The interactive effects of a gradual temperature decrease and long-term food deprivation on cardiac and hepatic blood flows in rainbow trout (Oncorhynchus mykiss)

Taurine efflux counters the hydrodynamic impact of anaerobic metabolism to protect cardiorespiratory function under acute thermal stress in brook char (Salvelinus fontinalis)

Upper thermal tolerance may be limited by convective oxygen transport in fish, but the mechanisms constraining heart function remain elusive. The activation of anaerobic metabolism imposes an osmotic stress on cardiomyocytes at high temperatures that must be countered to prevent swelling and cardiac dysfunction. We tested the hypothesis that cardiac taurine efflux is required to counter the osmotic impact of anaerobic end product accumulation in brook char, Salvelinus fontinalis. Fish were fed a diet enriched in β-alanine, a competitive inhibitor of the taurine transporter, to induce taurine deficiency and inhibit transporter function. In vivo, stroke volume increased by 60% and cardiac output doubled in control fish during a 2°C h-1 thermal ramp. Stroke volume was temperature insensitive in taurine-deficient (TD) fish, so cardiac output was 30% lower at high temperatures. The thermal sensitivity of aerobic metabolism did not differ, and lactate accumulated to a similar degree in the two diet treatment groups, indicating that taurine deficiency does not impact energy metabolism. Heart taurine efflux was absent and ventricular muscle osmolality was 40 mOsmol kg-1 higher in TD brook char following thermal stress. Swelling and decreased ventricular compliance likely impair diastolic filling to constrain stroke volume in TD fish. The adrenaline sensitivity of cardiac contractility and the regulation of intracellular pH in the brain and liver were also impacted in TD brook char. Taurine efflux appears necessary to counteract the hydrodynamic impact of activating anaerobic metabolism and this process may limit heart function under acute thermal stress.

Assessment of activity and heart rate as indicators for acute stress in Atlantic salmon

The aim of this study was to assess whether activity and heart rate sensor implants can be used to measure stress and thus estimate one important welfare indicator for fish in aquaculture pens, and if such measurements correlate to physiological factors measured through blood sampling. The experiment consisted of two parts: i) a bio-logger study where implanted sensors were used to monitor activity and heart rates for fish undergoing stress (crowding); and ii) an analysis of blood constituents (cortisol, glucose, lactate, and chloride) of a second group of fish undergoing the same treatment. We found that activity measurements can be used to track high-impact stress events but may not be suitable to discern possibly nuanced reactions to stress impacts of lower magnitude. While heart rate was measured reliably, e.g., in showing clear circadian rhythms, it was no credible proxy for predicting stress in this study. Our results thus underline challenges observed in previous work around the use of heart rate as stress indicator, and imply that the translation of its meaning into a proxy for stress needs further work. Although tag-based monitoring of stress is not without its difficulties, studies such as this provide a wealth of information on salmon behaviour and physiology, and the links between these.

Effects of starvation on the pharmacokinetics and optimal dosages of florfenicol and associated serum biochemistry in Asian seabass (Lates calcarifer)

Starvation has influence on physiology and pharmacokinetic (PK) characteristics of many drugs in land animals. However, similar PK information in fish is lacking. The current study examined the effects of starvation on fish PK, taking florfenicol (FF) in Asian seabass as an example. FF was orally administered at a single dose of 10 mg/kg into 35-day starved fish reared at 25 and 30°C and the serum FF concentration was analyzed by HPLC-FLD. At 30°C, the absorption and elimination half-lives of the starved fish were increased by 30% (from 0.44 to 0.57 h) and 55% (from 7.2 to 11.18 h), respectively. The volume of distribution, clearance, and area under the curve were changed from 1.25 to 0.71 L/kg, 0.120 to 0.044 L/kg/h, and 88 to 228 h·μg/ml, respectively. Similar starvation-induced PK changes were also observed at 25°C. The serum biochemical parameters, mainly the alanine aminotransferase, aspartate aminotransferase, and glucose levels, were significantly reduced in the starvation group. Overall, FF absorption, distribution, and elimination rates were reduced by starvation, resulting in four to five times lower optimal dosage than the non-starved fish. Drug treatment in starved fish should be treated with caution as overdosing and/or tissue residues could perceivably occur.

An updated review of cold shock and cold stress in fish

Temperature is critical in regulating virtually all biological functions in fish. Low temperature stress (cold shock/stress) is an often-overlooked challenge that many fish face as a result of both natural events and anthropogenic activities. In this study, we present an updated review of the cold shock literature based on a comprehensive literature search, following an initial review on the subject by M.R. Donaldson and colleagues, published in a 2008 volume of this journal. We focus on how knowledge on cold shock and fish has evolved over the past decade, describing advances in the understanding of the generalized stress response in fish under cold stress, what metrics may be used to quantify cold stress and what knowledge gaps remain to be addressed in future research. We also describe the relevance of cold shock as it pertains to environmental managers, policymakers and industry professionals, including practical applications of cold shock. Although substantial progress has been made in addressing some of the knowledge gaps identified a decade ago, other topics (e.g., population-level effects and interactions between primary, secondary and tertiary stress responses) have received little or no attention despite their significance to fish biology and thermal stress. Approaches using combinations of primary, secondary and tertiary stress responses are crucial as a research priority to better understand the mechanisms underlying cold shock responses, from short-term physiological changes to individual- and population-level effects, thereby providing researchers with better means of quantifying cold shock in laboratory and field settings.

