Morphology and cardiac physiology are differentially affected by temperature in developing larvae of the marine fish mahi-mahi (Coryphaena hippurus)

Effects of exposure to sediment-associated fipronil on cardiac function of Neotropical armored catfish Hypostomus regani

Fipronil is widely used as a broad-spectrum insecticide in agriculture, urban environments, and veterinary medicine. Fipronil can enter aquatic ecosystems and spread to sediment and organic matter, representing a risk to non-target species. This study aimed to evaluate the effects of short-term (96 h) exposure to a low and realistic concentration of sediment-associated fipronil (4.2 µg.kg^-1 of Regent® 800 WG) on myocardial contractility of armored catfish Hypostomus regain, a benthic fish species. Fipronil exposure induced increased inotropism and acceleration of contractile kinetics, although no alterations in the relative ventricular mass were observed. This better cardiac function was associated with an elevated expression and/or function of the Na⁺/Ca²⁺ exchanger and its marked contribution to contraction and relaxation, probably due to a stress-induced adrenergic stimulation. Ventricle strips of exposed fish also exhibited a faster relaxation and a higher cardiac pumping capacity, indicating that armored catfish were able to perform cardiac adjustments to face the exposure. However, a high energetic cost to maintain an increased cardiac performance can make fish more susceptible to other stressors, impairing developmental processes and/or survival. These findings highlight the need for regulations of emerging contaminants, such as fipronil, to ensure adequate protection of the aquatic system.

Risk of chlorine dioxide as emerging contaminant during SARS-CoV-2 pandemic: enzyme, cardiac, and behavior effects on amphibian tadpoles

Objective

The use of chlorine dioxide (ClO₂) increased in the last year to prevent SARS-CoV-2 infection due to its use as disinfectant and therapeutic human treatments against viral infections. The absence of toxicological studies and sanitary regulation of this contaminant represents a serious threat to human and environmental health worldwide. The aim of this study was to evaluate the acute toxicity and sublethal effects of ClO₂ on tadpoles of Trachycephalus typhonius, which is a common bioindicator species of contamination from aquatic ecosystems.

Materials and methods

Median lethal concentration (LC50), the lowest-observed effect concentration (LOEC), and the no-observed effect concentration (NOEC) were performed. Acetylcholinesterase (AChE) and glutathione-S-transferase (GST) activities, swimming behavior parameters, and cardiac rhythm were estimated on tadpoles of concentrations ≤ LOEC exposed at 24 and 96 h. ANOVA and Dunnett’s post-hoc comparisons were performed to define treatments significance (p ≤ 0.05).

Results

The LC50 of ClO₂ was 4.17 mg L⁻¹ (confidence limits: 3.73–4.66). In addition, NOEC and LOEC values were 1.56 and 3.12 mg L⁻¹ ClO₂, respectively, at 48 h. AChE and GST activities, swimming parameters, and heart rates increased in sublethal exposure of ClO₂ (0.78–1.56 mg L⁻¹) at 24 h. However, both enzyme activities and swimming parameters decreased, whereas heart rates increased at 96 h.

Conclusion

Overall, this study determined that sublethal concentrations of ClO₂ produced alterations on antioxidant systems, neurotoxicity reflected on swimming performances, and variations in cardiac rhythm on treated tadpoles. Thus, our findings highlighted the need for urgent monitoring of this chemical in the aquatic ecosystems.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13530-021-00116-3.

Field assessments of heart rate dynamics during spawning migration of wild and hatchery-reared Chinook salmon

During spawning, adult Pacific salmonids (Oncorhynchus spp.) complete challenging upriver migrations during which energy and oxygen delivery must be partitioned into activities such as locomotion, maturation and spawning behaviours under the constraints of an individual's cardiac capacity. To advance our understanding of cardiac function in free-swimming fishes, we implanted migrating adult Chinook salmon (Oncorhynchus tshawytscha) collected near the mouth of the Sydenham River, Ontario, with heart rate (f_H) biologgers that recorded f_H every 3 min until these semelparous fish expired on spawning grounds several days later. Fundamental aspects of cardiac function were quantified, including resting, routine and maximum f_H, as well as scope for f_H (maximum-resting f_H). Predictors of f_H were explored using generalized least-squares regression, including water temperature, discharge, fish size and fish origin (wild versus hatchery). Heart rate was positively correlated with water temperature, which aligned closely with daily and seasonal shifts. Wild fish had slower resting heart rates than hatchery fish, which led to significantly higher scope for f_H. Our findings suggest that wild salmon may have better cardiac capacity during migration than hatchery fish, potentially promoting migration success in wild fish. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

