Hypocretins/Orexins neuropeptides are known to regulate numerous physiological functions, such as energy homeostasis, food intake, sleep/wake cycle, arousal and wakefulness, in vertebrates. Previous studies on mice have revealed an intriguing orexins/endocannabinoids (ECs) signaling interaction at both structural and functional levels, with OX-A behaving as a strong enhancer of 2-arachydonoyl-glycerol (2-AG) biosynthesis. In this study, we describe, for the first time in the brain of zebrafish, the anatomical distribution and co-expression of orexin (OX-2R) and endocannabinoid (CB1R) receptors, suggesting a functional interaction. The immunohistochemical colocalization of these receptors by confocal imaging in the dorsal and ventral telencephalon, suprachiasmatic nucleus (SC), thalamus, hypothalamus, preoptic area (PO) and cerebellum, is reported. Moreover, biochemical quantification of 2-AG levels by LC-MS supports the occurrence of OX-A-induced 2-AG biosynthesis in the zebrafish brain after 3 h of OX-A intraperitoneal (i.p.; 3 pmol/g) or intracerebroventricular (i.c.v.; 0.3 pmol/g) injection. This effect is likely mediated by OX-2R as it is counteracted by i.p./i.c.v administration of OX-2R antagonist (SB334867, 10 pmol/g). This study provides compelling morphological and functional evidence of an OX-2R/CB1R signaling interaction in the brain of adult zebrafish, suggesting the use of this well-established vertebrate animal model for the study of complex and phylogenetically conserved physiological functions.

The present study aimed to investigate the effect of Foeniculum vulgare essential oil on the health of the common carp (Cyprinus carpio). A total of 120 healthy fish were provided with feed containing 200, 400, and 600 mg/kg of F. vulgare oil for 60 days. Findings revealed that the oral administration of 200 mg/kg of F. vulgare oil significantly increased final weight, weight gain, and specific growth rate compared to the control group (p < 0.05). Plasma biochemical enzyme levels remained unchanged in 200 and 400 mg/kg treatments, whereas they were found to be significantly increased in treatments with 600 mg/kg. Although no significant alterations in glucose, triglyceride, and cholesterol levels were observed, the treated groups exhibited significant increases in total protein, albumin, globulin, and creatinine levels. Results also indicated significantly decreasing levels of glutathione peroxidase, whereas superoxide dismutase activity increased. The gonadosomatic index showed notable improvement in the 200 and 400 mg/kg groups. Furthermore, plasma concentrations of estradiol and testosterone were significantly affected by doses of 400 and 200 mg/kg. Findings suggest that, following the administration of F. vulgare extract, the reproductive and general health of the fish appears to be improved. Nevertheless, it is recommended to supplement fish diets with up to 200 mg/kg of F. vulgare extract to improve their reproductive and general health. Concentrations above this limit can potentially cause harm.