Synthesis and evaluation of the HIF-1α inhibitory activity of 3(5)-substituted-4-(quinolin-4-yl)- and 4-(2-phenylpyridin-4-yl)pyrazoles as inhibitors of ALK5

The transcription factor hypoxia-inducible factor-1α (HIF-1α) plays an important role in apoptosis, metastasis, and proliferation and is recognized as an important potential therapeutic target for cancer. Six series of 3(5)-(6-methylpyridin-2-yl)-4-(quinolin-4-yl)pyrazoles (11a-d, 12a-d, and 18a-d) and 3(5)-(6-methylpyridin-2-yl)-4-(2-phenyl-pyridin-4-yl)pyrazoles (19a-d, 20a-d, and 21a-d) were synthesized and evaluated for activin receptor-like kinase 5 (ALK5) and HIF-1α inhibitory activity at the enzyme and cell levels. The effect of the lead compound 20d (J-1012) on HIF-1α activation in HCT116 cells was investigated. J-1012 markedly decreased the hypoxia-induced or TNF-induced accumulation of HIF-1α protein dose-dependently. Analysis revealed that J-1012 inhibited HIF-1α protein synthesis, without affecting the degradation of HIF-1α protein. Furthermore, by inhibiting the activation of HIF-1α, J-1012 suppressed the metastasis and proliferation and promoted apoptosis of HCT116 cells. These results suggest that J-1012 may be a potential therapeutic agent against human colon cancer.

Toxicokinetic models and related tools in environmental risk assessment of chemicals

Environmental risk assessment of chemicals for the protection of ecosystems integrity is a key regulatory and scientific research field which is undergoing constant development in modelling approaches and harmonisation with human risk assessment. This review focuses on state-of-the-art toxicokinetic tools and models that have been applied to terrestrial and aquatic species relevant to environmental risk assessment of chemicals. Both empirical and mechanistic toxicokinetic models are discussed using the results of extensive literature searches together with tools and software for their calibration and an overview of applications in environmental risk assessment. These include simple tools such as one-compartment models, multi-compartment models to physiologically-based toxicokinetic (PBTK) models, mostly available for aquatic species such as fish species and a number of chemical classes including plant protection products, metals, persistent organic pollutants, nanoparticles. Data gaps and further research needs are highlighted.

IPNV Antigen Uptake and Distribution in Atlantic Salmon Following Oral Administration

One impediment to the successful oral vaccination in fish is the hostile stomach environment that antigens must cross. Furthermore, uptake of antigens from the gut to systemic distribution is required for induction of systemic immunity, the dynamics of which are poorly understood. In the present study, groups of Atlantic salmon parr were intubated with live or inactivated infectious pancreatic necrosis virus (IPNV), either orally or anally. At 1, 24 and 72 h post infection (p.i.), the fish were sacrificed. Serum was used for assessing IPNV by ELISA, while formalin-fixed head-kidney, spleen, liver and intestine tissues were used for the demonstration of antigens by immunohistochemistry. Both live and inactivated IPNV antigens were observed in enterocytes of the intestines and in immune cells of the head-kidneys and spleens of all groups. In the liver, no antigens were observed in any of the groups. Significantly higher serum antigen OD values (p < 0.04) were observed in orally- compared to anally-intubated fish. By contrast, no difference (p = 0.05) was observed in tissue antigens between these groups by immunohistochemistry. No significant difference (p = 0.05) in serum antigens was observed between groups intubated with live and inactivated IPNV, while in tissues, significantly more antigens (p < 0.03) were observe in the latter compared to the former. These findings demonstrate that both live and inactivated IPNV are taken up by enterocytes in the intestines of Atlantic salmon, likely by receptor-mediated mechanisms. Higher IPNV uptake by the oral compared to anal route suggests that both the anterior and posterior intestines are important for the uptake of the virus and that IPNV is resistant to gastric degradation of the Atlantic salmon stomach.

Forced sustained swimming exercise at optimal speed enhances growth of juvenile yellowtail kingfish (Seriola lalandi)

Swimming exercise at optimal speed may optimize growth performance of yellowtail kingfish in a recirculating aquaculture system. Therefore, optimal swimming speeds (U_opt in m s⁻¹ or body lengths s⁻¹, BL s⁻¹) were assessed and then applied to determine the effects of long-term forced and sustained swimming at U_opt on growth performance of juvenile yellowtail kingfish. U_opt was quantified in Blazka-type swim-tunnels for 145, 206, and 311 mm juveniles resulting in values of: (1) 0.70 m s⁻¹ or 4.83 BL s⁻¹, (2) 0.82 m s⁻¹ or 3.25 BL s⁻¹, and (3) 0.85 m s⁻¹ or 2.73 BL s⁻¹. Combined with literature data from larger fish, a relation of U_opt (BL s⁻¹) = 234.07(BL)^−0.779 (R² = 0.9909) was established for this species. Yellowtail kingfish, either forced to perform sustained swimming exercise at an optimal speed of 2.46 BL s⁻¹ (“swimmers”) or allowed to perform spontaneous activity at low water flow (“resters”) in a newly designed 3600 L oval flume (with flow created by an impeller driven by an electric motor), were then compared. At the start of the experiment, ten fish were sampled representing the initial condition. After 18 days, swimmers (n = 23) showed a 92% greater increase in BL and 46% greater increase in BW as compared to resters (n = 23). As both groups were fed equal rations, feed conversion ratio (FCR) for swimmers was 1.21 vs. 1.74 for resters. Doppler ultrasound imaging showed a statistically significant higher blood flow (31%) in the ventral aorta of swimmers vs. resters (44 ± 3 vs. 34 ± 3 mL min⁻¹, respectively, under anesthesia). Thus, growth performance can be rapidly improved by optimal swimming, without larger feed investments.