Combined Effects of Elevated Temperature and Crude Oil Pollution on Oxidative Stress and Apoptosis in Sea Cucumber (Apostichopus japonicus, Selenka)

Currently, global climate change and oil pollution are two main environmental concerns for sea cucumber (Apostichopus japonicus) aquaculture. However, no study has been conducted on the combined effects of elevated temperature and oil pollution on sea cucumber. Therefore, in the present study, we treated sea cucumber with elevated temperature (26 °C) alone, water-accommodated fractions (WAF) of Oman crude oil at an optimal temperature of 16 °C, and Oman crude oil WAF at an elevated temperature of 26 °C for 24 h. Results showed that reactive oxygen species (ROS) level and total antioxidant capacity in WAF at 26 °C treatment were higher than that in WAF at 16 °C treatment, as evidenced by 6.03- and 1.31-fold-higher values, respectively. Oxidative damage assessments manifested that WAF at 26 °C treatment caused much severer oxidative damage of the biomacromolecules (including DNA, proteins, and lipids) than 26 °C or WAF at 16 °C treatments did. Moreover, compared to 26 °C or WAF at 16 °C treatments, WAF at 26 °C treatment induced a significant increase in cellular apoptosis by detecting the caspase-3 activity. Our results revealed that co-exposure to elevated temperature and crude oil could simulate higher ROS levels and subsequently cause much severer oxidative damage and cellular apoptosis than crude oil alone on sea cucumber.

What do warming waters mean for fish physiology and fisheries?

Environmental signals act primarily on physiological systems, which then influence higher-level functions such as movement patterns and population dynamics. Increases in average temperature and temperature variability associated with global climate change are likely to have strong effects on fish physiology and thereby on populations and fisheries. Here we review the principal mechanisms that transduce temperature signals and the physiological responses to those signals in fish. Temperature has a direct, thermodynamic effect on biochemical reaction rates. Nonetheless, plastic responses to longer-term thermal signals mean that fishes can modulate their acute thermal responses to compensate at least partially for thermodynamic effects. Energetics are particularly relevant for growth and movement, and therefore for fisheries, and temperature can have pronounced effects on energy metabolism. All energy (ATP) production is ultimately linked to mitochondria, and temperature has pronounced effects on mitochondrial efficiency and maximal capacities. Mitochondria are dependent on oxygen as the ultimate electron acceptor so that cardiovascular function and oxygen delivery link environmental inputs with energy metabolism. Growth efficiency, that is the conversion of food into tissue, changes with temperature, and there are indications that warmer water leads to decreased conversion efficiencies. Moreover, movement and migration of fish relies on muscle function, which is partially dependent on ATP production but also on intracellular calcium cycling within the myocyte. Neuroendocrine processes link environmental signals to regulated responses at the level of different tissues, including muscle. These physiological processes within individuals can scale up to population responses to climate change. A mechanistic understanding of thermal responses is essential to predict the vulnerability of species and populations to climate change.

Seabream Larval Physiology under Ocean Warming and Acidification

The vulnerability of early fish stages represents a critical bottleneck for fish recruitment; therefore, it is essential to understand how climate change affects their physiology for more sustainable management of fisheries. Here, we investigated the effects of warming (OW; +4 °C) and acidification (OA; ΔpH = 0.5) on the heart and oxygen consumption rates, metabolic enzymatic machinery—namely citrate synthase (CS), lactate dehydrogenase (LDH), and ß-hydroxyacyl CoA dehydrogenase (HOAD), of seabream (Sparus aurata) larvae (fifteen days after hatch). Oxygen consumption and heart rates showed a significant increase with rising temperature, but decreased with pCO2. Results revealed a significant increase of LDH activity with OW and a significant decrease of the aerobic potential (CS and HOAD activity) of larvae with OA. In contrast, under OA, the activity levels of the enzyme LDH and the LDH:CS ratio indicated an enhancement of anaerobic pathways. Although such a short-term metabolic strategy may eventually sustain the basic costs of maintenance, it might not be adequate under the future chronic ocean conditions. Given that the potential for adaptation to new forthcoming conditions is yet experimentally unaccounted for this species, future research is essential to accurately predict the physiological performance of this commercially important species under future ocean conditions.

