Fatty acid-sensing mechanisms in the hypothalamus of European sea bass (Dicentrarchus labrax): The potential role of monounsaturated and polyunsaturated fatty acids.

This study aimed to evaluate the hypothalamus fatty acid (FA)-sensing mechanisms response to different FA in European sea bass. For that purpose, fish (body weight of 90 g) were intraperitoneally (IP) injected (time 0 h) with five long-chain unsaturated fatty acids, namely, docosahexaenoic acid (DHA; C22:5n3); eicosapentaenoic acid (EPA; C20:4n3); α-linolenic (ALA; C18:3n3); linoleic acid (LA; C18:2n6) and oleic acid (OA; C18:1n9) at a dose of 300 µg kg-1, or with 0.9% saline solution (control). Feed intake (FI) was recorded at 3, 6, and 24 h after the IP injection. One week later, fish were IP injected with the same FA, and the hypothalamus was collected 3 h after the IP injection for measurement of molecules related to FI regulation and FA-sensing mechanisms. Cumulative FI (g/kg/day) was not affected by treatments. However, compared to the control, FI increased with the OA treatment at 6 h after the IP injection. FI decreased with mealtime in the DHA and LA groups. Gene expression of orexigenic (npy/agrp) and anorexigenic (cart2/pomc1) neurons was not affected by the FA treatments. Attending the enzymes involved in the FA-sensing mechanisms activation, compared to the control carnitine palmitoyltransferase I (CPT1) and ATP citrate lyase (ACLY) activity were not affected by FA treatments. Contrarily the key enzymes of lipid metabolisms, malic enzyme and hydroxyacylCoA dehydrogenase was higher in fish that received the EPA and OA treatment, than fish treated to the control. Overall, the results of the present study indicate that gene expression of orexigenic and anorexigenic neurons was not affected at 3 h after IP injection with different FA. However, the activity of key enzymes of lipid metabolism was differently affected by circulating FA, indicating that FA-sensing mechanisms respond to different FA. Further studies are required involving different sampling times to further characterize the response of FA-sensing mechanisms to FA. These findings may be of relevance to the aquaculture industry in an era where alternative lipid sources are being increasingly used.

Taurine modulates hepatic oxidative status and gut inflammatory markers of European seabass (Dicentrarchus labrax) fed plant feedstuffs-based diets.

This study aimed to evaluate the effect of taurine (tau) supplementation to low fishmeal (FM) diets on growth performance, oxidative status, and immune response of European seabass juveniles. Four isoproteic (46% crude protein) and isolipidic (19% crude lipid) diets were formulated to contain either 25 or 12.5% FM and a mixture of plant feedstuffs, supplemented or not with 1% tau. Twelve groups of 20 fish (IBW = 9.4 g) were fed each diet for 9 weeks. Reduction of dietary FM from 25 to 12.5% impaired growth performance, feed efficiency, and protein efficiency ratio but had no effect on nitrogen retention (% N intake). Independently of FM level, dietary tau supplementation improved growth performance and nitrogen retention without affecting feed efficiency. Dietary FM level reduction increased liver G6PDH activity, but did not affect lipid peroxidation or activities of redox key enzymes. Contrarily, dietary tau supplementation decreased hepatic G6PDH and GPX activities and lipid peroxidation. Gene expression COX-2 was not affected either by FM or tau levels but TNF-α increased with the reduction of FM level but not with the tau level. Dietary tau supplementation decreased Casp3 and Casp9 expression regardless of dietary FM level. Overall, this study evidenced that dietary tau supplementation improved growth performance and antioxidant response and reduced intestine inflammatory and apoptosis processes.