Hyperthermia induced atrial natriuretic peptide expression and deviant heart development in Atlantic salmon Salmo salar embryos

Temperature regime during embryogenesis alters subsequent behavioural phenotypes of juvenile brown trout

Climate warming imposes a serious threat, especially to freshwater ecosystems in temperate and (sub)polar regions, which are often dominated by cold-adapted ectotherms. Although relatively intense warming during winter is common across the climatic regions, comparably little focus has been put on the organismal impacts of winter warming. Embryonic development, which is exceptionally susceptible to ambient temperature, occurs during winter in various freshwater ectotherms. Yet, our knowledge of the effects of increased temperature during embryogenesis on later life stages is limited. Using brown trout ( Salmo trutta ), we examined how a 1.5°C temperature increase from fertilization to hatching affects various traits at the onset of the free-swimming stage (i.e. a comparison between 3.5 and 5.0°C treatments). Although all hatchlings were kept at the same temperature (7.0°C) from hatching to the onset of the free-swimming stage for about two months, the temperature increase during embryogenesis substantially reduced key ecological behaviours, i.e. activity and exploration levels, at the onset of the free-swimming stage despite only marginal temperature effects on morphological and physiological traits at this stage. Given the importance of behavioural traits in early growth and survival, our study suggests a likely pathway through which subtle changes in mean winter temperature affect early fitness.

Development of an Atlantic salmon heart endothelial cell line (ASHe) that responds to lysophosphatidic acid (LPA)

As diseases and abnormalities of the heart can interfere with the aquaculture of Atlantic salmon, the heart was investigated as a source of cell lines that could be used to study the cellular basis of these conditions. An Atlantic salmon heart endothelial cell line, ASHe, was developed and characterized for growth properties, endothelial cell characteristics, and responsiveness to lysophosphatidic acid (LPA). AHSe cells stained negative for senescence associated ß-galactosidase and grew well in 10 and 20% FBS/L15 at high cell density, but not in L15 medium supplemented with calf serum. It displayed many endothelial cell-like characteristics including a cobblestone morphology, capillary-like structures formation on Matrigel, and expression of von Willebrand factor and endothelial cell-related tight junction proteins ZO-1, claudin 3, and claudin 5. ASHe cells responded to the cardiovascular modulator, LPA, in two contrasting ways. LPA at 5 and 25 μM inhibited the ability of ASHe cells to heal a wound but stimulated their proliferation, especially as evaluated by colony formation in low-density cultures. The enhancement of proliferation by LPA parallels what has been observed previously in mammalian endothelial cell cultures exposed to LPA, whereas the LPA slowing of ASHe cell migration contrasted with the LPA-enhanced migration of some mammalian cells. Therefore, this cell line is a potentially useful model for future comparative studies on piscine and mammalian cardiovascular cell biology and for studies on diseases of Atlantic salmon in aquaculture.

Point-of-care devices for physiological measurements in field conditions. A smorgasbord of instruments and validation procedures

Point-of-care (POC) devices provide quick diagnostic results that increase the efficiency of patient care. Many POC devices are currently available to measure metabolites, blood gases, hormones, disease biomarkers or pathogens in samples as diverse as blood, urine, feces or exhaled breath. This diversity is potentially very useful for the comparative physiologist in field studies if proper validation studies are carried out to justify the accuracy of the devices in non-human species under different conditions. Our review presents an account of physiological parameters that can be monitored with POC devices and surveys the literature for suitable quantitative and statistical procedures for comparing POC measurements with reference "gold standard" procedures. We provide a set of quantitative tools and report on different correlation coefficients (Lin's Concordance Correlation Coefficient or the more widespread Pearson correlation coefficient), describe the graphical assessment of variation using Bland-Altman plots and discuss the difference between Model I and Model II regression procedures. We also report on three validation datasets for lactate, glucose and hemoglobin measurements in birds using the newly proposed procedures. We conclude the review with a haphazard account of future developments in the field, emphasizing the interest in lab-on-a-chip devices to carry out more complex experimental measurements than the ones currently available in POC devices.

