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Global change produces substantial modification to the distribution and rhythm of infection of diseases in fish, favouring the introduction of new pathogens. Recently, the presence of black spot disease, associated with a digenean fluke of the genus Scaphanocephalus, has been observed in specimens of Xyrichthys novacula on the island of Ibiza (Balearic Islands). The aim of the present study was to evaluate the antioxidant and immune response in both the skin mucus and spleen of X. novacula depending on the degree of infection by Scaphanocephalus sp. The specimens were captured in a control area, without the presence of the parasite, and in an affected area, classifying the fish as low infection (1–15 spots) and high infection (>15 spots). As the degree of infection increased, a decrease in the body condition index was observed. The activity of the antioxidant enzymes in the mucus—catalase, superoxide dismutase and glutathione peroxidase—increased progressively with the degree of infection. This activation of antioxidant defences was not enough to prevent an increase in malondialdehyde levels, an indicator of oxidative damage, in the group with the highest infection. Similarly, an increase in immunological parameters—lysozyme, alkaline phosphatase, myeloperoxidase and immunoglobulins—was observed in mucus as infection increased. Regarding the spleen, only an increase in lysozyme activity and alkaline phosphatase in fish with a greater severity of infection was observed. In conclusion, as the severity of Scaphanocephalus sp. infection increased, it induced an immune and oxidative stress response in skin mucus, leading to a decrease in overall body condition. The potential health effects that the ectoparasite may have on X. novacula populations will require follow-up studies. Full article

Recent technological advances in marine biotelemetry have demonstrated that marine fish species perform activity–rest rhythms that have relevant ecological and evolutionary consequences. The main objective of the present report is to study the circadian rhythm of activity–rest of the pearly razorfish, Xyrichtys novacula in its own habitat, before and during the reproduction season using a novel biotelemetry system. This fish species is a small-bodied marine species that inhabits most shallow soft habitats of temperate areas and has a high interest for commercial and recreational fisheries. The activity of free-living fish was monitored by means of high-resolution acoustic tracking of the motor activity of the fish in one-minute intervals. The obtained data allowed the definition of the circadian rhythm of activity–rest in terms of classical non-parametric values: interdaily stability (IS), intradaily variability (IV), relative amplitude (RA), average activity during the most-active period of consecutive 10 h (M10), and average activity during the least-active period of consecutive 5 h (L5). We observed a well-marked rhythm, with little fragmentation and good synchrony with the environmental cycle of light–darkness, regardless of sex and the period studied. However, the rhythm was found to be slightly more desynchronized and fragmented during reproduction because of variations in the photoperiod. In addition, we found that the activity of the males was much higher than that of the females (p < 0.001), probably due to the peculiar behavior of the males in defending the harems they lead. Finally, the time at which activity began in males was slightly earlier than it was in females (p < 0.001), presumably due to the same fact, as differences in activity or for the individual heterogeneity of this species in the time of awakening are considered to be an independent axis of the fish’s personality. Our work is novel, as it is one of the first studies of activity–rest rhythm using classical circadian-related descriptors in free-living marine fish using locomotory data facilitated by novel technological approaches. Full article

Plastic pollution in the oceans is a growing problem, with negative effects on exposed species and ecosystems. Xyrichtys novacula L. is a very important fish species both culturally and economically in the Balearic Islands. The aim of the present study was to detect and categorise the presence of microplastics (MPs) in the digestive tract of X. novacula, as well as the existence of oxidative stress in the liver. For this purpose, the fish were categorised into two groups based on the number of MPs observed in the digestive tracts: a group with no or low presence of MPs (0–3 items) and a group with a higher presence of MPs (4–28 items). MPs were found in 89% of the specimens analysed, with a dominance of fibre type and blue colour. Regarding the type of polymer, polycarbonate was the most abundant, followed by polypropylene and polyethylene. For the group with a greater presence of MPs, the activities of the antioxidant enzymes glutathione peroxidase and glutathione reductase, as well as the phase II detoxification enzyme glutathione s-transferase, were higher than the activities observed in fish with little to no presence of MPs. The activities of catalase and superoxide dismutase and the levels of malondialdehyde did not show significant differences between both groups. In conclusion, these results demonstrate the presence of MPs in the digestive tract of X. novacula and the existence of an antioxidant and detoxification response, mainly based on the glutathione-based enzymes. Full article