Melatonin production improves Senegalese sole sperm motility at night, but fails as a supplement during cryopreservation.

Melatonin is a powerful antioxidant present in fish seminal plasma. This study aimed to understand melatonin's endogenous and exogenous effects on first-generation Senegalese sole sperm quality for sperm management applications. In the first experiment, samples were collected at mid-light (ML) and mid-dark (MD) daytimes, to evaluate the effects on sperm motility. In a second experiment, using confocal microscopy and melatonin-FITC, spermatozoa permeability to melatonin was evaluated and, after showing that it enters the nucleus and mitochondria by passive diffusion, exogenous melatonin toxicity and antioxidant potential during a cryopreservation assay were performed. The toxicity assay tested different melatonin concentrations (0.01, 0.1, 1, and 10 mM) and exposure times (3, 5, 15 and 30 min), and sperm motility parameters were measured (TM, PM, VCL, VSL, LIN) using CASA system. The best conditions (0.1 and 10 mM) were selected for the cryopreservation assay, and a set of post-thaw sperm quality analyses were performed (motility, viability, reactive oxygen species, lipid peroxidation, and DNA fragmentation). The motility analyzed at ML and MD showed significant differences in all parameters, mainly on velocities (VCL, VSL, VAP), that were significantly higher at MD. Supplemented melatonin did not influence spermatozoa motility, MDA content or DNA fragmentation, although a lower percentage of viable cells was obtained on the 10 mM treatment. Altogether, Senegalese sole spermatozoa motility was enhanced at night, putatively by endogenous melatonin through direct or indirect mechanisms, whereas supplemented melatonin did not confer extra protection during cryopreservation.

Ex vivo exposure to titanium dioxide and silver nanoparticles mildly affect sperm of gilthead seabream (Sparus aurata) - A multiparameter spermiotoxicity approach.

Nanoparticles (NP) are potentially reprotoxic, which may compromise the success of populations. However, the reprotoxicity of NP is still scarcely addressed in marine fish. Therefore, we evaluated the impacts of environmentally relevant and supra environmental concentrations of titanium dioxide (TiO2: 10 to 10,000 µg·L-1) and silver NP (Ag: 0.25 to 250 µg·L-1) on the sperm of gilthead seabream (Sparus aurata). We performed short-term direct exposures (ex vivo) and evaluated sperm motility, head morphometry, mitochondrial function, antioxidant responses and DNA integrity. No alteration in sperm motility (except for supra environmental Ag NP concentration), head morphometry, mitochondrial function, and DNA integrity occurred. However, depletion of all antioxidants occurred after exposure to TiO2 NP, whereas SOD decreased after exposure to Ag NP (lowest and intermediate concentration). Considering our results, the decrease in antioxidants did not indicate vulnerability towards oxidative stress. TiO2 NP and Ag NP induced low spermiotoxicity, without proven relevant ecological impacts.

Cognitive appraisal in fish: stressor predictability modulates the physiological and neurobehavioural stress response in sea bass.

The role of cognitive factors in triggering the stress response is well established in humans and mammals (aka cognitive appraisal theory) but very seldom studied in other vertebrate taxa. Predictability is a key factor of the cognitive evaluation of stimuli. In this study, we tested the effects of stressor predictability on behavioral, physiological and neuromolecular responses in the European sea bass (Dicentrarchus labrax). Groups of four fish were exposed to a predictable (signalled) or unpredictable (unsignalled) stressor. Stressor predictability elicited a lower behavioural response and reduced cortisol levels. Using the expression of immediate early genes (c-fos, egr-1, bdnf and npas4) as markers of neuronal activity, we monitored the activity of three sea bass brain regions known to be implicated in stressor appraisal: the dorsomedian telencephalon, Dm (putative homologue of the pallial amygdala); and the dorsal (Dld) and ventral (Dlv) subareas of the dorsolateral telencephalon (putative homologue of the hippocampus). The activity of both the Dm and Dlv significantly responded to stressor predictability, suggesting an evolutionarily conserved role of these two brain regions in information processing related to stressor appraisal. These results indicate that stressor predictability plays a key role in the activation of the stress response in a teleost fish, hence highlighting the role of cognitive processes in fish stress.