The effects of salinity and photoperiod on aerobic scope, hypoxia tolerance and swimming performance of coho salmon (Oncorhynchus kisutch) reared in recirculating aquaculture systems

One Health: Circadian Medicine Benefits Both Non-human Animals and Humans Alike

Circadian biology's impact on human physical health and its role in disease development and progression is widely recognized. The forefront of circadian rhythm research now focuses on translational applications to clinical medicine, aiming to enhance disease diagnosis, prognosis, and treatment responses. However, the field of circadian medicine has predominantly concentrated on human healthcare, neglecting its potential for transformative applications in veterinary medicine, thereby overlooking opportunities to improve non-human animal health and welfare. This review consists of three main sections. The first section focuses on the translational potential of circadian medicine into current industry practices of agricultural animals, with a particular emphasis on horses, broiler chickens, and laying hens. The second section delves into the potential applications of circadian medicine in small animal veterinary care, primarily focusing on our companion animals, namely dogs and cats. The final section explores emerging frontiers in circadian medicine, encompassing aquaculture, veterinary hospital care, and non-human animal welfare and concludes with the integration of One Health principles. In summary, circadian medicine represents a highly promising field of medicine that holds the potential to significantly enhance the clinical care and overall health of all animals, extending its impact beyond human healthcare.

The crosstalk between photoperiod and early mild stress on juvenile oscar (Astronotus ocellatus) after acute stress

Early mild stress (EMS) is like preparedness and might help fish deal with stress appropriately. This study investigated how EMS and photoperiod changes can impact growth, haematology, blood biochemistry, immunological response, antioxidant system, liver enzymes, and stress response of oscar (Astronotus ocellatus; 7.29 ± 0.96 g) before and after acute confinement stress (AC stress). Ten experimental treatments included five different photoperiods 8L16D (08:16 light to dark), 12L12D (12:12 light to dark), 16L8D (16:08 light to dark), 20L4D (20:04 light to dark), and 24L0D (24:00 light to dark), and these five photoperiod schedules were conducted in an EMS condition. After 9 weeks, no significant differences were found in growth parameters, survival rate, and body composition. At the end of the experiment and after AC stress, fish farmed in 24 light hours had the lowest haematocrit, white blood cells, total protein, blood performance, lysozyme, immunoglobulin M, complement C3, superoxide dismutase, and catalase. Fish that experienced EMS had significantly higher survival rates than those farmed in normal conditions (80.67% vs 61.33%). In conclusion, considering all measured parameters, 8-h light can be suggested as an optimum photoperiod for this fish species. Under 24L0D (no EMS) conditions, there were many negative effects apparent. In addition, a positive effect of EMS was evident in terms of survival after AC stress. AC stress decreased some health parameters under 24-h light treatment, while these results were not observed in EMS-exposed fish. Therefore, the EMS schedule can be a useful tool in preventing the negative effects of stress.

Increased reliance on coronary perfusion for cardiorespiratory performance in seawater-acclimated rainbow trout

Salmonid ventricles are composed of spongy and compact myocardium, the latter being perfused via a coronary circulation. Rainbow trout (Oncorhynchus mykiss) acclimated to sea water have higher proportions of compact myocardium and display stroke volume-mediated elevations in resting cardiac output relative to freshwater-acclimated trout, probably to meet the higher metabolic needs of osmoregulatory functions. Here, we tested the hypothesis that cardiorespiratory performance of rainbow trout in sea water is more dependent on coronary perfusion by assessing the effects of coronary ligation on cardiorespiratory function in resting and exhaustively exercised trout acclimated to fresh water or sea water. While ligation only had minor effects on resting cardiorespiratory function across salinities, cardiac function after chasing to exhaustion was impaired, presumably as a consequence of atrioventricular block. Ligation reduced maximum O2 consumption rate by 33% and 17% in fish acclimated to sea water and fresh water, respectively, which caused corresponding 41% and 17% reductions in aerobic scope. This was partly explained by different effects on cardiac performance, as maximum stroke volume was only significantly impaired by ligation in sea water, resulting in 38% lower maximum cardiac output in seawater compared with 28% in fresh water. The more pronounced effect on respiratory performance in sea water was presumably also explained by lower blood O2 carrying capacity, with ligated seawater-acclimated trout having 16% and 17% lower haemoglobin concentration and haematocrit, respectively, relative to ligated freshwater trout. In conclusion, we show that the coronary circulation allows seawater-acclimated trout to maintain aerobic scope at a level comparable to that in fresh water.