The effect of ploidy and incubation temperature on survival and the prevalence of aplasia of the septum transversum in Atlantic salmon, Salmo salar L

Heart deformities are a concern in aquaculture and are linked to egg incubation temperature. Diploid and triploid Atlantic salmon, Salmo salar L., were incubated at 6, 8 and 10 °C and analysed for aplasia of the septum transversum (n = 150 ploidy⁻¹ incubation temperature⁻¹). Heart morphology (size and shape) was assessed in fish incubated at 6 °C and in fish with and without aplasia of the septum transversum (n = 9 group⁻¹) incubated at 10 °C. Egg mortality was significantly higher in triploids than in diploids at all incubation temperatures, and increased egg incubation temperatures increased mortality in both ploidy. Triploids grew quicker than diploids after egg incubation at 10 °C, but not at 6 °C. Aplasia of the septum transversum occurred only in triploid fish after incubation at 6 °C and 8 °C (0.7% and 3.3%, respectively) and was significantly greater (P ≤ 0.05) in triploids after incubation at 10 °C compared with diploids (30% and 18%, respectively). Aplasia of the septum transversum significantly increased heart mass and resulted in a long flat ventricle compared with fish displaying a septum transversum. The results suggest triploid salmon should be incubated below 8 °C.

Cortisol response to stress is associated with myocardial remodeling in salmonid fishes

Cardiac disease is frequently reported in farmed animals, and stress has been implicated as a factor for myocardial dysfunction in commercial fish rearing. Cortisol is a major stress hormone in teleosts, and this hormone has adverse effects on the myocardium. Strains of rainbow trout (Oncorhynchus mykiss) selected for divergent post-stress cortisol levels [high responsive (HR) and low responsive (LR)] have been established as a comparative model to examine how fish with contrasting stress-coping styles differ in their physiological and behavioral profiles. We show that the mean cardiosomatic index (CSI) of adult HR fish was 34% higher than in LR fish, mainly because of hypertrophy of the compact myocardium. To characterize the hypertrophy as physiological or pathological, we investigated specific cardiac markers at the transcriptional level. HR hearts had higher mRNA levels of cortisol receptors (MR, GR1 and GR2), increased RCAN1 levels [suggesting enhanced pro-hypertrophic nuclear factor of activated T-cell (NFAT) signaling] and increased VEGF gene expression (reflecting increased angiogenesis). Elevated collagen (Col1a2) expression and deposition in HR hearts supported enhanced fibrosis, whereas the heart failure markers ANP and BNP were not upregulated in HR hearts. To confirm our results outside the selection model, we investigated the effect of acute confinement stress in wild-type European brown trout, Salmo trutta. A positive correlation between post-stress cortisol levels and CSI was observed, supporting an association between enhanced cortisol response and myocardial remodeling. In conclusion, post-stress cortisol production correlates with myocardial remodeling, and coincides with several indicators of heart pathology, well-known from mammalian cardiology.

Differential spatial expression of mef2 paralogs during cardiac development in Atlantic cod (Gadus morhua)

The myogenic enhancer factor 2 (Mef2) transcription factors are known for their role in the control of cardiac development. Here we describe the spatial and temporal expression patterns of five Atlantic cod mef2 genes designated as mef2a, mef2cI, mef2cII, mef2dI and mef2dII during cardiogenesis. Whole mount in situ hybridization showed that mef2a and mef2dI were expressed in both cardiac ring and cone prior to looping morphogenesis, while mef2dII expression was only detectable in the cardiac ring. The mef2cI and mef2cII paralogs displayed different spatial expression patterns in the heart tube with a venous and arterial pole preference, respectively. After the cardiac loop formation mef2cI was expressed in cells of the ventricle and lateral arteries, while mef2cII appeared more abundant and was also present in the atrium. Larvae raised at constant 8 °C showed malformed morphology of the lateral arteries, and the transcription of both mef2c variants was highly elevated compared to those kept at 4 °C. Acute temperature stress also resulted in deviations in the expression of the mef2c paralogs, and the treated embryos displayed defects in the developing heart, including impaired fusion of the bilateral primordia and truncated heart tubes.

Suspected myocardial necrosis in farmed Atlantic salmon, Salmo salar L.: a field case

Arteriosclerosis of the coronary artery has been described as a 'fact of life' for Pacific and Atlantic salmonids due to the high prevalence in spawning fish. The lesions are believed to be the result of overstretching of the highly distensible bulbus arteriosus whereby the endothelium of the main coronary vessel becomes mechanically damaged and a smooth muscle proliferation ensues with resultant partial occlusion of the vessel. The physiological significance for the function of the heart has yet to be demonstrated, but experimental studies show that, for example, swimming performance is compromised in fish in which the coronary artery has been ligated. This paper describes a case of myocardial necrosis in harvest-size Atlantic salmon during and after transportation to the slaughterhouse. Mortality during this process reached 10% in some of the transports and affected fish showed characteristic signs of congestive cardiac failure. Histology revealed extensive myointimal proliferation in the coronary artery and patchy necrosis of the compact ventricular myocardium. Several unfavourable factors such as high water temperature, skeletal malformations and crowding all probably contributed to extra cardiac workload. To the best of our knowledge, this is the first reported field case showing a link between coronary lesions and severe cardiac pathology.

