Ciguatera is a foodborne disease caused by ciguatoxins (CTXs), produced by dinoflagellates (genera Gambierdiscus and Fukuyoa), which bioaccumulate in fish through the food web, causing poisoning in humans. Currently, the physiological mechanisms of the species with the highest amount of toxins in their adult stage of life that are capable of causing these poisonings are poorly understood. Dusky grouper (Epinephelus marginatus) is a relevant fishing species and is part of the CTX food chain in the Canary Islands. This study developed an experimental model of dietary exposure featuring adult dusky groupers with two diets of tissue naturally contaminated with CTXs (amberjack and moray eel flesh) with two different potential toxicities; both groups were studied at different stages of exposure (4, 6, 10, 12, and 18 weeks). The results showed that this species did not show changes in its behavior due to the provided feeding, but the changes were recorded in biochemical parameters (mainly lipid and hepatic metabolism) that may respond to liver damage and alterations in the homeostasis of the fish; more research is needed to understand histopathological and cytotoxic changes.

Seriola dumerili is a fast-growing species under culture conditions with significant potential for diversification of marine aquaculture. The interest in this species raises new challenges for its culture, such as the design of suitable procedures and appropriate conditions in order to determine the adequate operational parameters for animal welfare, which will also allow the generation of management protocols that guarantee these conditions. These parameters include stocking density and photoperiod, which can be decisive in the welfare of the farmed fish. Therefore, the overall objective of this study was to investigate the combined effect of different culture conditions (stocking density and photoperiod) on different biochemical indicators of stress, including plasma and skin mucus parameters, immune response, oxidative damage and antioxidant response in S. dumerili. Adult specimens were divided into four groups and maintained under two stocking densities (2.5 kg m^-³ and 5.0 kg m^-³) and two photoperiods (12L:12D and 16L:8D) (n=9 for each condition). The results showed that after 30 days, there were no negative effects on the growth performance of fish stocked at higher density or long photoperiod. There were also no changes in plasma stress markers or immune parameters. However, under long photoperiod, higher cortisol levels were found in skin mucus, along with alterations in antioxidant activities in key tissues such as liver or gills, as well as, lipid peroxidation in liver, brain and muscle, indicating some degree of oxidative stress. In contrast, variations in different stocking densities did not lead to significant alterations in these parameters. This study offers new insights into the mechanisms involved in the stress response of S. dumerili, aiming to evaluate different culture conditions and determine stress-inducing factors for this species.

The aquaculture of Octopus vulgaris is gaining interest due to its high demand, rapid growth, and nutritional value. However, significant challenges remain, particularly in rearing paralarvae to juveniles, mainly due to their specific nutritional needs. This study evaluates the impact of two bioactive compounds— Hytolive^® syrup (natural olive fruit extract rich in hydroxytyrosol) and black cumin seed oil (rich in thymoquinone)— using Artemia as a vector, on growth performance, fatty acid profiles, antioxidant responses and lipid peroxidation in O. vulgaris paralarvae from 0 to 30 days post-hatch (dph). Paralarvae were fed one of three diets: control diet (Artemia metanauplii enriched with marine lecithin, CON), control diet supplemented with 10% of Hytolive^® syrup (HYT), or control diet supplemented with 30% black cumin seed oil (BCO), with three replicates per treatment. While no significant differences were observed in specific growth rates (SGR) or survival, the HYT and BCO groups exhibited reduced lipid peroxidation at 30 dph, indicating enhanced antioxidant defenses. Additionally, bioactive supplementations altered fatty acid profiles, increasing polyunsaturated fatty acids compared to the control. Although enzymatic antioxidant responses such as catalase (CAT) and superoxide dismutase (SOD) were unaffected, glutathione S-transferase (GST) activity significantly decreased in the BCO group, suggesting a reduced need for detoxification due to lower oxidative stress. This study is the first to demonstrate the transfer of hydroxytyrosol and thymoquinone metabolites from Artemia to O. vulgaris paralarvae and their potential to mitigate oxidative stress. These findings highlight the potential benefits of bioactive-enriched diets in octopus aquaculture and their protective effects during early development. Future research should explore optimal dosages and synergies between bioactive compounds to enhance the immune system and overall health of this species.