Understanding the molecular mechanism of arsenic and ammonia toxicity and high-temperature stress in Pangasianodon hypophthalmus.

The current investigation explores the mechanisms of ammonia and arsenic toxicity, along with high-temperature stress, which other researchers rarely addressed. Pangasianodon hypophthalmus was exposed to low doses of ammonia and arsenic (1/10th of LC50, 2.0 and 2.68 mg L-1, respectively) and high temperature (34 °C) for 105 days. The following treatments were applied: control (unexposed), arsenic (As), ammonia (NH3), ammonia + arsenic (NH3 + As), ammonia + temperature (NH3 + T), and NH3 + As + T. Cortisol levels significantly increased with exposure to ammonia (NH3), arsenic (As), and high temperature (34 °C) compared to the unexposed group. Heat shock protein (HSP 70), inducible nitric oxide synthase (iNOS), and metallothionein (MT) gene expressions were notably upregulated by 122-210%, 98-122%, and 64-238%, respectively, compared to the control. Neurotransmitter enzymes (acetylcholine esterase, AChE) were significantly inhibited by NH3 + As + T, followed by other stressor groups. The apoptotic (caspase, Cas 3a and 3b) and detoxifying (cytochrome P450, CYP P450) pathways were substantially affected by the NH3 + As + T group. Immune (total immunoglobulin, Ig; tumor necrosis factor TNFα; and interleukin IL) and growth-related genes (growth hormone, GH; growth hormone regulator, GHR1 and GHRß; myostatin, MYST and somatostatin, SMT) were noticeably upregulated by NH3 + As + T, followed by other stress groups, compared to the control group. Weight gain %, protein efficiency ratio, feed efficiency ratio, specific growth rate, and other growth attributes were significantly affected by low doses of ammonia, arsenic, and high-temperature stress. Albumin, total protein, globulin, A:G ratio, and myeloperoxidase (MPO) were highly affected by the As + NH3 + T group. Blood profiling, including red blood cells (RBC), white blood count (WBC), and hemoglobin (Hb), were also impacted by stressor groups compared to the control group. Genotoxicity, as DNA damage, was significantly higher in groups exposed to NH3 + As + T (89%), NH3 + T (78%), NH3 (73), NH3 + As (71), and As (68%). The bioaccumulation of arsenic was substantially higher in liver and kidney tissues. The present study contributes to understanding the toxicity mechanisms of ammonia and arsenic, as well as high-temperature stress, through different gene expressions, biochemical attributes, genotoxicity, immunological status, and growth performance of P. hypophthalmus.

Multifunctional role of dietary copper to regulate stress-responsive gene for mitigation of multiple stresses in Pangasianodon hypophthalmus.

It is an urgent needs to address climate change and pollution in aquatic systems using suitable mitigation measures to avoid the aquatic animals' extinction. The vulnerability and extinction of the aquatic animals in the current scenario must be addressed to enhance safe fish food production. Taking into consideration of such issues in fisheries and aquaculture, an experiment was designed to mitigate high temperature (T) and low pH stress, as well as arsenic (As) pollution in fish using copper (Cu) containing diets. In the present investigation, the Cu-containing diets graded with 0, 4, 8, and 12 mg kg-1 were prepared and fed to Pangasianodon hypophthalmus reared under As, low pH, and high-temperature stress. The gene expression was highly affected in terms of the primary, secondary, and tertiary stress response, whereas supplementation of Cu-containing diet mitigates the stress response. Oxidative stress genes such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) were significantly upregulated by stressors (As, As + T, and As + pH + T). Whereas, heat shock protein (HSP 70), inducible nitric oxide synthase (iNOS), metallothionine (MT), caspase 3a (Cas 3a), and cytochrome P450 (CYP 450) were highly upregulated by stressors, while dietary Cu at 8 mg kg-1 diet significantly downregulated these gene expressions. Indeed, the immunity-related genes viz. TNFα, Ig, TLR, and immune-related attributes viz. albumin, globulin, total protein, A:G ratio, blood glucose, NBT, and myeloperoxidase (MPO) were also improved with Cu-containing diets. Cu containing diets substantially improved neurotransmitter enzyme (AChE) and vitamin C (Vit C). DNA damage was also reduced with supplementation of Cu at 8 mg kg-1 diet. The growth index viz. final body weight gain (%), specific growth rate, protein efficiency ratio, food conversion ratio, relative feed intake, and daily growth index were noticeably enhanced by Cu diets (4 and 8 mg kg-1 diet). The growth-related genes expressions viz. growth hormone (GH), growth hormone regulator 1 (Ghr1), growth hormone regulator ß (Ghrß,) myostatin (MYST), and somatostatin (SMT) supported the growth enhancement with Cu at 8 mg kg-1 diet. The bioaccumulation of As was reduced with Cu-containing diets. The fish were infected with Aeromonas hydrophila at the end of the 105 days experimental trial. Cu at 8 mg kg-1 diet improved immunity, reduced the cumulative mortality, and enhanced the relative percentage survival of the fish. The results revealed that the innovative Cu diets could reduce the extinction of the fish against climate change and pollution era and produce the safest production that is safe to humans for consumption.