| Summary: | The growth potentials of Tetraselmis suecica (Kylin) Butch and Isochrysis galbana Parke in fish farm and aquarium effluents were assessed. Initially each algae was grown in one of six different isonitrogenous solutions, further enriched to supply phosphate, trace elements and vitamins. The cultures were continuously aerated, illuminated and maintained at l8°/l9°C. The growth obtained for T. suecica ranged from 212.2 X 10⁴ cells mlˉ¹ (urea 2) to 430.7 X 10⁴ cells mlˉ¹ (sodium nitrate 2), and for I. galbana from 105.9 X 10⁴ cells mlˉ¹ (urea 2) to 419.6 x 10⁴ cells mlˉ¹ (sodium nitrate 2). Fish farm and aquarium effluents were analysed with respect to inorganic nitrogen and phosphate, and the above experiment repeated replacing the defined media by selected effluents, enriched with vitamins only. Once again the cultures were continuously aerated, illuminated, and maintained at l8°/l9°C. The light was more uniform but less intense than in experiment one. The T. suecica growth varied from 91.9 x 10⁴ cells ml (sample l) to 312 x 10⁴ cells mlˉ¹ (sample 8), and for I. galbana from no growth (samples 1 and 3) to 304.2 x 10⁴ cells mlˉ¹ (sample 2). Finally a model recycling system was established incorporating the growth of T. suecica to enhance water quality by the removal of certain ions produced by the oyster, Crassostrea gigas Thunberg, and to provide food for the oysters. The algal culture vessel was continually enriched with shellfish effluent. The algal culture vessel, initially stocked at 500 x 10³ cells mlˉ¹ was depleted of cells in three days. Restocking at a higher cell density produced an equilibrium in the culture vessel, fluctuating between 70 and 90,000 cells m0lˉ¹, and although no oysters died during the experiment no attempts were made to determine their condition. The oysters spawned on the 23rd and 25th day of the experiment, probably initiated by a temperature rise to 20°C, turning the water, opaque, and necessitating a complete flush through and water change. The system was observed for a further week but no measurements were taken, other than visual observations.
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