Biotoxicity of diclofenac on two larval amphibians: Assessment of development, growth, cardiac function and rhythm, behavior and antioxidant system

The non-steroidal anti-inflammatory drug diclofenac (DCF) threatens the health of aquatic animals and ecosystems. In the present study, different biological endpoints (mortality, development and growth, abnormalities, cardiotoxicity, neurotoxicity and antioxidant system) were used to characterize the acute and chronic effects of DCF (at concentrations ranging between 125 and 4000 μg L^-1) on two amphibian species from Argentina (Trachycephalus typhonius and Physalaemus albonotatus). Results showed that the larval developmental, growth rates, and body condition of DCF-exposed individuals of both species were significantly reduced. DCF-exposed individuals also showed several morphological abnormalities, including significantly altered body axis, chondrocranium and hyobranchial skeleton, and organ and visceral abnormalities including cardiac hypoplasia, malrotated guts, asymmetrically inverted guts, and cholecystitis. DCF also had a significant effect on the swimming performance of both species: at low concentrations (125 and 250 μg L^-1), swimming distance, velocity and global activity decreased, whereas, at high concentrations (1000 and 2000 μg L^-1), these behavioral responses increased. Regarding cardiac function and rhythm, at DCF concentrations higher than 1000 μg L^-1, the heart frequency and ventricular systole interval of both species were significantly reduced. Regarding the antioxidant system, the activity of acetylcholinesterase indicated that DCF is neurotoxic and thus related to the changes in behavioral performance. The DCF concentrations studied produced a biochemical imbalance between radical oxygen species production and antioxidant systems. The sensitivities to sublethal and chronic DCF exposure in both anuran species were similar, thus indicating the inherent complexity involved in understanding the biotoxic effects of DCF.

Mahi-mahi (Coryphaena hippurus) life development: morphological, physiological, behavioral and molecular phenotypes

Background

Mahi‐mahi (Coryphaena hippurus) is a commercially and ecologically important fish species that is widely distributed in tropical and subtropical waters. Biological attributes and reproductive capacities of mahi‐mahi make it a tractable model for experimental studies. In this study, life development of cultured mahi‐mahi from the zygote stage to adult has been described.

Results

A comprehensive developmental table has been created reporting development as primarily detailed observations of morphology. Additionally, physiological, behavioral, and molecular landmarks have been described to significantly contribute in the understanding of mahi life development.

Conclusion

Remarkably, despite the vast difference in adult size, many developmental landmarks of mahi map quite closely onto the development and growth of Zebrafish and other warm‐water, active Teleost fishes.

Mahi‐mahi is a tractable model for experimental studies high‐performance pelagic predatory fish species.

Biological attributes of mahi are reported in a comprehensive developmental table.

Physiological, behavioral and molecular landmarks are described through the life development.

Mahi has a rapid growth rate, but the developmental marks are similar to other teleost fishes.

Insecticide pyriproxyfen (Dragón®) damage biotransformation, thyroid hormones, heart rate, and swimming performance of Odontophrynus americanus tadpoles

Odontoprynus americanus tadpoles were used to determine the safety concentration of pyriproxyfen (PPF) insecticide by acute and sublethal toxicity tests (nominal range tested 0.01 to 10 [± 15%] PPF mg/L). Median lethal concentration (LC₅₀) and no, and lowest-observed-effect concentrations (NOEC and LOEC, respectively) were calculated. We also assessed the effect on the activities of glutathione S-transferse (GST), acetylcholinesterase (AChE), and carboxylesterase (CbE) and compared to control (CO) tadpoles. Based on the 48-h NOEC value, two sublethal concentrations of PPF (0.01 and 0.1 mg/L) were assayed to detect effects on enzymes activities (GST and CbE), thyroid hormone's levels (triiodothyronine; T3 and thyroxine; T4), heart function, and tadpoles swimming behaviour. The results showed that the LC₅₀ values of O. americanus tadpoles were 3.73 PPF mg/L and 2.51 PPF mg/L at 24-h and 48-h, respectively (NOEC = 0.1 mg/L; LOEC = 1 mg/L, for both times). PPF concentrations at 48 h, induced enzymatic activities such as GST (212.98%-242.94%), AChE (142.15%-165.08%), and CbE (141.86%-87.14%) significantly respect to COs. During the 22 days of chronic PPF exposure, GST (0.01 mg/L 88%-153% NOEC), AChE (177.82% NOEC), and T4 (70% NOEC) also significantly increased respect to COs. Similarly, heart rate (fH) and ventricular cycle length (VV interval) in CO tadpoles were significantly higher than PPF treated. Finally, at NOEC tadpoles exhibited significant effects on the behavioral endpoint (swimming distance, mean speed, and global activity; P < 0.05).

