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Methionine (MET) supplementation is a current strategy to achieve shrimp requirement. Notwithstanding, the efficiency of the precisely formulated feeds can be diminished since shrimps are slow eaters and masticate feed externally which results in nutrient leaching. In this regard, a methionine dipeptide (DL-Methionyl DL-Methionine) benefits the feed industry by reducing MET water solubility while increasing its bioavailability. Therefore, the effects of feeding whiteleg shrimp (Penaeus vannamei) with increasing levels of methionine dipeptide was evaluated on zootechnical performance and methionine-, immune- and antioxidant- related pathways. A 74 days growth trial was conducted by feeding a control diet and four diets supplemented with AQUAVI® Met-Met at 0.08, 0.12, 0.24 and 0.32% of DM. Diet digestibility, body AA composition and nitrogen metabolites, metabolic enzymes, oxidative status and gene expression were evaluated. It can be concluded that graded dietary increase of methionine dipeptide up to 0.24 % for 74 days translated in significant gains on the growth performance, feed efficiency, nutrient and nitrogen gain and shrimp survival. Moreover, it was showed that Met-Met dietary spare leads to an improvement of free-AA pool and nitrogen metabolites concentration and reduces the signs of oxidative stress. Finally, in a closer look to the MET-related pathways passive to be altered by Met-Met spare, a clear modulation of the described antioxidant and cell proliferation routes was detected.

Several feed additives have proved to be beneficial in eliciting fish health. Β-glucans and curcumin are compounds with immunomodulatory capacities known to increase growth performance, stimulate immunity, improve general health, and enhance disease resistance in fish. The present study aimed to evaluate the effects of dietary Phaeodactylum tricornutum extracts rich in β-glucans and curcumin on gilthead seabream health status prior to and following an intestinal inflammatory stimulus. Three experimental diets were formulated: a practical commercial-type diet (CTRL), a CTRL diet supplemented with 1% microalgae-derived β-glucans extract (BG), and a CTRL diet supplemented with 0.2% of curcumin (CUR). After 30 days of the feeding trial, fish were sampled and subjected to an oral administration of 1% dextran sodium sulphate (DSS) to induce intestinal inflammation. Four groups were considered: a group of fish continued to be fed on the CTRL diet while the remaining groups were exposed to DSS, including CTRL-D (CTRL + DSS), BG-D (BG + DSS), and CUR-D (CUR + DSS), for 6 days. Growth, plasma and gut humoral immunity, liver and gut oxidative stress biomarkers, and intestinal gene expression were evaluated. No significant differences were found in growth after 30 days of feeding; however, seabream fed BG had decreased anti-protease activity and nitric oxide concentration in plasma while those fed CUR had increased mRNA levels of the tnfα, csf1r, and hep genes compared to those fed CTRL. After the inflammatory stimulus, hematocrit was enhanced in fish fed BG-D and CUR-D while red blood cell counts increased in those fed CTRL-D. Superoxide dismutase activity decreased in the intestine of all DSS groups while lipid peroxidation increased in the gut of fish fed CTRL-D and BG-D compared to CTRL. Moreover, the mRNA expression levels of csfr1 and sod decreased in fish fed CTRL-D and BG-D compared to CTRL, respectively. Despite the mild intestinal inflammatory condition induced by DSS, CUR was able to partially ameliorate its effects, improving the hematological profile and assisting against the oxidative stress.

Probiotic bacteria have been widely studied in the past few decades as an efficient alternative to the existing methods of preventing disease outbreaks. Most commercial probiotics used in animal husbandry are non-native species that may fail to colonize the target habitat of the host. After rectal administration to maximise colonization by-passing digestion in the stomach, the beneficial effects of two native probiotics Psychrobacter nivimaris and Psychrobacter faecalis on the immune status, inflammatory response, and disease resistance against Tenacibaculum maritimum were studied in juvenile turbot. After an experimental infection with T. maritimum (bath of 2.65 × 107 CFU mL− 1), selected immune markers (mhc II α, il-1β, tcr, tgf β and tnf α) were determined by RT-QPCR at 0, 1 and 5 days post infection (dpi). Treatment with P. nivimaris and P. faecalis resulted in 0% and 8% mortalities (n = 3). In the treatment control, an elevated mortality of 20% was observed. In the challenge controls (no infection), no mortalities were observed during the experimental period. At 0 dpi, gene expression was comparable between the treatments and the treatment control, suggesting that probiotics did not act via immune stimulation of the host but rather via competitive exclusion of the pathogen. At 1 dpi, gene expression of all genes was up-regulated only in the treatment control, showing that the infection in probiotic-supplemented fish progressed in a milder way. At 5 dpi, gene expression returned to baseline levels, and no significant differences were observed between groups. After 1 dpi, no mortalities were observed. As a conclusion, the native probiotic candidates P. nivimaris and P. faecalis improved survival, whereas, in the control, mortality increased and expression of selected immune markers was up-regulated upon experimental infection with T. maritimum. This highlights a potential application of P. nivimaris and P. faecalis in disease prophylaxis.