The search for new biological sources of commercial value is a major goal for the sustainable management of natural resources. The huge amount of fishery by-catch or processing by-products continuously produced needs to be managed to avoid environmental problems and keep resource sustainability. Fishery by-products can represent an interesting source of high added value bioactive compounds, such as proteins, carbohydrates, collagen, polyunsaturated fatty acids, chitin, polyphenolic constituents, carotenoids, vitamins, alkaloids, tocopherols, tocotrienols, toxins; nevertheless, their biotechnological potential is still largely underutilized. Depending on their structural and functional characteristics, marine-derived biomolecules can find several applications in food industry, agriculture, biotechnological (chemical, industrial or environmental) fields. Fish internal organs are a rich and underexplored source of bioactive compounds; the fish gut microbiota biosynthesizes essential or short-chain fatty acids, vitamins, minerals or enzymes and is also a source of probiotic candidates, in turn producing bioactive compounds with antibiotic and biosurfactant/bioemulsifier activities. Chemical, enzymatic and/or microbial processing of fishery by-catch or processing by-products allows the production of different valuable bioactive compounds; to date, however, the lack of cost-effective extraction strategies so far has prevented their exploitation on a large scale. Standardization and optimization of extraction procedures are urgently required, as processing conditions can affect the qualitative and quantitative properties of these biomolecules. Valorization routes for such raw materials can provide a great additional value for companies involved in the field of bioprospecting. The present review aims at collecting current knowledge on fishery by-catch or by-products, exploring the valorization of their active biomolecules, in application of the circular economy paradigm applied to the fishery field. It will address specific issues from a biorefinery perspective: (i) fish tissues and organs as potential sources of metabolites, antibiotics and probiotics; (ii) screening for bioactive compounds; (iii) extraction processes and innovative technologies for purification and chemical characterization; (iv) energy production technologies for the exhausted biomass. We provide a general perspective on the techno-economic feasibility and the environmental footprint of the production process, as well as on the definition of legal constraints for the new products production and commercial use.

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Microbial communities play different functions in the digestive tract of fish and represent a source of bioactive compounds. This study was aimed to detect the presence of biosurfactant (BS)-producing bacteria in the intestine of gilthead sea bream (Sparus aurata L.) to select strains candidate for biotechnological applications in aquaculture. A total of 100 bacterial strains were isolated from the guts of three groups of fish and analysed by different qualitative screening tests and the tensiometric analysis. BSs were extracted, characterized by thin-layer chromatography (TLC) and their antibacterial activity against bacterial pathogens of interest in aquaculture was determined. A total of 17 out of 100 strains, affiliated to the genera Pseudomonas (11 isolates), Acinetobacter (1 isolate), Sphingomonas (4 isolates) andAeromonas (1 isolate), displayed a stable emulsion production with the E 24 index from 0% to 44%, a surface tension reduction from 8.3 to 30 mN/m and 11 of them exhibited antibacterial activity against fish pathogens. The TLC analysis indicated that the intestinal BSs consisted of compounds ascribed to the class of glycolipidsrhamnolipids. This is the first study reporting on the isolation and selection of BSproducing bacteria from fish gut, a natural novel source of surface active compounds with potential biotechnological applications in aquaculture.

The marine biosphere represents a yet underexploited natural source of bioactive compounds, mainly of microbial origin. Among them, biosurfactants (BSs) are functional molecules, which are attracting a great interest due to their biocompatibility, versatility, and applications in several biotechnological fields. BSs are surface active amphipathic compounds, containing both a hydrophilic and a hydrophobic moiety, which are grouped in low (glycolipids and lipopeptides) or high molecular weight (polymeric complexes) compounds. A number of environmental factors such as pH, salinity, temperature, and nutrient availability can affect microbial BS production. Marine microorganisms with different phylogenetic affiliations and isolated from several marine habitats (e.g., seawater, sediments, and higher organisms) worldwide (spanning from the Mediterranean Sea to Antarctica) have been reported as surfactant producers. However, most of the marine microbial world remains still unexplored. The present chapter aims at giving a general overview on the recent advances about BSs of marine origin, in order to enhance the knowledge inherent their production, chemical characterization and identification, interesting biological properties, and potential biotechnological applications.

SummaryForty five accessions of Sardinian germplasm of Medicago polymorpha L., derived from a wide range of climatic and edaphic conditions, were evaluated to identify useful genetic resources for the development of cultivars for rainfed Mediterranean conditions. The accessions were assessed for variation in morphological, agronomic and biochemical traits. Considerable variation was found between populations indicating the potential for selection.