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.
The objective of the study was to investigate the effect of high temperature on sex ratios of early stage rainbow trout (Onchorhynchus mykiss) in commercially farmed populations from distinct hatcheries. Almost 32500 larvae from five different farms were used in experiments as thermal groups and their corresponding controls. Temperature treatments were conducted at 17.5°C for 40 days starting at day 10 after hatching. In only one population, the sex ratio was skewed significantly in favor of females in thermally treated group (67.5%), when compared to control group (52.1%) and there was deviation from the expected 1:1 ratio. In the treatment group the females grew 8.3% more than males. However there was no repeatiblity and any skewness in sex ratio of progenies from photoperiod induced spawning. Survival rates were not affected by the thermal treatments. The results showed that the increasing of femaleness of farmed stocks is possible by thermal treatment in rainbow trout and which depends on percentage of thermosensitive individuals rather than genetic background of population.
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