Behavioral Changes in a Coastal Marine Fish Lead to Increased Predation Risk Following Oil Exposure

Crude oil, hypoxia, or their combination affects adult brain morphology and offspring growth but not social and exploratory behaviors in zebrafish

Environmental stressors can impact fish populations by altering individuals' behavior and physiology. Exposure in fish to crude oil or hypoxia affects physiological processes and leads to behavioral impairments such as increased anxiety-like behavior and aggression. However, the effects of parental exposure to crude oil and hypoxia on the F1 offspring remain poorly explored. We investigated the growth and brain morphology of parental zebrafish exposed for five weeks to: 1) Control conditions (normoxic water, control diet); 2) Hypoxia (60 % air saturation hypoxic water, control diet); 3) HEWAF (normoxic water, HEWAF-loaded diet); and 4) Hypoxia-HEWAF (60 % air saturation hypoxic water, HEWAF-loaded diet). Adults were bred at 0- and 30-days post exposure (DPE) to determine if potential cross-generational effects "wash in" or "wash out" over time on the growth and behavior of the offspring. Tests of sociability (swimming speed, time to approach, and time spent near conspecifics) and exploration (swimming speed, time to approach novel object) were performed in clean, normoxic water on F1 larvae at 19-20 dpf. The size of the right optic tectum decreased in adult fish dietarily exposed to crude oil. Additionally, larvae from parents exposed to crude oil and hypoxia independently produced offspring that had lower mass and length at 0 DPE, but only the larvae from parents exposed to hypoxia remained smaller at 30 DPE. However, social and exploratory behaviors, as well as swimming speed, were not affected in offspring of any parental oil or hypoxia treatment group. Our results indicate that, despite inheritance of reduced body size, offspring behavior remained unaffected, suggesting that an important aspect of larval fitness is influenced by parental stressor exposure.

Bioaccumulation and behavioral response patterns of crucian carp (Carassius carassius) after carbamazepine exposure and elimination

The antiepileptic drug carbamazepine (CBZ) has been widely detected in freshwater, yet its toxic actions in fish at multiple endpoints and the subsequent recovery patterns of the impacted are less discussed. This study investigated the bioaccumulation, physiological and behavioral changes of crucian carp (Carassius carassius) following CBZ exposure (G1 = 6.15 μg/L, G2 = 61.5 μg/L, G3 = 615 μg/L, G4 = 6150 μg/L) and subsequent recovery. Our results showed that CBZ was more likely to accumulate in the liver and brain than in the gills. A concentration-dependent phenomenon was observed; however, the residual CBZ decreased to similar levels after recovery. The behavioral indicators (i.e. feeding, social and spontaneous swimming) were significantly inhibited after 7-days of CBZ exposure, and only recovered at low concentration treatment (G1) after 7-days recovery in CBZ-free water. The acetylcholinesterase (AChE) activity in the brain and superoxide dismutase (SOD) activity in the liver and gills were induced after CBZ exposure and returned to normal levels after 7-days of recovery. In contrast, the inhibition of catalase (CAT) activity caused by CBZ exposure persisted in the high concentration treatment (G4) after recovery. Furthermore, correlation analysis indicated that changes in feeding behavior were closely related to the variation of CBZ concentrations in tissues, and the persistence of abnormal swimming and social behavior was closely related to gill CAT activity. These findings contribute to explore the toxic mechanisms of CBZ and highlight the recovery process and connections between various endpoints.

Time-series variation in the locomotor behavior and vocal traits of Japanese medaka (Oryzias latipes) acutely exposed to organophosphorus pesticide chlorpyrifos

Organophosphorus pesticides (OPs), such as chlorpyrifos (CPF), are the most commonly used pesticides worldwide. Considering that OPs will eventually enter aquatic ecosystems due to runoff from agricultural lands, accidental leakage, and other unforeseen emergencies, monitoring water pollution of those substances is crucial for environmental protection and public health. In this study, Japanese medaka (Oryzias latipes) were exposed to CPF (0.03, 0.06, and 0.12 mg/L) for 6 h, and the time-series variations in their locomotor behavior and vocal traits were investigated. Compared with that measured before exposure, significantly changed locomotor behavior and vocal traits in Japanese medaka exposed to CPF could be observed at 4 h after exposure and thereafter, and the pattern of behavioral changes depends on the CPF concentrations. Exposure to CPF also changed the frequency-sound pressure level curve of Japanese medaka at 6 h after exposure, especially at 0.12 mg/L. Moreover, CPF exposure could significantly inhibit the acetylcholinesterase (AChE) activity in the brains and eyes of medaka, which exhibited significant correlations with the variation of locomotor behavioral and vocal traits. Considering that inhibiting the AChE activity is the primary mechanism underlying the neurobehavioral toxicity of all OPs, our finding suggested that simultaneously monitoring changes in the locomotor behavioral and vocal traits has a high potential to reflect the pollution of organophosphorus substances.

