Abstract. The purpose of the study was to obtain preliminary data on the effect of dietary protein on the growth of the thick-lipped grey mullet (Chelon labrosus) juveniles reared in net sea-cages. The juveniles (6.2 ± 0.61 g) were obtained from the wild and were stocked into net sea-cages at a stocking rate of 100 juveniles per cubic meter and fed with experimental diets including 25, 30, or 35% crude protein for 87 days. The highest mean weight and specific growth rate (SGR) were 39.5 g and 2.13% day -1 , respectively, at protein levels of 30%. The diet also resulted in the most efficient feed conversion ratio of 1.61.

Ethyl acetate extracts from 70 strains of marine-derived fungi, isolated from sponges, were screened against four fish pathogenic bacteria. Sixteen of the fungal isolates exhibited antibacterial activity against at least one pathogen. All the strains showed antibacterial activity against Vagococcus salmoninarum. Three isolates showed strong inhibition against all test pathogens and they may therefore be remarkable as a broadspectrum antimicrobial. Nine isolates showed antibacterial activity against Lactococcus garvieae, six were against Vibrio anguillarum, and four isolates inhibited the growth of Yersinia ruckeri. Co-culture of the fungus with the mix of the pathogen bacteria led to the induction of bioactivity in two isolates. Aspergillus iizukae produced strong and broadspectrum antibacterial activity against pathogens with minimum inhibitory concentrations of 0.8-406 mg mL À1 . The screening results confirmed the sponge associated fungi as a source of environmentally friendly antimicrobials that may contribute the sustainable development of aquaculture. In addition, co-culture technique is a promising strategy to increase antimicrobial activity that can stimulate the production of novel compounds, and increases the antimicrobial activities of marine derived fungi.

Fast, cheap and simple HPLC methods have been gaining importance in the field of antibiotic residue analysis especially in the context of environmentally friendly and sustainable aquaculture. An effective column-switching technique for HPLC using online extraction column was developed to eliminate the time consuming pretreatment procedures and to facilitate the high throughput analysis of sulfadiazine in fish plasma and muscle as well as in water samples. The standard curves for the determination of sulfadiazine residues from biological matrices and water have good linearity (r 2 > 0.996). The average recovery ranged from 92.2 to 118% with the relative standard deviations of 0.3-9.3%. Limits of detection were determined as 5.7 mg L À1 for water, 8.1 mg L À1 for plasma and 9.6 mg kg À1 for muscle, while limits of quantification were 18.9 mg L À1 for water, 26.9 mg L À1 for plasma and 31.9 mg kg À1 for muscle, respectively. Intra-and inter-day precisions were 0.3-9.3 and 0.4-6.7%, respectively. With the retention time of 12 min and total analysis time less than half an hour, this method provides an effective online extraction process and good sensitivity in liquid chromatography, and can be applied for the determination of residual sulfadiazine in water, fish plasma and muscle at lower than maximum residue level of 100 mg kg À1 fish.

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