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Mitochondria exhibit suppressed ATP production, membrane potential (∆Ψ) polarization and reactive oxygen species (ROS) bursts during some cellular metabolic transitions. Although mitochondrial ROS release is influenced by ∆Ψ and respiratory state, the relationship between these properties remains controversial primarily because they have not been measured simultaneously. We developed a multiparametric method for probing mitochondrial function that allowed precise characterization of the temporal relationship between ROS, ∆Ψ and respiration. We uncovered a previously unknown spontaneous ROS spike - termed mitochondrial transition ROS spike (mTRS) - associated with re-polarization of ∆Ψ that occurs at the transition between mitochondrial energy states. Pharmacological inhibition of complex CI (CI), nicotinamide nucleotide transhydrogenase (NNT) and antioxidant system significantly decreased the ability of mitochondria to exhibit mTRS. NADH levels followed a similar trend to that of ROS during the mTRS, providing a link between CI and NNT in mTRS regulation. We show that (i) mTRS is enhanced by simultaneous activation of CI and complex II (CII); (ii) CI is the principal origin of mTRS; (iii) NNT regulates mTRS via NADH- and ∆Ψ-dependent mechanisms; (iv) mTRS is not a pH spike; and (v), mTRS changes in amplitude under stress conditions and its occurrence can be a signature of mitochondrial health. Collectively, we uncovered and characterized the biophysical properties and mechanisms of mTRS, and propose it as a potential diagnostic tool for CI-related dysfunctions, and as a biomarker of mitochondrial functional integrity.

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Naphthenic acids (NAs) are predominant compounds in oil sands influenced waters. These acids cause numerous acute and chronic effects in fishes. However, the mechanism of toxicity underlying these effects has not been fully elucidated. Due to their carboxylic acid moiety and the reported disruption of cellular bioenergetics by similar structures, we hypothesized that NAs would uncouple mitochondrial respiration with the resultant production of reactive oxygen species (ROS). Naphthenic acids were extracted and purified from 17-year-old oil sands tailings waters yielding an extract of 99% carboxylic acids with 90% fitting the classical O-NA definition. Mitochondria were isolated from rainbow trout liver and exposed to different concentrations of NAs. Mitochondrial respiration, membrane potential, and ROS emission were measured using the Oroboros fluorespirometry system. Additionally, mitochondrial ROS emission and membrane potential were evaluated with real-time flow cytometry. Results showed NAs uncoupled oxidative phosphorylation, inhibited respiration, and increased ROS emission. The effective concentration (EC) and inhibition concentration (IC) values for the end points measured ranged from 21.0 to 157.8 mg/L, concentrations similar to tailings waters. For the same end points, EC/IC values ranged from 11.8 to 66.7 mg/L, approaching concentrations found in the environment. These data unveil mechanisms underlying effects of NAs that may contribute to adverse effects on organisms in the environment.

Thirty six all male Oreochromis niloticus were divided into two groups, using six glass aquaria. The treated group was fed on a toxic strain of M. aeruginosa, while the control group was fed on a non toxic strain of M. aeruginosa, in order to measure their grazing rates from both strains of M. aeruginosa and consequently its effect on general fish health represented by, clinical signs, hematological changes and biochemical parameters. Grazing rates and daily intake of M. aeruginosa showed close grazing rates between the treated and the control groups with slightly higher intake of non toxic strain than the toxic one were the individual intake was 63,050 and 62,567 cell/ml/fish respectively. Clinical signs in O. niloticus associated with exposure to toxic cyanobacteria were investigated. The observed clinical signs were sluggish movement and reduced reflexes during the late stages of exposure period. Plasma glucose, cortisol, T4, creatinine and AST showed higher concentrations in the treated group than that in the control, indicating on increased fish stress that was reflected in its health state and consequently its performance. On the opposite side, plasma total protein concentration was higher in the control than that in treated group. The hematocrit, plasma albumin, LDH and Alkaline phosphatase concentrations did not show any significant difference in both groups. The study concluded that the uptake of toxic strain of M. aeruginosa via oral route had deleterious effects on some clinical and biochemical parameters of the blood of Nile tilapia which led finally affected the fish health. The study recommendations include prevention and monitoring of organic and inorganic pollution that promote the harmful algal blooms, and take the early preventive measures to avoid toxic effects of cyanobacteria on fish and consequently on humans.

Amyloodiniosis and vibriosis are serious diseases in European seabass ( Dicentrarchus labrax ) hatcheries with noticeable high mortality. This study was conducted on tank-cultured D. labrax frys at a private marine hatchery near Mariout Lake (Alexandria, Egypt). Frys showed a high mortality rate (70%), lethargy, darkening, asphyxia, ascites, and velvety skin appearance. Both infectious agents were presumptively identified in all investigated frys. The identities of the two recovered agents were confirmed by molecular assay and phylogenetic analysis. On the tissue level, histopathological examination of skin, splenic, and renal tissue indicated severe alterations due to the direct impacts of both infections. On the cellular level, scanning electron micrographs showed both protozoal and bacterial pathogens on/in gill epithelial cells in solitary and colonial forms. Vibrio alginolyticus showed variable results for tested antibiotics, with a higher sensitivity to florfenicol. A successful control strategy was strictly adopted to overcome infections and stop mortalities. Copper sulphate and hydrogen peroxide were efficiently applied to tank water to overcome A. ocellatum infections. Further, florfenicol was effectively used to overcome systemic V. alginolyticus infections. The efficacy of treatments was confirmed by the absence of infectious agents in randomly collected fish samples. To the best of the authors’ knowledge, this study is one of the earliest Egyptian studies that dealt with the dilemma of mass kills associated with external parasitic/systemic bacterial infections among hatchery-reared European seabass.