Behavioral profile alterations and predation susceptibility of Japanese medaka fish exposed to phenytoin, an antiepileptic drug

Antiepileptic drugs, such as phenytoin, are often leaked into aquatic systems through sewage facilities due to their low metabolic rate. Fish, such as the Japanese medaka (Oryzias latipes), demonstrate abnormal swimming behavior such as equilibrium abnormalities, rotational behavior, and vertical swimming, when exposed to phenytoin. Therefore, it is hypothesized that predator avoidance may be hindered. This study aimed to investigate the effects of phenytoin exposure-induced behavioral abnormalities in predator avoidance in Japanese medaka. The results showed that individuals with behavioral abnormalities had a reduced ability to avoid danger. Furthermore, the fish demonstrated a delayed recognition reaction to approaching predators. Additionally, predatory fish, such as silver pike characin (Ctenolucius hujeta), were more likely to prey upon abnormal individuals. In conclusion, the fish exposed to phenytoin demonstrated behavioral changes that increased its predation risk. This study is the first to determine the effects of behavioral abnormalities in Japanese medaka which was induced after phenytoin exposure on predator risk avoidance.

Diazepam at environmentally relevant concentrations disturbed social interactions and brain neurotransmitters in adult Japanese medaka (Oryzias latipes)

Pollution by diazepam (DZP) is increasingly recognized as a major threat to aquatic organisms, but knowledge about its potential risk to fish is still limited. In this study, we exposed female and male Japanese medaka (Oryzias latipes) to environmentally relevant DZP (0.8 and 8 µg/L) for 28 days and investigated variation in their behavior (on days 7, 14, and 28) and brain neurotransmitter levels (on day 28). The results showed that DZP could be accumulated in the brain and gonads in Japanese medaka. When two fish of the same sex were placed in an aquarium, DZP exposure exhibited typical sedative effects on females (on day 7) and males (on days 7 and 14). However, these sedative effects on both sexes were no longer present after 28 days of exposure. Exposure to DZP induced sex-specific impacts on the social interactions of medaka on days 7, 14, and 28 of exposure in a time-dependent manner. When both sexes were placed into an aquarium in a ratio of 1:1, DZP could significantly alter their locomotor activity and social interaction on days 14 and 28 of the exposure. After 28 days of exposure, DZP significantly altered the levels of several neurotransmitters in the brain of medaka, also in sex-specific manners. The alterations in dopamine and serotonin levels exhibited significant correlations with the increased social interaction between females. At the same time, that of γ-aminobutyric acid significantly correlated to the decreased social interaction between males. Our findings suggest that chronic exposure to DZP, even at environmentally relevant concentrations, can accumulate in the brains and gonads of fish, and alter their behaviors by mediating brain neurotransmitter levels, which may further disturb their reproduction and population dynamics.

The role of carbonic anhydrase-mediated tissue oxygen extraction in a marine teleost acclimated to hypoxia

With the growing prevalence of hypoxia (O2 levels ≤2 mg l−1) in aquatic and marine ecosystems, there is increasing interest in the adaptive mechanisms fish may employ to better their performance in stressful environments. Here, we investigated the contribution of a proposed strategy for enhancing tissue O2 extraction – plasma-accessible carbonic anhydrase (CA-IV) – under hypoxia in a species of estuarine fish (red drum, Sciaenops ocellatus) that thrives in fluctuating habitats. We predicted that hypoxia-acclimated fish would increase the prevalence of CA-IV in aerobically demanding tissues to confer more efficient tissue O2 extraction. Furthermore, we predicted the phenotypic changes to tissue O2 extraction that occur with hypoxia acclimation may improve respiratory and swim performance under 100% O2 conditions (i.e. normoxia) when compared with performance in fish that have not been acclimated to hypoxia. Interestingly, there were no significant differences in relative CA-IV mRNA expression, protein abundance or enzyme activity between the two treatments, suggesting CA-IV function is maintained under hypoxia. Likewise, respiratory performance of hypoxia-acclimated fish was similar to that of control fish when tested in normoxia. Critical swim speed (Ucrit) was significantly higher in hypoxia-acclimated fish but translated to marginal ecological benefits with an increase of ∼0.3 body lengths per second. Instead, hypoxia-acclimated fish may have relied more heavily on anaerobic metabolism during their swim trials, utilizing burst swimming 1.5 times longer than control fish. While the maintenance of CA-IV may still be an important contributor for hypoxia tolerance, our evidence suggests hypoxia-acclimated red drum are using other mechanisms to cope in an O2-depleted environment.