Nuclear and Morphological Alterations in Erythrocytes, Antioxidant Enzymes, and Genetic Disparities Induced by Brackish Water in Mrigal Carp (Cirrhinus mrigala)

Salinization of aquatic ecosystem, abrupt climate change, and anthropogenic activities cause adverse impact on agricultural land/soil as well as the aquaculture industry. This experimental study was designed to evaluate different biomarkers of oxidative stress, antioxidant enzymes, and genotoxic potential of diverse salinities of brackish water on freshwater fish. A total of 84 fresh water mrigal carp (Cirrhinus mrigala) were randomly segregated and maintained in four groups (T0, T1, T2, and T3) in a glass aquarium under similar laboratory conditions at various salinity levels (0, 3, 5, and 7 parts per thousand) to determine the pathological influence of brackish water. All the fish in groups T1, T2, and T3 were exposed to various salinity levels of brackish water for a period of 90 days while the fish of group T0 served as the control group. The experimental fish reared in different groups T1, T2, and T3 displayed various physical and behavioral ailments. The results revealed significantly augmented quantity of different oxidative stress indicators including reactive oxygen species (ROS) and thiobarbituric acid reactive substance (TBARS) in different visceral tissues (kidneys, liver, and gills) of exposed fish. Different antioxidant enzymes such as reduced glutathione (GSH), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) along with total proteins were remarkably reduced in the kidneys, gills, and liver tissues. Results showed significantly increased values of different nuclear abnormalities (erythrocyte with micronucleus, erythrocyte with condensed nucleus, and erythrocyte with lobed nucleus) and morphological changes (pear shaped erythrocyte, spindle-shaped erythrocytes, and spherocyte) in red blood cells of experimental fish. The results on genotoxic effects exhibited significantly increased DNA damage in isolated cells of liver, kidneys, and gills of exposed fish. The findings of our experimental research suggested that brackish water causes adverse toxicological impacts on different visceral tissues of fresh water fish at higher salinity level through disruption and disorder of physiological and biochemical markers.

Diluted bitumen-induced alterations in aerobic capacity, swimming performance, and post-exercise recovery in juvenile sockeye salmon (Oncorhynchus nerka)

The transportation of heavy crudes such as diluted bitumen (dilbit) sourced from Canadian oil sands through freshwater habitat requires the generation of information that will contribute to risk assessments, spill modelling, management, and remediation for the protection of aquatic organisms. Juvenile sockeye salmon (Oncorhynchus nerka) were exposed acutely (96 h) or subchronically (28 d) to the water-soluble fraction (WSFd) of Cold Lake Blend dilbit at initial total polycyclic aromatic compound (TPAC) concentrations of 0, 13.7, 34.7, and 124.5 µg/L. A significant induction (>3-fold) of hepatic liver ethoxyresorufin-O-deethylase (EROD) activity was induced by 96 h in fish exposed to [TPAC] ≥ 34.7 µg/L and at ≥13.7 µg/L for a 28 d exposure. Exposure resulted in a typical physiological stress response and disturbance of ion homeostasis; this included elevations in plasma [cortisol], [lactate], [Na⁺], and [Cl^-], and significant reductions in muscle [glycogen]. Critical swimming speed (U_crit) was significantly reduced (28.4%) in the acute exposure at [TPAC] 124.5 µg/L; reductions of 14.2% and 35.4% were seen in fish subchronically exposed at the two highest concentrations. Reductions in U_crit were related to significant reductions in aerobic scope (24.3-46.6%) at [TPAC]s of 34.7 and 124.5 µg/L, respectively. Exposure did not impair the ability to mount a secondary stress response following burst exercise, however, the time required for biochemical parameters to return to baseline values was prolonged. Alterations in critical systems supporting swimming, exercise recovery and the physiological stress response could result in decreased salmonid fitness and contribute to population declines if a dilbit spill occurs.

Swimming behavior of emigrating Chinook Salmon smolts

Swimming behavior of Chinook Salmon (Oncorhynchus tshawytscha) smolts affects transit time, route selection and survival in complex aquatic ecosystems. Behavior quantified at the river reach and junction scale is of particular importance for route selection and predator avoidance, though few studies have developed field-based approaches for quantifying swimming behavior of juvenile migratory fishes at this fine spatial scale. Two-dimensional acoustic fish telemetry at a river junction was combined with a three-dimensional hydrodynamic model to estimate in situ emigration swimming behavior of federally-threatened juvenile Chinook salmon smolts. Fish velocity over ground was estimated from telemetry, while the hydrodynamic model supplied simultaneous, colocated water velocities, with swimming velocity defined by the vector difference of the two velocities. Resulting swimming speeds were centered around 2 body lengths/second, and included distinct behaviors of positive rheotaxis, negative rheotaxis, lateral swimming, and passive transport. Lateral movement increased during the day, and positive rheotaxis increased in response to local hydrodynamic velocities. Swim velocity estimates were sensitive to the combination of vertical shear in water velocities and vertical distribution of fish.