The physiology and toxicology of salmonid eggs and larvae in relation to water quality criteria

The purpose of this review is to collate physiological knowledge on salmonid eggs and larvae in relation to water quality criteria. Salmonid genera reviewed include Coregonus, Thymallus, Salvelinus, Salmo, and Oncorhynchus spp. When physiological data for salmonids are lacking, the zebrafish and medaka models are included. The primary focus is on the underlying mechanisms involved in the hydro-mineral, thermal, and respiratory biology with an extended section on the xenobiotic toxicology of the early stages. Past and present data reveal that the eggs of salmonids are among the largest shed by any broadcast spawning teleost. Once ovulated, the physicochemical properties of the ovarian fluid provide temporary protection from external perturbations and maintain the eggs in good physiological condition until spawning. Following fertilisation and during early development the major structures protecting the embryo from poor water quality are the vitelline membrane, the enveloping layer and the chorion. The vitelline membrane is one of the least permeable membranes known, while the semi-permeable chorion provides both physical and chemical defense against metals, pathogens, and xenobiotic chemicals. In part these structures explain the lower sensitivity of the eggs to chemical imbalance compared to the larvae, however the lower metabolic rate and the chronology of gene expression and translational control suggest that developmental competence also plays a decisive role. In addition, maternal effect genes provide a defense potential until the mid-blastula transition. The transition between maternal effect genes and zygotic genes is a critical period for the embryo. The perivitelline fluids are an important trap for cations, but are also the major barrier to diffusion of gases and solutes. Acidic environmental pH interferes with acid-base and hydromineral balance but also increases the risk of aluminium and heavy metal intoxication. These risks are ameliorated somewhat by the presence of ambient humic acid. High temperatures during development may be teratogenic, cause sexual bias, or long-term effects on muscle cellularity. Xenobiotics cause inhibition of neural acetylcholine esterase and carboxylases and disrupt the normal signalling pathways of hormones by binding to relevant receptors and mimicking their actions. A complex suite of genes is activated in response to environmental or parentally transmitted xenobiotics. The primary defense mechanism in embryos involves resistance to uptake but later biotransformation via the aryl hydrocarbon receptor (AHR)-mediated activation of members of the cytochrome mixed-function mono-oxygenase superfamily (CYP1A, CYP2B, and CYP3A) and subsequent glucuronidation or glutathionation. Due to the number of duplicate or triplicate genes coding for intermediates in the signalling pathways, and cross-talk between nuclear orphan receptors and steroid hormone receptors, a large number of complications arise in response to xenobiotic intoxicaton. One such syndrome, known as blue-sac disease causes an anaphylactoid response in hatched larvae due to increased permeability in the vascular endothelium that coincides with AHR-mediated CYP induction. Early embryos also respond to such xenobiotic insults, but apparently have an immature translational control for expression of CYP proteins, which coincides with a lack of excretory organs necessary for the end-point of biotransformation. Other syndromes (M74 and Cayuga) are now associated with thiamine deficiency. Where possible guidelines for water quality criteria are suggested.

Myocardial glycogen storage disease in farmed rainbow trout, Oncorhynchus mykiss (Walbaum)

This paper is the first description of a spontaneous glycogen-storage disease in a lower vertebrate, as previous descriptions deal with humans and other mammals, or fish where the condition has been experimentally induced. Affected farmed rainbow trout experienced increased mortality from 60 days post-startfeeding and displayed clinical signs of heart failure with abnormal behaviour, exophthalmia, distended abdomen and ventral skin petechiation. Necropsy revealed alterations in cardiac shape with distended atria and rounded ventricles. Microscopically, the compact wall of the ventricle was absent, uneven or thinner than normal. The cardiac myocytes contained extensive amounts of glycogen in cytoplasmic vacuoles as demonstrated by periodic acid-Schiff staining that was abolished by saliva-diastase pretreatment on serial sections. Associated lesions included conspicuous subepicardial and myocardial vascularization, epicardial thickening and necrosis of the ventricular compactum/spongiosum interphase. The lesions in cardiac myocytes had a striking resemblance to glycogenosis type II (Pompe disease), a rare autosomal recessive lysosomal storage disease in humans. This condition was more severe and mortality was higher in a replicate/parallel fish group treated perorally with 17alpha-methyltestosterone to produce all-female progeny, indicating that the hormone treatment aggravated the condition resulting in earlier and more severe manifestation of the disease in this group.