Survival, growth and metabolic parameters of silver catfish, Rhamdia quelen, juveniles exposed to different waterborne nitrite levels

Nitrite Stress Induces Oxidative Stress and Leads to Muscle Quality Decreased in Wuchang Bream (Megalobrama amblycephala Yih) Juveniles

To determine the effects of nitrite exposure on muscle quality and physiological functions in Wuchang bream (Megalobrama amblycephala), we exposed M. amblycephala juveniles to acute nitrite (0, 1, 5, 10, 20 mg/L), and the muscle and blood samples were measured at 12, 24, 48, and 96 h. The results showed that when exposed to nitrite for 12 h, the concentrations of blood glucose, cortisol, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) in the 20 mg/L experimental group had the maximum value. The activity of lactate dehydrogenase (LDH) increased significantly in a dose-dependently manner and peaked at 96 h in the 20 mg/L group. During 96 h of exposure to nitrite, the total antioxidant capacity (T-AOC) and catalase (CAT) activity in the liver of the 20 mg/L experimental group were significantly higher than those of the control group, while the concentration of muscle glycogen showed a downtrend. At 12 h and 96 h, the hardness of the four experimental groups were significantly higher than that of the control group. Our research shows that acute sodium nitrite exposure will not only cause oxidative stress and decreased muscle quality in M. amblycephala juveniles but also will be accompanied by changes in serum biochemical index, liver antioxidant capacity, muscle physiological characteristics, and muscle physical characteristics. Preliminary speculation may be that acute nitrite exposure may cause M. amblycephala juveniles to choose to reduce muscle quality and activate antioxidant systems.

Organic and conventional agriculture: Conventional rice farming causes biochemical changes in Astyanax lacustris

World food production is directly related to human population growth. Chemicals are constantly applied to pest control in crops to increase productivity. Therefore, sustainable alternatives are needed to reduce environmental impacts. The biochemical responses in liver and muscle of Astyanax lacustris collected in different rice planting systems were analysed. Ten fish were collected in organic rice cultivation systems and conventional as well as water and sediment for pesticide analysis. In water from conventional system, bentazon (56.1 μg L^-1), fipronil (0.226 μg L^-1) and propoxur (0.141 μg L^-1) were found, while azoxystrobin and quinclorac were below the limit of quantification (LOQ). There were no pesticides in the sediment from the conventional system. In the water of the organic system, only propoxur (below the LOQ) was registered. Metalaxil (0.025 μg kg^-1) were verified in the sediment, while diphenoconazole, dinoxifene and tebuconazole were below the LOQ. The presence of these pesticides in crops with an organic production system may be related to proximity to crops to conventional production systems. Besides this, the amount is very low as compared with conventional system. Muscle glycogen, protein and amino acid levels were higher in fish collected in organic ponds. Lactate and ammonia levels were higher in conventional cultures. Lipids and proteins had greater oxidative damage in both tissues in the conventional system. Although pesticides were detected in organic sediments, the parameters of metabolic and oxidative damage were probably related by exposure to higher concentrations of pesticide in the water or by the lower oxygen content of conventional systems. However, fish mortality was not observed during collections. Despite being an anthropic environment, areas of organic cultivation seem to present better conditions for the survival of A. lacustris.

The effect of teprenone on the intestinal morphology and microbial community of Chinese sea bass (Lateolabrax maculatus) under intermittent hypoxic stress

Hypoxia stress may affect the fish intestine and thereby threaten the growth and survival of the fish. Teprenone is a clinically effective agent in protecting gastrointestinal mucosa. This study aims to assess the effect of teprenone in the intestine of Chinese sea bass Lateolabrax maculatus under intermittent hypoxic stress. L. maculatus juveniles were either raised under intermittent hypoxic condition or normal condition (NC). Part of the hypoxic-intervened fish were treated with teprenone at different concentrations (HTs), and the rest were regarded as hypoxic control (HC). Histological analysis was performed on the epithelial tissue of the fish intestine. High-throughput sequencing technology was used to analyze the diversity and composition of the microbial community in L. maculatus intestine. Reduced villi length and goblet cell, exfoliated enterocyte, and improper arrangement of villi were observed in HC compared with NC and HTs. Proteobacteria, Firmicutes, and Bacteroidetes represented the most abundant phyla in each sample. Significantly higher microbial diversity was detected in HC compared with NC (P < 0.05). At the phylum level, HC presented significantly decreased relative abundance of Proteobacteria, and significantly increased relative abundance of Bacteroidetes, Chloroflex, and Cyanobacteria compared with NC (P < 0.05). At the class level, HC showed significantly reduced relative abundance of Alphaproteobacteria and Bacilli, and significantly increased relative abundance of Clostridia, Gammaproteobacteria, and Bacteroides (P < 0.05). Teprenone protects the intestine from epithelial damages and maintains the microbial harmony in L. maculatus under intermittent hypoxic stress.