Growth, feed conversion, sexual maturation, and cataract formation in coho (Oncorhynchus kisutch) and Atlantic (Salmo salar) salmon post-smolts reared at different salinities in recirculating aquaculture systems for over one year

There is increasing interest in defining optimal conditions for rearing salmon to market size in recirculating aquaculture systems (RAS). Salinity, however, as a parameter that can be potentially manipulated, has been poorly studied. To address this knowledge gap, we reared coho (Oncorhynchus kisutch (Walbaum, 1792)) and Atlantic (Salmo salar Linnaeus, 1758) salmon from smolt to market size over ∼460 days at five different salinities (0, 5, 10, 20, and 30 ppt) and examined their growth performance. We found that both species reared at intermediate salinities (5–10 ppt) started to show significantly larger body mass than fish reared either in freshwater or full-strength seawater at around days 250–300. These growth-enhancing effects were maintained until day 460. The higher growth in Atlantic salmon at intermediate salinities was associated with a reduced economic feed conversion ratio, but this was not observed in coho salmon. The all-female coho salmon showed no incidence of sexual maturation and negligible cataract formation, while the mixed-sex Atlantic salmon showed high levels of sexual maturation (up to 50%) and presence of cataracts (up to 60%). Our results indicate that all-female coho salmon may be better suited to RAS than Atlantic salmon in some aspects. However, in both species, long-term rearing at intermediate salinities improved growth in RAS.

Continuous light (relative to a 12:12 photoperiod) has no effect on anxiety-like behaviour, boldness, and locomotion in coho salmon (Oncorhynchus kisutch) post-smolts in recirculating aquaculture systems at a salinity of either 2.5 or 10 ppt

There is increased interest in rearing salmon in Recirculating Aquaculture Systems (RAS), where environmental conditions can be tightly controlled to optimize growth. Photoperiod and salinity are two important parameters that can be manipulated in RAS. A longer photoperiod permits more time for feeding, while intermediate salinities may reduce the energetic costs of ionoregulation, both of which may enhance growth. However, little is known about how rearing at different photoperiods and salinity affect behaviour, an understudied but important research topic for intensive fish rearing. To address this, we examined the behavioural effects of two salinities and two photoperiod regimes in coho salmon (Oncorhynchus kisutch) post-smolts reared continuously for 120 days in a RAS. Fish were reared on a photoperiod of either 12 h light:12 h dark (12:12), or 24 h light (24:0) at salinities of 2.5 and 10 ppt. To investigate behavioural differences associated with these treatments, we quantified: i) movement in an open-field test, ii) exploratory behaviour/boldness using a novel object approach test, and iii) anxiety-like behaviour with a light/dark test. The 24:0 groups displayed no differences in boldness/anxiety-like behaviour and locomotion relative to the 12:12 groups at their respective salinities. Taken together, fish reared under continuous light (24:0) show negligible behavioural alterations compared to fish reared under normal light dark conditions (12:12).

Dusky Grouper Epinephelus marginatus Growth and Survival When Exposed to Different Photoperiods

Photoperiod is considered an environmental factor that influences reproduction and the growth processes of fish throughout the year. In the present study, we subjected dusky grouper Epinephelus marginatus to different photoperiods in order to evaluate growth and survival. Juvenile dusky grouper were randomly distributed in twelve 100 L tanks containing four fish per aquarium. The fish were exposed to continuous light, normal photoperiod or continuous darkness for 50 days. Fish were fed 3% of their total biomass, twice a day, and the diet consisted of ground commercial dry pellets (42% crude protein, 12% humidity, 9% ether extract, 15% mineral matter, 4% crude fiber, 3.5% calcium and 3% vitamin C, in accordance with the manufacturer’s instructions). There was no mortality during the experiment. After 50 days, the best performance was found for exposure to continuous light (24 h artificial light). The final weight of the fish reared under continuous light was significantly higher than that of the fish exposed to continuous darkness. The specific growth rate of the fish exposed to continuous light was significantly higher than that of the fish exposed to the natural photoperiod and to continuous darkness. Modifications to the photoperiod can be a key factor in increasing the efficacy of current production and the improvement of current aquaculture protocols.

