Nitrogenous and phosphorus excretions in juvenile silver catfish (Rhamdia quelen) exposed to different water hardness, humic acid, and pH levels

Water Hardness Can Reduce the Accumulation and Oxidative Stress of Zinc in Goldfish, Carassius auratus

We investigated the changes in toxicity stress in goldfish, Carassius auratus, under exposure to different concentrations of Zn and water hardness for 14 days. We analyzed the changes in water hardness and Zn accumulation after exposure. To investigate the stress levels, the expression of metallothionein, caspase-3 activity, NO activity, and total antioxidant capacity were detected. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays were also performed to measure apoptosis in the liver. The results showed that compared to the control group, a more significant difference in the accumulation of Zn in body stress markers (metallothionein, caspase-3 activity, NO activity, and total antioxidant capacity) were observed with increasing Zn concentration and exposure time. Notably, at the same Zn concentration and exposure time, lower stress levels were discovered in the samples under harder water conditions. Finally, the TUNEL assay showed that Zn accumulation caused apoptosis and high water hardness could reduce the apoptosis. In conclusion, we found that high water hardness can influence the absorption of Zn, and alleviating the hardness levels can reduce the toxicity stress caused by Zn.

Acidified water impairs the lateral line system of zebrafish embryos

Acidification of freshwater ecosystems is recognized as a global environmental problem. However, the influence of acidic water on the early stages of freshwater fish is still unclear. This study focused on the sublethal effects of acidic water on the lateral line system of zebrafish embryos. Zebrafish embryos were exposed to water at different pH values (pH 4, 5, 7, 9, and 10) for 96 (0-96 h post-fertilization (hpf)) and 48 h (48∼96 hpf). The survival rate, body length, and heart rate significantly decreased in pH 4-exposed embryos during the 96-h incubation. The number of lateral-line neuromasts and the size of otic vesicles/otoliths also decreased in pH 4-exposed embryos subjected to 96- and 48-h incubations. The number of neuromasts decreased in pH 5-exposed embryos during the 96-h incubation. Alkaline water (pH 9 and 10) did not influence embryonic development but suppressed the hatching process. The mechanotransducer channel-mediated Ca²⁺ influx was measured to reveal the function of lateral line hair cells. The Ca²⁺ influx of hair cells decreased in pH 5-exposed embryos subjected to the 48-h incubation, and both the number and Ca²⁺ influx of hair cells had decreased in pH 5-exposed embryos after 96 h of incubation. In addition, the number and function of hair cells were suppressed in H⁺-ATPase- or GCM2-knockdown embryos, which partially lost the ability to secrete acid into the ambient water. In conclusion, this study suggests that lateral line hair cells are sensitive to an acidic environment, and freshwater acidification could be a threat to the early stages of fishes.

Metabolic and NH4 excretion rate of fresh water species, Chondrostoma regium in response to environmental stressors, different scenarios for temperature and pH

Changes in water temperature and pH levels have substantial adverse effects on aquatic organisms, hence causing physiological constraint on their well-being. To understand the physiological responses of Chondrostoma regium to temperature or pH changes, standard metabolic rate (SMR), maximum metabolic rate (MMR), absolute and factorial aerobic scope (AS&FAS) as well as the specific rate of ammonia excretion (J_amm) were measured at following temperatures: acute low (3.5-4.5 °C), 24 h low (5.5-6.5 °C), 7 d low (5.5-6.5 °C), acute high (30-31 °C), 24 h high (29-30 °C), 7 d high (28-29 °C), and different pH treatments: acute low (4.3-4.4), 24 h low (4.3-4.4), 7 d low (6.3-6.4), acute high (9.8-9.9), 24 h high (9.8-9.9), 7 d high (8.8-8.9). A control group was also assigned to optimum temperature = 22-23 °C and pH = 7.8-7.9. These experimental ranges for each treatment were obtained based on critical thermal and pH thresholds, i.e., 1.9 to 31.7 °C and 2.7 to 11.1, respectively. SMR was enhanced significantly (P < 0.05) following pH treatments, except for 24 h low pH treatment. Results showed significant (P < 0.05) changes in both SMR and MMR at low and high temperature treatments. The AS was elevated following pH treatments except for acute low pH treatment in which AS significantly was declined (P < 0.05). Low temperature treatments resulted in lower AS while no significant changes in AS were observed in high temperatures. In all treatments, FAS value did not differ significantly from control, except for acute and 24 h low treatments of both temperature and pH. All high pH and temperature treatments showed a significant increase (P < 0.05) in J_amm. Histopathological results of gills indicated hyperplasia and fusion of secondary lamella and kidneys histopathology revealed necrosis and loss of tubular lumen in the most treatments. Results indicated that increases in water temperature or pH are more stressful than the lower ranges of them, suggesting higher capability of fish to adjust to the low levels of temperature or pH.

