Histological Changes Induced by Ammonia and pH on the Gills of Fresh Water Fish Cyprinus carpio var. communis (Linnaeus)

Effects of partial replacement of dietary flour meal with seaweed polysaccharides on the resistance to ammonia stress in the intestine of hybrid snakehead (Channa maculatus ♀ × Channa argus ♂)

The purpose of this study was to evaluate the effects of partial replacement of dietary flour meal with seaweed polysaccharides on survival rate, histology, intestinal oxidative stress levels, and expression of immune-related genes in hybrid snakeheads under acute ammonia stress. Four experimental diets were set: (C) basal diet with 0% of seaweed polysaccharides as the control group, (MR) basal diet with 10% of seaweed polysaccharides, (HR) basal diet with 15% of seaweed polysaccharides, (HF) basal diet with 10% of fish oil. After 60 days of feeding, fish fed with the diet of C group were sampled as the control group, and other fish were exposed to ammonia nitrogen for 48 h. Two concentrations of total ammonia nitrogen (TAN) were used in this study: 120 mg/L TAN (low concentration exposure group), and 1200 mg/L TAN (high concentration exposure group). After exposure to ammonia nitrogen for 48 h, fish were sampled. The results indicated that adding seaweed polysaccharides to the diet could improve the survival rate of hybrid snakeheads under high concentration of ammonia stress. Histopathological analysis demonstrated multiple abnormalities in gills and intestines after exposure to two concentrations of TAN. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and lactate dehydrogenase (LDH) were all increased in the MR group under two concentrations of TAN stress. The mRNA abundance of immune-related genes in fish intestinal tissues was significantly induced or inhibited. These results suggested that partial replacement of dietary flour meal with seaweed polysaccharides improved the ability of hybrid snakeheads to resist ammonia stress.

Sub-chronic exposure to ammonia inhibits the growth of juvenile Wuchang bream (Megalobrama amblycephala) mainly by downregulation of growth hormone/insulin-like growth factor axis

In this study, healthy Wuchang bream (Megalobrama amblycephala) juveniles were exposed to 0, 5, 10, 20 and 30 mg/L total ammonia nitrogen for 30 days to elucidate toxic effects and mechanisms of ammonia on growth performance involved with the regulation of growth hormone/insulin-like growth factor (GH/IGF) and hypothalamic-pituitary-thyroid (HPT) axes. Our results showed that the increasing total ammonia nitrogen concentrations caused dose-depend decreases in the weight gain and specific growth rate but increases in the food conversion ratio and mortality in juvenile bream, indicating growth inhibitory effects induced by ammonia. Concurrently, GH, IGF-1 at protein and mRNA levels were significantly decreased in ammonia exposure groups (p < .05), while serum thyroid stimulating hormone, free thyroxine, free triiodothyronine levels were significantly reduced only in fish exposed to higher concentrations of 20 and 30 mg/L ammonia (p < .05), suggesting that ammonia exposure could perturb both GH/IGF-axis and HPT-axis functions. Furthermore, transcriptional levels of extracellular regulated protein kinases 2 (erk2), phosphatidylinositol 3-kinase (pi3k), protein kinase B (akt), target of rapamycin (tom) and ribosomal protein S6 kinase-polypeptide 1(s6k1) in the dorsal muscle were significantly down-regulated in the fish exposed to ammonia (p < .05). This fact indicated that MAPK/ERK pathway and PI3K/AKT pathway should be responsible for the growth inhibition. Combining the results of spearman correlation coefficient, it should be noted that the GH/IGF axis played a more important role in regulating the growth than the HPT axis in Wuchang bream under persistent ammonia stress.