Nutrition and farming practices as modulators of quality in gilthead seabream (Sparus aurata)

Gilthead seabream is the most important farmed species in the Mediterranean, and knowledge on how common farming practices impact its quality is limited. As such, this Thesis aimed to evaluate how gilthead seabream flesh quality is affected by some of these practices. In Chapter 2, the influence of nutritional factors was evaluated, specifically the high replacement of traditional marine-derived ingredients, both fishmeal and fish oil, with vegetable sources. We have seen that the vegetable-based diets tested did not greatly impact seabream flesh quality, although some alterations were seen in the fatty acid profile of the muscle. However, and despite having caused no alterations in flesh texture, vegetable ingredients reduced the amount of sulphated glycosaminoglycans in the extracellular matrix, affected muscle pH and reduced the activity of proteolytic enzymes. Throughout this Thesis, we measured for the first time the activity of proteolytic enzymes in seabream muscle, and cathepsin B was found to play a pivotal role in post-mortem muscle degradation. In Chapter 3, we evaluated the effect of harvesting and slaughter stress on seabream quality, and contrary to what is seen in most farmed species, our results show that gilthead seabream muscle structure is highly resistant to changes caused by stressful events. Nonetheless, considering that welfare is an increasingly important quality criterion, the use of a zero-withdrawal anaesthetic as a rested harvest technique or even slaughter method could prove valuable to the industry. In Chapter 4, we used maslinic acid as a dietary supplement, to modulate the muscle’s energetic status pre-mortem. As a finishing strategy, maslinic acid failed to increase levels of glycogen and ATP in the muscle. However, supplementation resulted in higher muscle fibre diameter and lower cathepsin B activity, and maslinic acid is likely to be useful to promote growth in this species. In general our Thesis has generated new knowledge to a major challenge facing the aquaculture industry, which is to find a compromise between the trends towards intensive rearing and consumer demand for healthy, high quality seafood being ethically acceptable and having a low impact on the environment.

Screening for biological activities with application in aquaculture in halophytes from the Algarve coastline

Infectious diseases often hamper the production of aquatic organisms in aquaculture systems, causing economical losses, environmental problems and consumer safety issues. The conventional way aquaculture producers had to control pathogens was by means of synthetic antibiotics and chemicals. This procedure had consequences in the emergence of more resilient pathogens, drug contamination of seafood products and local ecosystems. To avoid the repercussions of antibiotic use, vaccination has greatly replaced human drugs in western fish farms. However there is still massive unregulated antibiotic use in third world fish farms, so less expensive therapeutic alternatives for drugs are desperately needed. An alternative way to achieve disease control in aquaculture is by using natural bioactive organic compounds with antibiotic, antioxidant and/or immunostimulant properties. Such diverse biomolecules occur in bacteria, algae, fungi, higher plants and other organisms. Fatty acids, nucleotides, monosaccharides, polysaccharides, peptides, polyphenols and terpenoids, are examples of these substances. One promising source of bioactive compounds are salt tolerant plants. Halophytes have more molecular resources and defence mechanisms, when compared with other tracheophytes, to deal with the oxidative stresses of their habitat. Many halophytes have been used as a traditional food and medical supply, especially by African and Asian cultures. This scientific work evaluated the antibiotic, antioxidant, immunostimulant and metal chelating properties of Atriplex halimus L., Arthrocnemum macrostachyum Moric., Carpobrotus edulis L., Juncus acutus L. and Plantago coronopus L., from the Algarve coast. The antibiotic properties were tested against Listonella anguillarum, Photobacterium damselae piscicida and Vibrio fischeri. The immunostimulant properties were tested with cytochrome c and Griess assays on Sparus aurata head-kidney phagocytes. J. acutus ether extract inhibited the growth of P. damselae piscicida. A. macrostachyum, A. halimus, C. edulis, Juncus acutus and P. coronopus displayed antioxidant, copper chelating and iron chelating properties. These plants show potential as sources of bioactive compounds with application in aquaculture and in other fields.

The effect of stress on egg quality in farmed Atlantic Cod (Gadus morhua L.)

Dissertação de mestrado, Aquacultura, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2011