Effects of water-borne copper and lead on metabolic and excretion rate of bahaii loach (Turcinoemacheilus bahaii)

Beyond the role of anthropogenic activities, natural sources of metal contaminations are still controversial, together counting, however, as a major threat to inland and coastal waters, becoming an even more prominent stressor for aquatic life. To address the effects of metals on the physiological response of fish, standard metabolic rate (SMR), maximum metabolic rate (MMR), aerobic scope (AS) and factorial aerobic scope (FAS) as well as specific rate of ammonia excretion (J_amm) of Turcinoemacheilus bahaii were determined following different water-borne Cu²⁺ and Pb²⁺ treatments. Following LC₅₀-96 h determination, 72 fish (BW = 1.153 ± 0.56 g and TL = 6.155 ± 0.97 cm) were exposed to different amounts of Cu²⁺ and Pb²⁺ in 9 different treatments (eight fish/treatment), including 0.910 mg l^-1 Cu²⁺ for 24 h, 0.455 mg l^-1 Cu²⁺ for 7d, 0.182 mg l^-1 Cu²⁺ for 14d and 0.091 mg l^-1 Cu²⁺ for 30 d as well as 124.430 mg l^-1 Pb²⁺ for 24 h, 62.215 mg l^-1 Pb²⁺ for 7d,12.443 mg l^-1 Pb²⁺ for 14d, 6.221 mg l^-1 Pb²⁺ for 30d and control. The SMR of fish was reduced following exposures to all Cu²⁺ and Pb²⁺ treatments (P < 0.05), except for 30d exposure as compared with the control. The MMR remained steady following all Cu²⁺ treatments while it was raised significantly (P < 0.05) following Pb²⁺ treatments at 7, 14 and 30d exposure. Although the AS showed a similar pattern to MMR, the FAS was elevated (P < 0.05) following all the treatments when compared with control. Lower J_amm were observed following all metals-treated fish in comparison with control (P < 0.05). In addition, higher (P < 0.05) levels of injuries were observed following all Cu²⁺ and Pb²⁺ treatments in gills and kidneys. The results suggest that Cu²⁺ and Pb²⁺ over the experimental period could impair the metabolic and excretory capacities, hence affecting the possible physiological performance of fish.

Degradation kinetics of organic chloramines and formation of disinfection by-products during chlorination of creatinine

Organic chloramines can interfere with the measurement of effective combined chlorine in chlorinated water and are potential intermediate products of highly toxic disinfection by-products (DBPs). In order to know more about the degradation and transformation of organic chloramines, a typical organic chloramine precursor creatinine was selected for investigation and a corresponding individual organic chloramine chlorocreatinine was prepared in this study. The preparation condition of chlorocreatinine by chlorination was established as chlorine/creatinine = 1 M/M, reaction time = 2 h and pH = 7.0. Then the degradation kinetics of chlorocreatinine during further chlorination was studied, and a second-order rate constant of 1.16 (±0.14) M^-1 s^-1 was obtained at pH 7.0. Solution pH significantly influenced the degradation rate, and the elementary rate constants of chlorocreatinine with HOCl+H⁺, HOCl, OCl^- and chlorocreatinine^- with OCl^- were calculated as 2.43 (±1.55) × 10⁴ M^-2 s^-1, 1.05 (±0.09) M^-1 s^-1, 2.86 (±0.30) M^-1 s^-1 and 3.09 (±0.24) M^-1 s^-1, respectively. Besides, it was found that chlorocreatinine could be further converted into several C-DBPs (chloroform and trichloroacetone) and N-DBPs (dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM)) during chlorination. The total yield of DBPs increased obviously with increasing pH, especially for TCNM. In addition, the presence of humic acid in creatinine solution could increase the formation of DCAN obviously during chlorination. Based on the UPLC-Q-TOF-MS analysis, the conversion pathways of chlorocreatinine were proposed. Several kinds of intermediate products were also identified as organic chloramines and some of them could even exist stably during the further chlorination.

The physiology of fish at low pH: the zebrafish as a model system

Ionic regulation and acid–base balance are fundamental to the physiology of vertebrates including fish. Acidification of freshwater ecosystems is recognized as a global environmental problem, and the physiological responses to acid exposure in a few fish species are well characterized. However, the underlying mechanisms promoting ionic and acid–base balance for most fish species that have been investigated remain unclear. Zebrafish (Danio rerio) has emerged as a powerful model system to elucidate the molecular basis of ionic and acid–base regulation. The utility of zebrafish is related to the ease with which it can be genetically manipulated, its suitability for state-of-the-art molecular and cellular approaches, and its tolerance to diverse environmental conditions. Recent studies have identified several key regulatory mechanisms enabling acclimation of zebrafish to acidic environments, including activation of the sodium/hydrogen exchanger (NHE) and H+-ATPase for acid secretion and Na+ uptake, cortisol-mediated regulation of transcellular and paracellular Na+ movements, and ionocyte proliferation controlled by specific cell-fate transcription factors. These integrated physiological responses ultimately contribute to ionic and acid–base homeostasis in zebrafish exposed to acidic water. In the present review, we provide an overview of the general effects of acid exposure on freshwater fish, the adaptive mechanisms promoting extreme acid tolerance in fishes native to acidic environments, and the mechanisms regulating ionic and acid–base balance during acid exposure in zebrafish.