Effect of seaweed supplementation on growth performance, immune and oxidative stress responses in gilthead seabream (Sparus aurata)

Seaweeds have important nutraceutical properties, including antioxidant and biological response-modifying qualities. Their dietary supplementation may increase the immune and antioxidant capacity of fish necessary to cope to stressful conditions and minimizing disease outbreaks. There are essentially four major groups of seaweed that can be classified by color, namely green (Chlorophyta), brown/yellow (Phaeophyta), red (Rhodophyta), and blue-green (Cyanophyta). Some green seaweed has active radical scavenging properties. Red and brown have bioactive compounds that play a vital role as antihypertensive and antioxidant. The current study was designed to evaluate the effects of seaweed supplementation on growth performance, immune and oxidative stress responses in gilthead seabream (Sparus aurata). Three seaweed species, each from one of the following groups, Rhodophyta (R), Phaeophyta (P) and Chlorophyta (C), were supplemented to the experimental diets at 2.5% and 7.5% and tested against a control diet (Ctrl) with no supplementation. In addition to six diets with seaweed in two different levels of supplementation: R2.5%, P2.5%, C2.5%, R7.5%, P7.5% and C7.5%; a diet with a mix (M), supplemented at 7.5% (2.5% of each algae) was also tested. A total of 360 seabream fingerlings, 13.07 ± 0.13cm and 31.17 ± 0.63g were allocated in 24 rectangular tanks, 115L capacity each, with a 4L/min water output connected to a recirculation seawater system. Fish were fed twice a day until satiation and water quality (temperature: 20.5 ºC; D.O.: 8.13 mg/L; Ammonia: 0.5 mg/L Nitrite: 0.5 mg/L) were daily monitored. At day 40 of the trial, an intermediate sampling was carried out. Standard zootechnical parameters were measured for the growth performance determination. In addition, blood, liver and intestine samples were collected for the evaluation of the immune (lysozyme and peroxidase) and oxidative stress (lipid peroxidation, glutathione peroxidase, glutathione reductase, total glutathione and catalase) responses and digestive capacity (amylase, chymotrypsin, trypsin and lipase). Growth performance parameters showed no significant difference, but all supplemented treatments tended to have better results than control. Plasma peroxidase was improved by dietary seaweed supplementation. Plasm lysozyme increased in R7.5% group when compared to the other dietary groups (Table 1). Amylase, chymotrypsin and trypsin had low activity, while lipase had higher activity. Catalase, glutathione peroxidase, glutathione reductase and glutathione s-transferase were not statistically different among the dietary treatments. Nevertheless, these enzymes tended to have higher activity on supplemented treatments than control. Total glutathione and lipid peroxidation were significantly higher in R2,5% and, R7,5% and M, respectively (Table 1). Results indicate seaweed supplementation may improve immune and antioxidant responses in gilthead seabream. Further studies are needed in order to access the protective effects of dietary seaweed supplementation in fish subjected to stress conditions.