Tryptophan participates on several physiological mechanisms of the neuroendocrine-immune network and plays a critical role in macrophages and lymphocytes function. This study intended to evaluate the modulatory effects of dietary tryptophan on the European seabass (Dicentrarchus labrax) immune status, inflammatory response and disease resistance to Photobacterium damselae piscicida. A tryptophan deficient diet (NTRP); a control diet (CTRL); and two other diets supplemented with tryptophan at 0.13% (TRP13) and 0.17% (TRP17) of feed weight were formulated. Fish were sampled at 2 and 4 weeks of feeding and the remaining were i.p. injected with Phdp (3 × 10⁶ cfu/fish) at 4 weeks and the inflammatory response (at 4, 24, 48 and 72 hours post-infection) as well as survival were evaluated. Results suggest that fish immune status was not altered in a tryptophan deficient scenario whereas in response to an inflammatory insult, plasma cortisol levels increased and the immune cell response was compromised, which translated in a lower disease resistance. When dietary tryptophan was offered 30% above its requirement level, plasma cortisol increased and, in response to bacterial infection, a decrease in lymphocytes, monocytes/macrophages and several immune-related genes was observed, also compromising at some degree fish disease resistance.

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.

Atlantic salmon (Salmo salar L.) are an emblematic anadromous fish species that inhabit marine and freshwater ecosystems in the Northern Hemisphere. In Portugal, the southern limit of its global distribution range, the species is classified as Critically Endangered (CR), and occurs only in the Minho and Lima rivers, which hold the most abundant populations, with occasional confirmed occurrences in the Cávado and Douro rivers. In this region, the species faces several highly detrimental threats (e.g., dams and other obstacles, unsuitable fishing legislation, and climate change), but some knowledge gaps about the biology, ecology, and structure of these southern populations often impair any attempt to define and implement effective management and conservation programs. We present the objectives, actions, and preliminary results of a set of projects and partnerships, recently implemented in Portugal, focused on increasing knowledge about local salmon populations to contribute to the development of suitable management guidelines for the target species. Within the project “SALMONLINK—Contribution of scientists and fishermen to the conservation and participatory management of Atlantic salmon populations in Portugal”, several actions have been implemented for the past three years to improve knowledge about this species, including the assessment of salmon distribution and abundance, adult and juvenile migration patterns, and population structure. In complement to these measures, we are also implementing (in Portugal) the international projects “SMOLTrack III & IV—Quantifying smolt survival from source to sea: informing management strategies to optimize returns”, which are specifically focused on smolt seaward migration and aim to obtain more information on this particularly vulnerable life-stage. Combined with a strong link with the local commercial and recreational fishing communities, who are providing data on salmon catches and contributing to an overview of the socioeconomic value of salmon in Portugal, these projects will contribute to increasing the knowledge of these populations, and at the same time, within the context of the constant transfer of knowledge between all the involved parties, advise the adaptation of the current fishing legislation to the conservation and management requirements of this highly endangered species.

The brown trout (Salmo trutta L.) is one of the most iconic native species from European river ecosystems and is also one of the main species of interest for recreational fishing activities (e.g., fly fishing). This species has a significant potential to attract anglers and related investment to the main fishing grounds, which are usually located in poorly developed areas and away from main city centers. Due to its environmental and socioeconomic value, this species is often targeted by management programs directed to the protection and sustainable exploitation of this valuable natural resource. One of the most common actions to enhance the abundance and condition of trout populations is the restocking of wild populations with fish from aquaculture facilities. However, most fish come from fishfarms using production methods such as high densities in the tanks, use of commercial food and standardized feeding methods, lack of environmental stimulus, and domestication of breeding stocks, which usually results in poor fitness and very low survival rates after release. This consequently leads to reduced success of these management actions. To contribute to solving these problems and enhancing the success of restocking actions for the recovery and sustainable enhancement of wild trout populations, we propose a novel approach to the production of this species, by testing and implementing a new protocol that aims to produce wild-reared trout. These fish come from wild breeders and will be produced with the least human contact in conditions that mimic their natural habitat. Taking advantage of a recently remodeled and re-equipped aquaculture facility, located in Central Portugal (Posto Aquícola de Campelo, Figueiró dos Vinhos), we are rearing trout in low densities (10–20 trout/m³), like the ones observed in natural habitats, using live food (larvae and insects), and subjected to environmental stimuli such as refuges, and water and flow variability, equivalent to those observed in local streams. Accompanied by a pre- and post-restocking monitoring program (e.g., evaluation of trout abundances and habitat in the target stream, dispersion and movement patterns and survival), this study will contribute to enhancing the success of future restocking actions, promoting the sustainable enhancement of wild trout populations, and, thus, increasing the interest of restocked fishing grounds for angling activities and associated incomes.