Environmental modulators of diluted bitumen effects in juvenile pink salmon (Oncorhynchus gorbuscha)

Recent and potential expansions in the transportation of diluted bitumen (dilbit) through marine terminals in coastal regions of British Columbia require the examination of potential risks to estuarine species such as Pacific salmon. The estuarine habitat of out-migrated pink salmon (Oncorhynchus gorbuscha) exhibits dynamic temperature and salinity regimes, possibly modifying dilbit exposure, bioavailability and/or its effects. To examine dilbit toxicity and its modification by environmental stressors, juvenile pinks were subchronically exposed for 3 months to the water-accommodated fraction (WAF) of Cold Lake Blend dilbit (winter) in seawater at three salinities (7, 14, and 28‰ [temperature 12.5 °C]) and three temperatures (8.5, 12.5, and 16.5 °C [salinity of 28‰]). Temperature and salinity alone did not affect any measured endpoints in control fish. Dilbit exposure induced higher mortality at high (16.5 °C) and low temperatures (8.5 °C) as well as at higher salinity (28‰) in fish exposed to the highest dilution of WAF [total polycyclic aromatic compounds (TPAC) = 128.9 μg/L]. A concentration-dependent reduction of growth was evident in fish exposed to the medium (TPAC = 97.3 μg/L) and high dilution of WAF at higher temperatures (12.5 and 16.5 °C) and high salinity (28‰). At 28‰, swimming performance (U_burst) was decreased in fish exposed to the highest concentration of dilbit at all 3 temperatures. Gill Na⁺-K⁺-ATPase activity, white muscle lactate, glycogen, and triglyceride concentrations were altered by dilbit exposure and modified by temperature and salinity. In addition, gene expression associated with phase I biotransformation, energy metabolism, mitochondrial activity, and inflammation showed significant upregulation with exposure and temperature stress. Dilbit exposure at PAC concentrations in the ppb range, affected pink salmon at the molecular, biochemical, and whole organism level; effects that were exacerbated by environmental temperature and salinity.

Modulation of physiological oxidative stress and antioxidant status by abiotic factors especially salinity in aquatic organisms

Exposure to a variety of environmental factors such as temperature, pH, oxygen and salinity may influence the oxidative status in aquatic organisms. The present review article focuses on the modulation of oxidative stress with reference to the generation of reactive oxygen species (ROS) in aquatic animals from different phyla. The focus of the review article is to explore the plausible mechanisms of physiological changes occurring in aquatic animals due to altered salinity in terms of oxidative stress. Apart from the seasonal variations in salinity, global warming and anthropogenic activities have also been found to influence oxidative health status of aquatic organisms. These effects are discussed with an objective to develop precautionary measures to protect the diversity of aquatic species with sustainable conservation. Comparative analyses among different aquatic species suggest that salinity alone or in combination with other abiotic factors are intricately associated with modulation in oxidative stress in a species-specific manner in aquatic animals. Osmoregulation under salinity stress in relation to energy demand and supply are also discussed. The literature survey of >50 years (1960-2020) indicates that oxidative stress status and comparative analysis of redox modulation have evolved from the analysis of various biotic and/or abiotic factors to the study of cellular signalling pathways in these aquatic organisms.

Inter-population differences in salinity tolerance of adult wild Sacramento splittail: osmoregulatory and metabolic responses to salinity

The Sacramento splittail (Pogonichthys macrolepidotus) is composed of two genetically distinct populations endemic to the San Francisco Estuary (SFE). The allopatric upstream spawning habitat of the Central Valley (CV) population connects with the sympatric rearing grounds via relatively low salinity waters, whereas the San Pablo (SP) population must pass through the relatively high-salinity Upper SFE to reach its allopatric downstream spawning habitat. We hypothesize that if migration through SFE salinities to SP spawning grounds is more challenging for adult CV than SP splittail, then salinity tolerance, osmoregulatory capacity, and metabolic responses to salinity will differ between populations. Osmoregulatory disturbances, assessed by measuring plasma osmolality and ions, muscle moisture and Na⁺-K⁺-ATPase activity after 168 to 336 h at 11‰ salinity, showed evidence for a more robust osmoregulatory capacity in adult SP relative to CV splittail. While both resting and maximum metabolic rates were elevated in SP splittail in response to increased salinity, CV splittail metabolic rates were unaffected by salinity. Further, the calculated difference between resting and maximum metabolic values, aerobic scope, did not differ significantly between populations. Therefore, improved osmoregulation came at a metabolic cost for SP splittail but was not associated with negative impacts on scope for aerobic metabolism. These results suggest that SP splittail may be physiologically adjusted to allow for migration through higher-salinity waters. The trends in interpopulation variation in osmoregulatory and metabolic responses to salinity exposures support our hypothesis of greater salinity-related challenges to adult CV than SP splittail migration and are consistent with our previous findings for juvenile splittail populations, further supporting our recommendation of population-specific management.