Influence of Herba Houttuyniae added to fodder on the morphological structure of the intestinal tract, the digestive enzymes, the intestinal flora, and immune function of koi carp (Cyprinus carpio) infected with Aeromonas veronii.

This study investigated whether adding Herba Houttuyniae to feed can improve intestinal function and prevent diseases for koi carp (Cyprinus carpio) infected with Aeromonas veronii. There was a total of 168 koi carp with an average body length of (9.43 ± 0.99) cm and an average body weight of (26.00 ± 11.40) g. The K group was the control group fed with basal feed, while the C group was fed with feed with a H. houttuyniae content of six per thousand. After 14 days of feeding, the fish were fasted for a day and then intraperitoneally injected with A. veronii for artificial infection, injection dose is 0.2 mL, and the concentration is 1 × 107 CFU/mL. Samples were collected from the two groups on days 0, 1, 2, and 4. The fold height, intestinal villus width, and muscle layer thickness in the gut of the koi carp were measured. In addition, on day 4, the activities of trypsin, α-amylase, and lipase in the gut were determined, and the intestinal flora of the carp in both groups was tested. The results showed that on the second and fourth days of sampling, the fold height and muscle layer thickness in the C group were significantly higher than those in the K group (P < 0.05). The villus width in the C group was slightly higher than that in the K group, but the difference was not significant (P > 0.05). Microscopic observation revealed that the intestinal structure of the carp in the C4 (day 4 in C group) group was more intact than that in the K4 (day 4 in K group) group. Moreover, the activities of trypsin, α-amylase, and lipase in the foregut and midgut in the C4 group were higher than those in the K4 group (P < 0.05). The activities of trypsin and α-amylase in the hindgut in the C4 group were higher than those in the K4 group (P < 0.05). Furthermore, beneficial bacteria, especially those in the genus Cetobacterium, were more abundant in the intestinal tract of the carp in the C4 group compared to the K group. In addition, comparisons and tests of IL-4 and IL-10 in the intestines of the fish in both groups demonstrated that the H. houttuyniae added to feed enhanced the immune function of the fish intestines after bacterial attack. In conclusion, for koi carp infected with A.veronii, adding H. houttuyniae to their feed not only improves the activity of digestive enzymes and the morphological structure of the intestine but also optimizes the beneficial intestinal microbiota, thereby protecting the intestinal tract.

The Circadian Rhythm of the Behavior and Gut Microbiota in Dybowski's Frogs (Rana dybowskii) during the Autumn Migration Period.

Many amphibian behaviors and physiological functions adapt to daily environmental changes through variations in circadian rhythms. However, these adaptations have yet to be reported in Dybowski's frog (Rana dybowskii). We aimed to elucidate the dynamic changes in the behavior and gut microbiota of R. dybowskii within a 24 h cycle during their migration to hibernation sites. Thus, we monitored their behavior at 4 h intervals and collected samples for microbiome analysis. We found that the juvenile frogs arrived at hibernation sites earlier than the adults. Among the adults, the male frogs arrived earlier. The richness and diversity of the gut microbiota in the adult R. dybowskii were lowest at 14:00. At 6:00, the differences between the males and females were most significant. At 18:00, there was an increase in the activity of Bacteroides, Coprobacillus, Ruminococcus, and Dorea in the intestinal tracts of the male frogs, whereas in the intestinal tract of the female frogs, there was an increase in the activity of Pseudoramibacter_Eubacterium, Desulfovibrio, Anaerotruncus, and PW3. This indicated diurnal rhythmic variations in the gut microbiota and significant sex-based differences in the microbial activity at different time points. Our findings contribute to the understanding of the circadian rhythm of R. dybowskii and provide crucial insights into improving breeding strategies.