Oil and hypoxia alter DNA methylation and transcription of genes related to neurological function in larval Cyprinodon variegatus

DNA methylation is an important epigenetic mark involved in modulating transcription. While multiple studies document the ability of environmental stressors to alter methylation patterns, there is little information regarding the effects of oil and hypoxia on the methylome. Oil and hypoxic stress are threats in coastal ecosystems, which act as nursery habitats for developing fish. To explore the methylation altering effects of oil and hypoxia on developing fish, we exposed larval Cyprinodon variegatus to oil, hypoxia, or both for 48 h followed by 48 h of depuration in clean, normoxic conditions. We then used immunoprecipitation coupled with high-throughput sequencing (MeDIP seq) to evaluate genome-wide methylation changes. We also performed RNA seq to associate methylation and altered transcription. Oil and hypoxia together elicited greater impacts to methylation than either stressor individually. Additionally, the oil+hypoxia treatment exhibited an overlap between differentially methylated regions and differential gene expression at 20 loci. Functional analyses of these loci revealed enrichment of processes related to neurological function and development. Two neurological genes (slc1a2, asxl2) showed altered methylation of promoter CpG islands and transcriptional changes, suggesting epigenetic modulation of gene expression. Our results suggest a possible mechanism explaining altered behavior patterns noted in fish following oil exposure.

Brief Oil Exposure Reduces Fitness in Wild Gulf of Mexico Mahi-Mahi (Coryphaena hippurus)

The Deepwater Horizon (DWH) disaster released 3.19 million barrels of crude oil into the Gulf of Mexico (GOM) in 2010, overlapping the habitat of pelagic fish populations. Using mahi-mahi (Coryphaena hippurus)─a highly migratory marine teleost present in the GOM during the spill─as a model species, laboratory experiments demonstrate injuries to physiology and behavior following oil exposure. However, more than a decade postspill, impacts on wild populations remain unknown. To address this gap, we exposed wild mahi-mahi to crude oil or control conditions onboard a research vessel, collected fin clip samples, and tagged them with electronic tags prior to release into the GOM. We demonstrate profound effects on survival and reproduction in the wild. In addition to significant changes in gene expression profiles and predation mortality, we documented altered acceleration and habitat use in the first 8 days oil-exposed individuals were at liberty as well as a cessation of apparent spawning activity for at least 37 days. These data reveal that even a brief and low-dose exposure to crude oil impairs fitness in wild mahi-mahi. These findings offer new perspectives on the lasting impacts of the DWH blowout and provide insight about the impacts of future deep-sea oil spills.

Pyrene drives reduced brain size during early life exposure in an estuarine fish, the red drum (Sciaenops ocellatus)

Crude oil and the constituent polycyclic aromatic hydrocarbons (PAHs) induce a consistent suite of sub-lethal effects in early life stage fishes. It has been suggested that 3-ring PAHs drive cardiotoxicity and that all other impacts are downstream consequences of these cardiac effects. However, recent studies have documented behavioral alterations that may not be linked to cardiotoxicity. This raises the question of whether the 3-ring PAHs that drive cardiotoxicity are also responsible for the observed neurological impairments. To explore this question, we exposed embryonic red drum (Sciaenops ocellatus) - a species that exhibits greater sensitivity to craniofacial malformations than cardiotoxicity - to individual 2-ring, 3-ring, and 4-ring PAHs for 48 h after which they were assessed for sub-lethal developmental malformations. No effects were observed following exposure to naphthalene, anthracene, dibenzothiophene, phenanthrene and fluorene at doses equivalent to the ΣPAH₅₀ effective concentration 50 for craniofacial malformation in red drum. Conversely, pyrene caused complete lethality at the original dose, and a 5× diluted dose resulted in significantly reduced brain size and spine length. Similar sub-lethal effects were also observed in chrysene at the 1× dose. These results indicate that 4-ring PAHs are driving malformations in developing red drum and suggest oil induced impairments in this species are not a downstream consequence of 3-ring PAH induced cardiac malformations.

Effects of dispersant-treated oil upon behavioural and metabolic parameters of the anti-predator response in juvenile European sea bass (Dicentrarchus labrax)

Acute exposure to oil and oil dispersants can cause a wide range of physiological dysfunctions in marine fish species and evidences for consequences on behaviour are also increasing. In response to the presence of predators or to food availability, the modulation of locomotor activity and schools' behaviour enable fish to maximize their survival rates. However, the degree to which this regulatory process is affected by exposure to oil and/or dispersants is yet unknown. Here we investigated the effect of a 62-h experimental exposure to dispersant-treated oil on the behavioural (shoal cohesion, spontaneous activity) and metabolic (oxygen consumption) responses to simulated predation in juvenile European sea bass, Dicentrarchus labrax L. Our results suggest that exposure to petroleum hydrocarbons may affect negatively individual fitness through impaired ability to respond to predation. Shoal cohesion was not affected, but fish swimming activity was higher than control individuals under predation pressure and the amplitude of their metabolic response was significantly reduced. Fish recovered from alteration of their metabolic response 7 days post-exposure. Additionally, a strong habituation component was observed in C fish and the absence of such pattern in E fish suggest altered capacity to habituate over time to the surrounding environment and possible impairments of the related cognitive performances. Altogether, our data show that juvenile sea bass exposed to oil exhibit transient physiological dysfunctions and impairments of complex behaviours that may have major population-level consequences.