Behavioral consequences of dietary exposure to crude oil extracts in the Siamese fighting fish (Betta splendens)

Uptake by fishes of crude oil and its polycyclic aromatic hydrocarbons (PAHs) components occurs via gills, dietary intake, or diffusion through the skin. Dietary exposure to crude oil and its components is environmentally relevant, and induces physiological and morphological disruptions in fish. However, the impacts of crude oil on fish social and reproductive behaviors and thus the possible influences on reproductive success are poorly understood. As a part of their intraspecific interactions, male Siamese fighting fish (Betta splendens) exhibit highly stereotypic behavioral and territorial displays. This makes this species a tractable model for testing crude oil effects on behavior. After 2 weeks of acclimation at 29 °C, male adult betta fish were divided into three groups and fed for 4 weeks with food spiked with water (control), low oil concentrations or high oil concentrations (∑Total PAH concentrations 340, 3960 or 8820 ng/g dw, respectively) to determine subsequent alterations in behavioral displays. Compared with control fish, the aggressive display of "opercular flaring" was significantly increased (P < 0.03, n = 14-16) in oil-exposed fish. Bubble nest building, as well as testis and brain mass, were significantly reduced in treated fish (P < 0.05). Hematocrit of treated groups was increased significantly (P < 0.02) from 21% in control fish to ∼27% in both oil exposure groups. Dietary exposure over a 4-week period to low, relevant levels of crude oil thus leads to an increase in aggressive behavioral displays, a decrease in reproductive activity and additional morphological changes.

Combined effects of elevated temperature and Deepwater Horizon oil exposure on the cardiac performance of larval mahi-mahi, Coryphaena hippurus

The 2010 Deepwater Horizon oil spill coincided with the spawning season of many pelagic fish species in the Gulf of Mexico. Yet, few studies have investigated physiological responses of larval fish to interactions between anthropogenic crude oil exposure and natural factors (e.g. temperature, oxygen levels). Consequently, mahi mahi (Coryphaena hippurus) embryos were exposed for 24 hours to combinations of two temperatures (26 and 30°C) and six concentrations of oiled fractions of weathered oil (from 0 to 44.1 μg ∑50PAHs·L^-1). In 56 hours post-fertilization larvae, heart rate, stroke volume and cardiac output were measured as indicators of functional cardiac phenotypes. Fluid accumulation and incidence of edema and hematomas were quantified as indicators of morphological impairments. At both 26 and 30°C, oil-exposed larvae suffered dose-dependent morphological impairments and functional heart failure. Elevation of temperature to 30°C appeared to induce greater physiological responses (bradycardia) at PAH concentrations in the range of 3.0–14.9 μg·L^-1. Conversely, elevated temperature in oil-exposed larvae reduced edema severity and hematoma incidence. However, the apparent protective role of warmer temperature does not appear to protect against enhanced mortality. Collectively, our findings show that elevated temperature may slightly decrease larval resilience to concurrent oil exposure.

Moderate hypoxia but not warming conditions at larval stage induces adverse carry-over effects on hypoxia tolerance of European sea bass (Dicentrarchus labrax) juveniles

Environmental conditions, to which organisms are exposed during all their life, may cause possible adaptive responses with consequences in their subsequent life-history trajectory. The objective of this study was to investigate whether ecologically relevant combinations of hypoxia (40% and 100% air saturation) and temperature (15° and 20 °C), occurring during the larval period of European sea bass larvae (Dicentrarchus labrax), could have long-lasting impacts on the physiology of resulting juveniles. Hypoxic challenge tests were performed over one year to give an integrative evaluation of physiological performance. We revealed that juvenile performance was negatively impacted by hypoxia but not by the thermal conditions experienced at larval stage. This impact was related to the prevalence of opercular abnormalities. The present study indicates that exposure to a moderate hypoxia event during larval stage may have adverse carry-over effects, which could compromise fitness and population recruitment success.

Characterization of igf1 and igf2 genes during maraena whitefish (Coregonus maraena) ontogeny and the effect of temperature on embryogenesis and igf expression

