Shoaling Behavior in Zebrafish
This work evaluated the potential of a volatile oil extracted from Syagrus coronata seeds for the control of Aedes aegypti. The oil was extracted by hydrodistillation, characterized by gas chromatography-mass spectrometry (GC-MS), and evaluated for larvicidal and ovicidal activities, as well as for influence on the choice of oviposition site by females. The effects of the oil on swimming activity of larvae were also investigated. The oil extraction showed a yield of 0.41% and GC-MS revealed that 98.42% of the composition corresponded to the following fatty acids: octanoic acid (40.55%), decanoic acid (17.39%) and dodecanoic acid (40.48%). The oil promoted the death of A. aegypti larvae, with LC50 of 21.07 ppm, but had no ovicidal action. The octanoic, decanoid and dodecanoic acids showed larvicidal activity with LC50 of 51.78, 24.01 and 19.72 ppm, respectively. The swimming activity of larvae incubated with the oil during 1 and 3 h was significantly (p < 0.05) lower than that of control (0.2% Tween 80, v/v) larvae. The S. coronata oil and the octanoic acid (both at 50 ppm) showed a deterrent effect on oviposition. In conclusion, the essential oil of S. coronata seed was able to promote death of A. aegypti larvae and exerted a deterrent effect on pregnant females. The results indicated that the larvicidal activity is due to the action of decanoic and dodecanoic acids while the oviposition deterrent effect is probably linked to the presence of octanoic acid.
Zebrafish: an animal model for toxicological studies
Antibiotics are among the most extensively used pharmaceuticals worldwide. They are natural or synthetic drugs with the capacity to kill or inhibit the growth of microorganisms. Several antibiotics have been detected in aquatic environments, but little is known about their effects on non-target organisms, especially fish. The aim of this study was to evaluate the effects of the antibiotic nitrofurantoin (NTF) using zebrafish embryos as model organisms. To assess mortality and development effects, the embryos were exposed to 0, 4, 9, 44, 100, 223 and 500 mg/L of NTF. A sub-lethal range of concentrations (0, 0.001, 0.02, 0.32, 5.62 and 100 mg/L) was used for biomarker analyses, namely cholinesterase, lactate dehydrogenase, glutathione S-transferase and catalase. The results indicated low toxicity of NTF to zebrafish, with a 168 h-LC50 value of 129.2 mg/L. The main effect on development was the loss of equilibrium related to the uninflated swim bladder (168 h-EC50 = 96.72 mg/L). Biomarker activity was induced in concentrations as low as 0.02 mg/L (cholinesterase, lactate dehydrogenase, glutathione S-transferase). Exposure to NTF induced no significant effects on zebrafish larvae behaviour. In summary, short-term exposure of zebrafish embryos to NTF induced developmental alterations only at high concentrations. However, biochemical changes occurred at lower levels of exposure, suggesting long-term effects on fish populations.
Aggression is a behavioural trait characterized by the intention to harm others for offensive or defensive purposes. Neurotransmitters such as serotonin and dopamine are important mediators of aggression. However, the physiological role of the histaminergic system during this behaviour is currently unclear. Here, we aimed to better understand histaminergic signalling during aggression by characterizing the involvement of the histamine H3 receptor (Hrh3).
We have generated a novel zebrafish Hrh3 null mutant line using CRISPRCas9 genome engineering and investigated behavioural changes and alterations to neural activity using whole brain Ca2+ imaging in zebrafish larvae and ribosomal protein S6 (rpS6) immunohistochemistry in adults.
We show that genetic inactivation of the histamine H3 receptor (Hrh3) reduces aggression in zebrafish, an effect that can be reproduced by pharmacological inhibition. In addition, hrh3−/− zebrafish show behavioural impairments consistent with heightened anxiety. Larval in vivo whole brain Ca2+ imaging reveals higher neuronal activity in the forebrain of mutants, but lower activity in specific hindbrain areas and changes in measures of functional connectivity between subregions. Adult hrh3−/− zebrafish display brain region-specific neural activity changes in response to aggression of both key regions of the social decision-making network, and the areas containing histaminergic neurons in the zebrafish brain.
These results highlight the importance of zebrafish Hrh3 signalling for aggression and anxiety and uncover the brain areas involved. Targeting this receptor might be a potential novel therapeutic route for human conditions characterized by heightened aggression.
Link to the publication :
Aquaculture and Fisheries