Mobilization of energetic substrates in the endangered catfish Steindachneridion parahybae (Siluriformes: Pimelodidae): changes in annual reproductive cycle in captivity

ABSTRACT This study aimed at analyzing the energetic substrate (ES) in the main storage tissues of Steindachneridion parahybae, throughout the reproductive cycle in captivity. Differently from wild, in captivity, feeding is not interrupted during the reproductive period, the females do not spawn spontaneously, and they are sedentary. Adult females were sampled monthly and based on their histology and gonadosomatic index (GSI), ovaries were classified into: previtellogenic (PRV), vitellogenic (VTG), and regression (REG) stages. Ovaries at the VTG stage showed higher protein and lipids levels than at the PRV stage with a positive correlation between these substrates and the GSI. Muscle was the main source of proteins transferred to the ovaries, according to the negative correlation between these organs. Lipids remained unchanged in the liver, which is an important supplier in vitellogenesis, a pattern that probably occurs due to the continuous feeding. Muscular glycogen levels were higher at the VTG and REG than at the PRV stages. Plasma triglycerides were also higher during REG, while glucose levels were more elevated during the VTG stage. These results suggest that with constant food supply, the pattern of deposition of ES in S. parahybae is different from that described for other wild potamodromous species.

Acute and chronic nitrite toxicity in juvenile pike-perch (Sander lucioperca) and its compensation by chloride

Pike-perch Sander lucioperca is currently considered as one of the most promising candidates for production in freshwater recirculation aquaculture systems (RAS). Here, due to the lack of studies on nitrite (NO(2)(-)) toxicity in pike-perch, a flow-through exposure at 0, 0.44, 0.88, 1.75, 3.5, 7, 14 and 28 mg/L NO(2)(-)-N was carried out to determine the acute and chronic toxicity over a period of 32 days. In juvenile pike-perch, 120 h LC(50) was 6.1mg/L NO(2)(-)-N and at ≥14 mg/L NO(2)(-)-N all fish had died within 24 h. Chronic exposure revealed a significant build up of NO(2)(-) in the plasma as well as in the muscles at ≥0.44 mg/L NO(2)(-)-N peaking in fish exposed to the highest concentration of 3.5 mg/L NO(2)(-)-N after 32 days. Still, due to high individual variation methemoglobin (MetHb) was only significantly increased (p<0.01) at 3.5 mg/L NO(2)(-)-N. No adverse effects on red blood cells (RBC) and hematocrit were observed in any of the treatments. In a second experiment, compensation of NO(2)(-) toxicity at increasing chloride concentrations (40 (freshwater), 65, 90, 140, 240, 440 mg/L Cl(-)) was observed at a constant exposure of 10 mg/L NO(2)(-)-N for 42 days. At ≥240 mg/L Cl(-), NO(2)(-) build-up in blood plasma and muscle was completely inhibited. At lower Cl(-) concentrations (≤140 mg/L), NO(2)(-) was significantly increased in plasma, but only insignificantly elevated in muscle due to high individual variation. MetHb was increased significantly difference only at 40 mg/L Cl(-) (freshwater control) compared to the control. Again, high individual variations were observed. As a conclusion, S. lucioperca is moderately sensitive towards NO(2)(-) and acceptable levels in RAS should hence not exceed 1.75 mg/L NO(2)(-)-N to avoid MetHb formation. However, based on the 120 h LC(50) and a factor of 0.01 according to Sprague (1971), a NO(2)(-) concentration of ≤0.061 mg/L NO(2)(-)-N is considered as "safe." Thereby, no NO(2)(-) should accumulate in the plasma or muscle tissue during chronic exposure. For 10 mg/L NO(2)(-)-N, ≥240 mg/L chloride compensates for NO(2)(-) uptake in plasma and muscle.