In recent years, discharged nutrient from the fish culture farms has been causing the problem of self-pollution in the farming area, and we have been recommended integrated culture with various alga for fish farming. In order to execute integrated culture of Ulva ohnoi and red sea bream Pagrus major, we set conditions for culturing U. ohnoi in a farm of red sea bream in Tanabe Bay, Japan. Then, nitrogen (N) and phosphorus (P) budgets in the fish-alga integrated culture system were studied. The culture cage of U. ohnoi was placed in a block adjacent to a fish culture cage (3×3×3 m) to reduce the loads of nutrient discharge from the fish cage. From July to September 2003, 260 young fish (mean weight of 38.4 ± 5.4 g) of red sea bream were cultured in the cage by feeding 26.8 kg of artificial compound feed (EP-pellet) containing 1,951 g of nitrogen and 281 g of phosphorus. At the end, 19.8 kg of fish growth was obtained and 565 g (29.0 % of the given feed) of N and 164 g (58.4 %) of P were stored in the fish bodies. U. ohnoi absorbed N and P at estimated rates of 3.18-10.56 μmol wet-g^-1 hr^-1 and 0.09-0.31 μmol wet-g^-1 hr^-1, respectively, and  the  daily growth rate of U. ohnoi was  11.0-24.2 %, which varied with the initial input weight of thalli. At the most effective design, the total amounts of N and P absorbed by U. ohnoi corresponded to 7.0 % and 3.2 % of those in given food, respectively.

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It is reported that long-day conditions induce receptacle formation of Sargassum horneri grown in a laboratory-culture system. In this study, we examined inductive effects of experimental day length on wild thalli of a field population in receptacle formation. Materials (apical 5 cm segments of plants) were sampled in a population with reproductive season in spring, and every month from October to January when the population was in the rapid vegetative growth stage. The segments were cultured under 4 photoperiod regimes (8:16h, 10:14h, 12:12h and 14:10h L:D), 100 μmol photons m^-2 s^-1, 18-20 °C for 4 weeks and observed whether receptacles were formed or not.
October material was young and did not form receptacles under all photoperiod regimes during the experiment. However, November material formed receptacles under longer-day conditions, that was 100 % and 50 % in frequency under 14:10h and 12:12h L:D, respectively. Receptacle formation of December material was also promoted in longer day length, and no segments became reproductive under 8:16h L:D. January material formed receptacles under all photoperiod regimes, which indicated that plants in January had been already triggered for reproduction in the field. Though factor (s) triggering re-production of S. horneri in the field is still unclear, artificial long-day conditions are effective to induce receptacle formation on wild thalli in the vegetative growth stage.

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