Analysis of Acute Nitrite Exposure on Physiological Stress Response, Oxidative Stress, Gill Tissue Morphology and Immune Response of Large Yellow Croaker (Larimichthys crocea)

Accumulation and elimination properties and comparative toxicity of fluxapyroxad in juvenile and adult large yellow croaker (Larimichthys crocea)

Fluxapyroxad (FX), a succinate dehydrogenase inhibitor fungicide, has been detected in global marine and aquatic organisms. However, as a new pollutant, its biotoxicity and ecological risks to marine aquatic organisms are unclear. The accumulation and elimination processes and toxic effects of FX on Larimichthys crocea (L. crocea) at environmental concentrations were assessed. FX (1.0 μg/L) was rapidly enriched and persisted prolonged in L. crocea muscle and FX is highly toxic to juvenile L. crocea with the 96 h LC50 of 245.0 μg/L. Furthermore, the toxic effects of FX on juvenile L. crocea and adults L. crocea were compared and analyzed. In contrast to those of adult L. crocea, juvenile L. crocea showed a stronger oxidative stress response and rescued liver damage in terms of antioxidant enzyme activity, energy supply, and liver damage to FX. Transcriptomic analysis also showed that drug metabolism was activated. In the adult L. crocea, the disturbance of the energy metabolism, oxidative respiration, TCA cycle, and lipid metabolism genes were firstly found. The results revealed the accumulation and elimination pattern and ecotoxicological hazards of FX to L. crocea, which provided important theoretical basis for the study of environmental risks caused by new pollutants to marine organisms.

Study on the Adaptive Regulation of Light on the Stress Response of Mandarin Fish (Siniperca chuatsi) with Re-Feeding after Starvation

Light influences the stress response to environmental stimuli and feeding behaviors of Siniperca chuatsi and, thus, is an important regulator of normal growth and development. In this study, we first explored the important role of light on the digestive and stress capacity of S. chuatsi by studying the changes in physiological and biochemical indicators of S. chuatsi, taking the re-feeding after starvation as the constant environmental stimulus and the light intensity as the adjustable environmental stimulus. The activity of protease and lipase was generally higher in the stomach tissues than in the intestinal tissues, especially lipase, which was higher in stomach tissues under all light conditions, and the protease and lipase activity peaked in the stomach tissues of S. chuatsi at a light intensity of 18.44 ± 3.00 lx and in intestinal tissues at 11.15 ± 2.01 lx, respectively, indicating that greater light intensity increased the digestive capacity of stomach tissues, whereas lower light intensity facilitated the digestive capacity of intestinal tissues. The tissues of the gill, stomach, and intestine had relatively high activity of stress-related enzymes, whereas the tissues of the brain, kidney, liver, and plasma samples had relatively low activity of enzymes. Collectively, the results show that light intensity at 11.15 ± 2.01 lx promoted digestive capacity in the intestine and enhanced the anti-stress ability of S. chuatsi in response to stress induced by re-feeding after starvation. These findings should prove useful for artificial breeding of S. chuatsi.

Dietary High Glycinin Reduces Growth Performance and Impairs Liver and Intestinal Health Status of Orange-Spotted Grouper (Epinephelus coioides)

The aim of the study was to investigate whether the negative effects of dietary glycinin are linked to the structural integrity damage, apoptosis promotion and microbiota alteration in the intestine of orange-spotted grouper (Epinephelus coioides). The basal diet (FM diet) was formulated to contain 48% protein and 11% lipid. Fish meal was replaced by soybean meal (SBM) in FM diets to prepare the SBM diet. Two experimental diets were prepared, containing 4.5% and 10% glycinin in the FM diets (G-4.5 and G-10, respectively). Triplicate groups of 20 fish in each tank (initial weight: 8.01 ± 0.10 g) were fed the four diets across an 8 week growth trial period. Fish fed SBM diets had reduced growth rate, hepatosomatic index, liver total antioxidant capacity and GSH-Px activity, but elevated liver MDA content vs. FM diets. The G-4.5 exhibited maximum growth and the G-10 exhibited a comparable growth with that of the FM diet group. The SBM and G-10 diets down-regulated intestinal tight junction function genes (occludin, claudin-3 and ZO-1) and intestinal apoptosis genes (caspase-3, caspase-8, caspase-9, bcl-2 and bcl-xL), but elevated blood diamine oxidase activity, D-lactic acid and endotoxin contents related to intestinal mucosal permeability, as well as the number of intestinal apoptosis vs FM diets. The intestinal abundance of phylum Proteobacteria and genus Vibrio in SBM diets were higher than those in groups receiving other diets. As for the expression of intestinal inflammatory factor genes, in SBM and G-10 diets vs. FM diets, pro-inflammatory genes (TNF-α, IL-1β and IL-8) were up-regulated, but anti-inflammatory genes (TGF-β1 and IL-10) were down-regulated. The results indicate that dietary 10% glycinin rather than 4.5% glycinin could decrease hepatic antioxidant ability and destroy both the intestinal microbiota profile and morphological integrity through disrupting the tight junction structure of the intestine, increasing intestinal mucosal permeability and apoptosis. These results further trigger intestinal inflammatory reactions and even enteritis, ultimately leading to the poor growth of fish.