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AbstractSeaweeds are considered novel feed ingredients, nutraceutical compounds and source of pigments and proteins. They appear to possess bioactive properties, such as hypolipidemic, antioxidant and immune-stimulative actions; furthermore, their proteins are considered just as nutritious as terrestrial vegetables. In the present work, rainbow trout (Oncorhynchus mykissWalbaum) was fed for 95 days with three diets: a fishmeal-based positive control diet (C+), a vegetable protein-based negative control diet (C−) and a diet similar to C − where 5% of soybean concentrate was replaced by a commercial blend of seaweeds (T). The monitored parameters were fish performance, physical and marketable characteristics, fillet oxidative status and fatty acid content. The estimated indices of enzyme activities involved in lipid metabolism were calculated. Fish performances were reduced in C − and T fish; C − and T fillet fatty acid (FA) profiles globally showed the same pattern and were distinct from C+, i.e. with a lower content of polyunsaturated FAs and a higher content of monounsaturated and polyunsaturated n6 FAs; contrarywise, saturated FAs were significantly lower in T group in comparison to the other two groups (p < .01). The estimated indices of enzyme activity highlighted differences between dietary groups; desaturase activities of C18 and n3 FAs were higher in T in comparison to C− (p < .001). A slight impoverishment of antioxidant activity was found in T compared to C + group. Dietary seaweeds seemed to be capable of influencing fillet FA composition as well as the activity of enzymes related to lipid metabolism. Further studies in this regard are encouraged.HighlightsSeaweeds are novel feed ingredients with nutraceutical propertiesSaturated fatty acids of rainbow trout fillets were lowered by seaweed inclusion in the dietEstimated desaturase activities of C18 and n3 fatty acids were higher in seaweed-fed trout

The applicability of a novel procedure for the disinfection of microbiologically polluted waters from fish-farming ponds, based on the combined action of visible light including sunlight and porphyrin-type photosensitising agents, has been investigated using a cell cultures of a Gram-positive bacterium meticillin-resistant Staphylococcus aureus, a Gram-negative bacterium Escherichia coli and a fungal pathogen Saprolegniaspp.; b pilot aquaculture plants involving either spontaneously or artificially Saprolegnia-infected rainbow trout Oncorhynchus mykiss. The results obtained by using two cationic porphyrins, namely a tetra-substituted N-methyl-pyridyl-porphine C1 and its analogue where one N-methyl group had been replaced by a N-tetradecyl chain C14, and low intensity visible light irradiation showed an extensive up to 6–7 log decrease in the bacterialfungal population after short incubation and irradiation times in the presence of micromolar photosensitiser concentrations. Moreover, C14 showed some toxic effect also in the absence of light. Extension of these studies to the pilot plants indicated that both C1 light and C14 can prevent Saprolegniainfections or promote the cure of saprolegniasis in infected trout by treatments with submicromolar porphyrin doses. The procedure appears to be of low cost and to have a low environmental impact.