The insulin-like growth factors IGF-1 and IGF-2 play important roles in the growth, development, and metabolism of teleost fish. We isolated cDNA sequences of igf1, and igf2 genes from maraena whitefish. We quantified the mRNA and protein expressions of IGFs in different tissues of marketable juvenile maraena whitefish. Moreover, we analyzed the gene expression profiles during maraena whitefish development from unfertilized egg to fingerling and examined the effect of incubation temperature on igf1, and igf2 gene expression during embryonic and early larval development. Transcripts encoding IGF-1 or IGF-2 were detected in all tested tissues, with the greatest abundance in the liver. We measured higher igf2 than igf1 copy numbers in all tissues and at all developmental stages examined, even at advanced juvenile stages. Using the Western blot technique, we demonstrated that several isoforms of IGF-1 are expressed in the liver and gills but not in muscle tissue, indicating tissue-specific protein expression of IGF-1. We observed an accelerated embryonic development with increasing temperature, resulting in shortened hatching periods. Out of the three tested temperatures, we observed the highest hatching rate, larval hatching size, and larval growth at 6 °C. At 9 °C, hatching rate, larval hatching size and larval growth were reduced compared to the values we observed at 4 °C and 6 °C, since incubation temperature might have exceeded the optimum. To our knowledge, our data show for the first time that both igf1 and igf2 expression were upregulated due to elevated incubation temperature within embryonic development of fish. Further, we found significantly higher igf expression for the best-developing larvae (6 °C group) at specific life stages of maraena whitefish.

Developmental temperature has persistent, sexually dimorphic effects on zebrafish cardiac anatomy

Over the next century, climate change of anthropogenic origin is a major threat to global biodiversity. We show here that developmental temperature can have significant effects on zebrafish cardiac anatomy and swimming performance. Zebrafish embryos were subjected to three developmental temperature treatments (TD = 24, 28 or 32 °C) up to metamorphosis and then all maintained under common conditions (28 °C) to adulthood. We found that developmental temperature affected cardiac anatomy of juveniles and adults even eight months after the different thermal treatments had been applied. The elevation of TD induced a significant increase of the ventricle roundness in juvenile (10% increase) and male (22% increase), but not in female zebrafish. The aerobic exercise performance of adult zebrafish was significantly decreased as TD elevated from 24 to 32 °C. Gene expression analysis that was performed at the end of the temperature treatments revealed significant up-regulation of nppa, myh7 and mybpc3 genes at the colder temperature. Our work provides the first evidence for a direct link between developmental temperature and cardiac form at later life-stages. Our results also add to the emerging rationale for understanding the potential effects of global warming on how fish will perform in their natural environment.

Developmental phenotypic plasticity helps bridge stochastic weather events associated with climate change

The slow, inexorable rise in annual average global temperatures and acidification of the oceans are often advanced as consequences of global change. However, many environmental changes, especially those involving weather (as opposed to climate), are often stochastic, variable and extreme, particularly in temperate terrestrial or freshwater habitats. Moreover, few studies of animal and plant phenotypic plasticity employ realistic (i.e. short-term, stochastic) environmental change in their protocols. Here, I posit that the frequently abrupt environmental changes (days, weeks, months) accompanying much longer-term general climate change (e.g. global warming over decades or centuries) require consideration of the true nature of environmental change (as opposed to statistical means) coupled with an expansion of focus to consider developmental phenotypic plasticity. Such plasticity can be in multiple forms - obligatory/facultative, beneficial/deleterious - depending upon the degree and rate of environmental variability at specific points in organismal development. Essentially, adult phenotypic plasticity, as important as it is, will be irrelevant if developing offspring lack sufficient plasticity to create modified phenotypes necessary for survival.

Heart Performance Determination by Visualization in Larval Fishes: Influence of Alternative Models for Heart Shape and Volume

Understanding cardiac function in developing larval fishes is crucial for assessing their physiological condition and overall health. Cardiac output measurements in transparent fish larvae and other vertebrates have long been made by analyzing videos of the beating heart, and modeling this structure using a conventional simple prolate spheroid shape model. However, the larval fish heart changes shape during early development and subsequent maturation, but no consideration has been made of the effect of different heart geometries on cardiac output estimation. The present study assessed the validity of three different heart models (the "standard" prolate spheroid model as well as a cylinder and cone tip + cylinder model) applied to digital images of complete cardiac cycles in larval mahi-mahi and red drum. The inherent error of each model was determined to allow for more precise calculation of stroke volume and cardiac output. The conventional prolate spheroid and cone tip + cylinder models yielded significantly different stroke volume values at 56 hpf in red drum and from 56 to 104 hpf in mahi. End-diastolic and stroke volumes modeled by just a simple cylinder shape were 30-50% higher compared to the conventional prolate spheroid. However, when these values of stroke volume multiplied by heart rate to calculate cardiac output, no significant differences between models emerged because of considerable variability in heart rate. Essentially, the conventional prolate spheroid shape model provides the simplest measurement with lowest variability of stroke volume and cardiac output. However, assessment of heart function-especially if stroke volume is the focus of the study-should consider larval heart shape, with different models being applied on a species-by-species and developmental stage-by-stage basis for best estimation of cardiac output.