and 10.57-169.05 µg/ml, respectively.